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PeytonPlayz595/Shadow-4.0 | main | # Shadow-4.0
# Running the Desktop Runtime
**Note: Requires a physical display to run, will NOT run on codespaces, ANY online terminal without a graphical display, or ANY ssh without X11 forwarding (Pretty much self explanitory but for the people who didn't know)**
**^^^**
**If you STILL don't understand, it basically means you have to run it on YOUR personal computer. You most likely will not be able to use it in a browser VM without a graphical interface or over SSH**
1. Clone this GitHub repo (Either using git or manual download)
2. cd into the directory of this repo
3. Run `gradlew runclient` and wait for it to finish compiling
| Optifine client for Eaglercraft u27 with support for EaglerForge mods | eaglercraft,eaglercraftx,javascript,minecraft,optifine,webgl,eaglerforge | 2024-04-11T10:35:47Z | 2024-04-21T16:06:36Z | null | 4 | 10 | 29 | 0 | 15 | 8 | null | null | HTML |
Shanisoni/the-deep-green-Web-Technologies | main | # Adventures-web
## Introduction
Adventures-web is a web project developed using HTML, CSS, and JavaScript. This project aims to [briefly describe the purpose or goal of your project].
## HTML Properties
- **color**: Sets the color of text.
- **font-family**: Specifies the font(s) to be used for text.
- **font-size**: Sets the size of text.
- **font-weight**: Specifies the weight (boldness) of text.
### Semantic Elements
- `<header>`: Represents introductory content at the beginning of a document or section.
- `<footer>`: Represents the footer of a document or section.
- `<article>`: Represents self-contained content that could exist independently.
- `<section>`: Represents a thematic grouping of content.
- `<aside>`: Represents content tangentially related to the content around it.
- `<main>`: Represents the main content of the document.
- `<figure>`: Represents self-contained content, such as images or diagrams, with optional captions.
- `<figcaption>`: Represents the caption for a `<figure>` element.
### Interactive Elements
- `<button>`: Defines a clickable button.
- `<details>`: Represents additional information or controls that the user can view or hide.
- `<summary>`: Represents a summary, caption, or legend for a `<details>` element.
- `<input>`: Provides various types of input controls (text fields, checkboxes, radio buttons, etc.).
- `<label>`: Associates a label with a form control.
- `<select>`: Creates a dropdown list.
- `<datalist>`: Defines a list of pre-defined options for an `<input>` element.
- `<progress>`: Represents the progress of a task.
- `<meter>`: Represents a scalar measurement within a known range.
### Embedded Content
- `<iframe>`: Embeds a separate HTML page into the current document.
- `<canvas>`: Provides a space for graphics rendering with JavaScript.
- `<svg>`: Defines scalable vector graphics.
- `<math>`: Represents complex mathematical expressions.
### Meta Information
- `<base>`: Specifies a base URL for all relative URLs in a document.
- `<link>`: Defines relationships between the current document and external resources.
- `<style>`: Contains style information for a document.
- `<script>`: Embeds or links to client-side scripts.
### Global Attributes
- **id**: Uniquely identifies an element within a document.
- **class**: Specifies one or more class names for an element, allowing CSS styling.
- **style**: Defines inline CSS styles for an element.
- **title**: Provides advisory information about an element.
### Event Attributes
- **onclick, onmouseover, onkeydown, etc.**: Assigns JavaScript event handlers to elements to respond to user actions.
### Document Structure
- `<html>`: The root element.
- `<head>`: Contains metadata about the document.
- `<title>`: Sets the title of the document.
- `<body>`: Contains the visible content of the document.
### Text Formatting
- `<h1>` to `<h6>`: Headings of different levels.
- `<p>`: Paragraph.
- `<strong>`: Bold text.
- `<em>`: Italicized text.
- `<u>`: Underlined text.
- `<blockquote>`: Block quote.
### Links and Navigation
- `<a>`: Anchor (hyperlink).
- **href**: Specifies the URL of the linked page.
- **target**: Specifies where to open the linked document.
- `<nav>`: Navigation links.
### Lists
- `<ul>`: Unordered list.
- `<ol>`: Ordered list.
- `<li>`: List item.
### Images
- `<img>`: Image.
- **src**: Specifies the URL of the image.
- **alt**: Specifies an alternate text for the image.
### Tables
- `<table>`: Defines a table.
- `<tr>`: Defines a row in a table.
- `<td>`: Defines a cell in a table.
- `<th>`: Defines a header cell in a table.
### Forms
- `<form>`: Defines a form.
- `<input>`: Input control.
- **type**: Specifies the type of input control (text, checkbox, radio, etc.).
- `<textarea>`: Multi-line text input control.
- `<select>`: Dropdown list.
- `<option>`: Defines an option in a dropdown list.
- `<button>`: Defines a clickable button.
### Media
- `<audio>`: Audio content.
- `<video>`: Video content.
- `<source>`: Defines multiple media resources for media elements.
### Metadata
- `<meta>`: Metadata about the HTML document.
- **charset**: Specifies the character encoding for the document.
- **content**: Specifies the value of the meta tag.
### Style and Scripting
- `<style>`: Defines style information for a document.
- `<script>`: Defines a client-side script.
- **src**: Specifies the URL of an external script file.
## CSS Properties
- **font-style**: Sets the style (italic, oblique, normal) of text.
- **text-align**: Sets the horizontal alignment of text.
- **text-decoration**: Specifies decorations added to text (underline, overline, line-through).
- **background-color**: Sets the background color of an element.
- **background-image**: Specifies an image to be used as the background.
- **border**: Sets the border properties of an element.
- **padding**: Specifies the padding inside an element's border.
- **margin**: Sets the margin outside an element's border.
- **width**: Sets the width of an element.
- **height**: Sets the height of an element.
- **display**: Specifies how an element is displayed.
- **position**: Specifies the positioning method of an element.
- **float**: Specifies whether an element should float to the left, right, or none.
- **z-index**: Sets the stack order of positioned elements.
- **opacity**: Sets the opacity level for an element.
- **box-shadow**: Adds shadow effects to an element's box.
- **text-shadow**: Adds shadow effects to text.
- **transition**: Specifies the transition effects on an element.
- **animation**: Defines animations on an element.
- **overflow**: Specifies what happens if content overflows an element's box.
- **cursor**: Specifies the type of cursor to be displayed when pointing over an element.
- **list-style**: Sets the style of list items (bullet points, numbering).
- **outline**: Sets the outline properties for an element.
## JavaScript Features
- **DOM Manipulation**: JavaScript allows you to manipulate the Document Object Model (DOM) dynamically, enabling interactions with HTML and CSS.
- **Event Handling**: JavaScript provides the ability to respond to user actions such as clicks, mouse movements, and keyboard input through event handling.
- **Asynchronous Programming**: JavaScript supports asynchronous programming, allowing you to perform tasks such as fetching data from servers without blocking the main thread.
- **ES6 Features**: JavaScript ES6 introduces new features such as arrow functions, template literals, and destructuring assignment, enhancing code readability and maintainability.
## Usage
[Provide instructions on how to use your project or how to set it up for development]
## Contributions
[Specify guidelines for contributions or how others can contribute to your project]
## License
[Choose and specify the
### Meta Information
- `<base>`: Specifies a base URL for all relative URLs in a document.
- `<link>`: Defines relationships between the current document and external resources.
- `<style>`: Contains style information for a document.
- `<script>`: Embeds or links to client-side scripts.
### Global Attributes
- **id**: Uniquely identifies an element within a document.
- **class**: Specifies one or more class names for an element, allowing CSS styling.
- **style**: Defines inline CSS styles for an element.
- **title**: Provides advisory information about an element.
### Event Attributes
- **onclick, onmouseover, onkeydown, etc.**: Assigns JavaScript event handlers to elements to respond to user actions.
### Document Structure
- `<html>`: The root element.
- `<head>`: Contains metadata about the document.
- `<title>`: Sets the title of the document.
- `<body>`: Contains the visible content of the document.
### Text Formatting
- `<h1>` to `<h6>`: Headings of different levels.
- `<p>`: Paragraph.
- `<strong>`: Bold text.
- `<em>`: Italicized text.
- `<u>`: Underlined text.
- `<blockquote>`: Block quote.
### Links and Navigation
- `<a>`: Anchor (hyperlink).
- **href**: Specifies the URL of the linked page.
- **target**: Specifies where to open the linked document.
- `<nav>`: Navigation links.
### Lists
- `<ul>`: Unordered list.
- `<ol>`: Ordered list.
- `<li>`: List item.
### Images
- `<img>`: Image.
- **src**: Specifies the URL of the image.
- **alt**: Specifies an alternate text for the image.
### Tables
- `<table>`: Defines a table.
- `<tr>`: Defines a row in a table.
- `<td>`: Defines a cell in a table.
- `<th>`: Defines a header cell in a table.
### Forms
- `<form>`: Defines a form.
- `<input>`: Input control.
- **type**: Specifies the type of input control (text, checkbox, radio, etc.).
- `<textarea>`: Multi-line text input control.
- `<select>`: Dropdown list.
- `<option>`: Defines an option in a dropdown list.
- `<button>`: Defines a clickable button.
### Media
- `<audio>`: Audio content.
- `<video>`: Video content.
- `<source>`: Defines multiple media resources for media elements.
### Metadata
- `<meta>`: Metadata about the HTML document.
- **charset**: Specifies the character encoding for the document.
- **content**: Specifies the value of the meta tag.
### Style and Scripting
- `<style>`: Defines style information for a document.
- `<script>`: Defines a client-side script.
- **src**: Specifies the URL of an external script file.
## CSS Properties
- **font-style**: Sets the style (italic, oblique, normal) of text.
- **text-align**: Sets the horizontal alignment of text.
- **text-decoration**: Specifies decorations added to text (underline, overline, line-through).
- **background-color**: Sets the background color of an element.
- **background-image**: Specifies an image to be used as the background.
- **border**: Sets the border properties of an element.
- **padding**: Specifies the padding inside an element's border.
- **margin**: Sets the margin outside an element's border.
- **width**: Sets the width of an element.
- **height**: Sets the height of an element.
- **display**: Specifies how an element is displayed.
- **position**: Specifies the positioning method of an element.
- **float**: Specifies whether an element should float to the left, right, or none.
- **z-index**: Sets the stack order of positioned elements.
- **opacity**: Sets the opacity level for an element.
- **box-shadow**: Adds shadow effects to an element's box.
- **text-shadow**: Adds shadow effects to text.
- **transition**: Specifies the transition effects on an element.
- **animation**: Defines animations on an element.
- **overflow**: Specifies what happens if content overflows an element's box.
- **cursor**: Specifies the type of cursor to be displayed when pointing over an element.
- **list-style**: Sets the style of list items (bullet points, numbering).
- **outline**: Sets the outline properties for an element.
## Usage
To use the Adventures-web project, follow these steps:
1. Clone the repository to your local machine using Git:
2. Open the project directory:
3. 3. Open the index.html file in your preferred web browser.
4. Explore the project and interact with its features.
## Contributions
Contributions to Adventures-web are welcome and encouraged! To contribute to the project, please follow these guidelines:
1. Fork the repository on GitHub.
2. Make your desired changes to the codebase.
3. Ensure that your changes adhere to the project's coding conventions and style guidelines.
4. Test your changes thoroughly to ensure they work as expected.
5. Submit a pull request with a clear description of your changes and the problem they solve.
6. Your pull request will be reviewed by the project maintainers, and any necessary feedback will be provided.
7. Once your pull request is approved, it will be merged into the main branch.
## License
This project is licensed under the [MIT License](https://opensource.org/licenses/MIT). You are free to use, modify, and distribute the code for personal or commercial purposes. See the [LICENSE](LICENSE) file for more details.
| "Embark on a journey of cutting-edge web development as I craft a dynamic and visually captivating web application. Harnessing the latest in CSS wizardry, HTML semantics, and JavaScript mastery, My project aims to redefine the digital experience. Dive into a world of seamless animations, fluid layouts, and interactive interfaces that engage users | css3,html5,javascript,css,css-animations,css-animations-2023,css-flexbox,css-flexbox-grid,css-flexbox-grid-layout,css-framework | 2024-03-15T17:05:11Z | 2024-05-22T03:29:32Z | null | 1 | 0 | 24 | 0 | 0 | 8 | null | MIT | HTML |
tenoxui/css | main | <p align="center">
<a href="https://tenoxui.web.app/">
<img src="https://tenoxui.web.app/img/tenoxui.svg" alt="TenoxUI Logo" width='300' height='300'
>
</a>
</p>
<h1 align="center">TenoxUI v0.10</h1>
<p align="center">
A CSS Framework without css file :D
<br>
<a href="https://tenoxui.web.app/docs/start">Full Documentation</a>
</p>
<h2>Installation</h2>
Using npm:
```bash
npm i tenoxui --save-dev
```
Using CDN :
```html
<script src="https://cdn.jsdelivr.net/npm/tenoxui@latest/dist/js/tenoxui.min.js"></script>
```
<h2>Setup Project</h2>
Here is simple usage of tenoxui on your project.
### HTML :
```html
<!doctype html>
<html>
<head>
<title>Tester</title>
<script src="https://cdn.jsdelivr.net/npm/tenoxui"></script>
</head>
<body>
<h1 class="text-#ccf654 fs-4rem">Hello World!</h1>
<script>
tenoxui({ text: "color", fs: "fontSize" });
</script>
</body>
</html>
```
### React :
First, you need to add tenoxui to your project :
```sh
npm i tenoxui --save-dev
```
Then, on your app.jsx file :
```jsx
import { useLayoutEffect } from "react";
import tenoxui from "tenoxui";
const App = () => {
useLayoutEffect(() => {
// add tenoxui
tenoxui({ text: "color", fs: "fontSize" });
}, []);
return <h1 className="text-#ccf654 fs-4rem">Hello World!</h1>;
};
export default App;
```
<h2>Types and Properties</h2>
TenoxUI also provide a library of defined types and properties that you can use without defining it one by one. You can add the `property` to your project using CDN or install it using npm :
```html
<script src="https://cdn.jsdelivr.net/npm/@tenoxui/property"></script>
```
Or :
```sh
npm i tenoxui @tenoxui/property
```
```jsx
import tenoxui from "tenoxui";
import property from "@tenoxui/property";
```
To use the `property` you can simply attach it inside tenoxui function as its parameter. Like this :
```html
<script>
tenoxui(property);
</script>
```
Or ReactJS :
```jsx
import { useLayoutEffect } from "react";
import tenoxui from "tenoxui";
import property from "@tenoxui/property";
const App = () => {
useLayoutEffect(() => {
// add tenoxui
tenoxui(property); // use tenoxui property
}, []);
return <h1 className="tc-red">Hello World!</h1>;
};
export default App;
```
You can see all types and properties on [GitHub Repository](https://github.com/tenoxui/property) or [Here](https://tenoxui.github.io/property)
<h4>More</h4>
- [tenoxui/css](https://github.com/tenoxui/css)
- [tenoxui/website](https://github.com/tenoxui/website)
- [tenoxui/property](https://github.com/tenoxui/property)
- [tenoxui/react](https://github.com/tenoxui/react)
- [tenoxui/styles](https://github.com/tenoxui/styles)
- [tenoxui/cli](https://github.com/tenoxui/cli)
- [tenoxui/components](https://github.com/tenoxui/components)
| A CSS Framework without any CSS file :D | css,css-framework,javascript,css-in-js,css3,frontend-tools,html,js,lightweight-framework,react | 2024-03-31T04:19:52Z | 2024-05-22T12:36:13Z | 2024-05-20T10:55:18Z | 2 | 23 | 274 | 0 | 2 | 8 | null | MIT | TypeScript |
YevheniiaSimaka/Specify | main | # Specify
<img width="100%" alt="Home View" src="https://github.com/YevheniiaSimaka/Specify_SummitHacks/assets/112284703/24c32245-e824-4be9-b298-37cb074c65c6">
<img width="50%" alt="Tasks View" src="https://github.com/YevheniiaSimaka/Specify_SummitHacks/assets/112284703/b310904c-4770-4a28-a927-5db46d5c39ae"><img width="50%" alt="Pomodoro" src="https://github.com/YevheniiaSimaka/Specify_SummitHacks/assets/112284703/4b60b588-1d6e-47b3-90d0-b7a662790c76">
I often have so many tasks that I just write down on sticky notes and eventually forget about them, and I've decide to switch it up and actually get organized in my life. I figured that the way I was organizing my tasks before was sticky notes with different colors representing different categories, so I decided to implement something similar digitally.
## Technologies used
[](https://skillicons.dev)
## Demo
[Specidy - Live Demo](https://specify-summit-hacks.vercel.app)
## Functionality
- Authentication with password encryption
- Create Tasks
- Edit Tasks
- Delete Tasks
- Sort Tasks
- Search Tasks
- Grid/List View
- Pomodoro Timer
- Add simple todos
- Delete simple todos
## Run Locally
Clone the project
```bash
git clone https://github.com/YevheniiaSimaka/Specify_SummitHacks
```
Go to the project directory
```bash
cd my-project
```
Install dependencies
```bash
npm i
```
Add .env
```bash
DATABASE_URL=
NEXTAUTH_SECRET=
```
Start the server
```bash
npm run dev
```
| Get things done with Specify! | javascript,mongodb,nextjs,prisma,tailwind,typescript | 2024-04-27T23:53:46Z | 2024-05-12T01:08:09Z | null | 1 | 0 | 32 | 0 | 1 | 8 | null | MIT | JavaScript |
happy358/TornPaper | main | # TornPaper
Creating torn edge and grunge paper effect using SVG and JavaScript.
## Demo
* TornPaper.js demo
[https://codepen.io/wakana-k/full/PogRqLx](https://codepen.io/wakana-k/full/PogRqLx)
* clip-path animation demo
[https://codepen.io/wakana-k/full/RwOMdoY](https://codepen.io/wakana-k/full/RwOMdoY)
* Torn paper photo gallery
[https://codepen.io/wakana-k/full/ExJEvor](https://codepen.io/wakana-k/full/ExJEvor)
## Usage
### html:
```html
<script src="https://cdn.jsdelivr.net/gh/happy358/TornPaper@v0.0.3/tornpaper.min.js"></script>
<script>
new Tornpaper();
</script>
```
### css:
```css
.your-class {
filter: url(#filter_tornpaper);
}
```
#### e.g. With background-color
```css
.your-class {
filter: url(#filter_tornpaper);
background-color: pink;
}
```
#### e.g. With background-image
```css
.your-class {
filter: url(#filter_tornpaper);
background: url("https://source.unsplash.com/random/") center/cover;
}
```
## Options
```js
new Tornpaper({
filterName : "filter_tornpaper", // cunstom filter-id, default:"filter_tornpaper"
seed : 1, // random seed, default:random number
tornFrequency : 0.05, // 0=no torn edge, default:0.05
tornScale : 10,
grungeFrequency : 0.03, // 0=no grunge texture, default:0.03
grungeScale : 3
});
```
## References
- Inspired by fguilleme.
[https://codepen.io/fguilleme/pen/MMyKXB](https://codepen.io/fguilleme/pen/MMyKXB)
- SVG Filter Effects: Creating Texture with <feTurbulence>
[https://tympanus.net/codrops/2019/02/19/svg-filter-effects-creating-texture-with-feturbulence/](https://tympanus.net/codrops/2019/02/19/svg-filter-effects-creating-texture-with-feturbulence/)
Thanks!
| null | grunge,torn,grungepaper,tornpaper,javascript,js,paper,svg | 2024-04-07T14:58:07Z | 2024-04-10T21:59:26Z | 2024-04-10T21:59:26Z | 1 | 0 | 80 | 0 | 0 | 8 | null | MIT | JavaScript |
danieleverest/interview-questions-javascript | main | # JavaScript Interview Questions & Answers
> Click :star:if you like the project and follow [@danieleverest](https://www.facebook.com/profile.php?id=61556352754672) for more updates. Coding questions available [here](#coding-exercise). PDF and Epub versions available at [actions tab](https://github.com/danieleverest/JavaScript-Interview-Questions/actions).
---
<p align="center">
<a href=https://zerotomastery.io/?utm_source=github&utm_medium=sponsor&utm_campaign=javascript-interview-questions>
<img src=https://process.fs.teachablecdn.com/ADNupMnWyR7kCWRvm76Laz/resize=height:70/https://www.filepicker.io/api/file/AKYtjj5SSGyJuyZrkAB2 alt="ZTM Logo" width="100" height="50">
</a>
<p align="center">
<ol>
<li>Take this <a href=https://links.zerotomastery.io/jsp_sudheer>JavaScript Projects</a> course to go from a JS beginner to confidently building your own projects</li>
<li>Take this <a href=https://links.zerotomastery.io/mci_sudheer2>coding interview bootcamp</a> if you’re serious about getting hired and don’t have a CS degree</li>
<li>Take this <a href=https://links.zerotomastery.io/ajs_sudheer>Advanced JavaScript Course</a> to learn advanced JS concepts and become a top JS developer</li>
</ol>
</p>
</p>
---
**Note:** Please check [DataStructures and Algorithms](https://github.com/danieleverest/datastructures-algorithms) for DSA related questions or problems.
### Table of Contents
| No. | Questions |
| --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 1 | [What are the possible ways to create objects in JavaScript](#what-are-the-possible-ways-to-create-objects-in-javascript) |
| 2 | [What is a prototype chain](#what-is-a-prototype-chain) |
| 3 | [What is the difference between Call, Apply and Bind](#what-is-the-difference-between-call-apply-and-bind) |
| 4 | [What is JSON and its common operations](#what-is-json-and-its-common-operations) |
| 5 | [What is the purpose of the array slice method](#what-is-the-purpose-of-the-array-slice-method) |
| 6 | [What is the purpose of the array splice method](#what-is-the-purpose-of-the-array-splice-method) |
| 7 | [What is the difference between slice and splice](#what-is-the-difference-between-slice-and-splice) |
| 8 | [How do you compare an Object with a Map](#how-do-you-compare-object-and-map) |
| 9 | [What is the difference between == and === operators](#what-is-the-difference-between--and--operators) |
| 10 | [What are lambda expression or arrow functions](#what-are-lambda-or-arrow-functions) |
| 11 | [What is a first class function](#what-is-a-first-class-function) |
| 12 | [What is a first order function](#what-is-a-first-order-function) |
| 13 | [What is a higher order function](#what-is-a-higher-order-function) |
| 14 | [What is a unary function](#what-is-a-unary-function) |
| 15 | [What is the currying function](#what-is-the-currying-function) |
| 16 | [What is a pure function](#what-is-a-pure-function) |
| 17 | [What is the purpose of the let keyword](#what-is-the-purpose-of-the-let-keyword) |
| 18 | [What is the difference between let and var](#what-is-the-difference-between-let-and-var) |
| 19 | [What is the reason to choose the name let as a keyword](#what-is-the-reason-to-choose-the-name-let-as-a-keyword) |
| 20 | [How do you redeclare variables in switch block without an error](#how-do-you-redeclare-variables-in-switch-block-without-an-error) |
| 21 | [What is the Temporal Dead Zone](#what-is-the-temporal-dead-zone) |
| 22 | [What is IIFE(Immediately Invoked Function Expression)](#what-is-iifeimmediately-invoked-function-expression) |
| 23 | [How do you decode or encode a URL in JavaScript?](#how-do-you-decode-or-encode-a-url-in-javascript) |
| 24 | [What is memoization](#what-is-memoization) |
| 25 | [What is Hoisting](#what-is-hoisting) |
| 26 | [What are classes in ES6](#what-are-classes-in-es6) |
| 27 | [What are closures](#what-are-closures) |
| 28 | [What are modules](#what-are-modules) |
| 29 | [Why do you need modules](#why-do-you-need-modules) |
| 30 | [What is scope in javascript](#what-is-scope-in-javascript) |
| 31 | [What is a service worker](#what-is-a-service-worker) |
| 32 | [How do you manipulate DOM using a service worker](#how-do-you-manipulate-dom-using-a-service-worker) |
| 33 | [How do you reuse information across service worker restarts](#how-do-you-reuse-information-across-service-worker-restarts) |
| 34 | [What is IndexedDB](#what-is-indexeddb) |
| 35 | [What is web storage](#what-is-web-storage) |
| 36 | [What is a post message](#what-is-a-post-message) |
| 37 | [What is a cookie](#what-is-a-cookie) |
| 38 | [Why do you need a Cookie](#why-do-you-need-a-cookie) |
| 39 | [What are the options in a cookie](#what-are-the-options-in-a-cookie) |
| 40 | [How do you delete a cookie](#how-do-you-delete-a-cookie) |
| 41 | [What are the differences between cookie, local storage and session storage](#What-are-the-differences-between-cookie-local-storage-and-session-storage) |
| 42 | [What is the main difference between localStorage and sessionStorage](#what-is-the-main-difference-between-localstorage-and-sessionstorage) |
| 43 | [How do you access web storage](#how-do-you-access-web-storage) |
| 44 | [What are the methods available on session storage](#what-are-the-methods-available-on-session-storage) |
| 45 | [What is a storage event and its event handler](#what-is-a-storage-event-and-its-event-handler) |
| 46 | [Why do you need web storage](#why-do-you-need-web-storage) |
| 47 | [How do you check web storage browser support](#how-do-you-check-web-storage-browser-support) |
| 48 | [How do you check web workers browser support](#how-do-you-check-web-workers-browser-support) |
| 49 | [Give an example of a web worker](#give-an-example-of-a-web-worker) |
| 50 | [What are the restrictions of web workers on DOM](#what-are-the-restrictions-of-web-workers-on-dom) |
| 51 | [What is a promise](#what-is-a-promise) |
| 52 | [Why do you need a promise](#why-do-you-need-a-promise) |
| 53 | [What are the three states of promise](#what-are-the-three-states-of-promise) |
| 54 | [What is a callback function](#what-is-a-callback-function) |
| 55 | [Why do we need callbacks](#why-do-we-need-callbacks) |
| 56 | [What is a callback hell](#what-is-a-callback-hell) |
| 57 | [What are server-sent events](#what-are-server-sent-events) |
| 58 | [How do you receive server-sent event notifications](#how-do-you-receive-server-sent-event-notifications) |
| 59 | [How do you check browser support for server-sent events](#how-do-you-check-browser-support-for-server-sent-events) |
| 60 | [What are the events available for server sent events](#what-are-the-events-available-for-server-sent-events) |
| 61 | [What are the main rules of promise](#what-are-the-main-rules-of-promise) |
| 62 | [What is callback in callback](#what-is-callback-in-callback) |
| 63 | [What is promise chaining](#what-is-promise-chaining) |
| 64 | [What is promise.all](#what-is-promiseall) |
| 65 | [What is the purpose of the race method in promise](#what-is-the-purpose-of-the-race-method-in-promise) |
| 66 | [What is a strict mode in javascript](#what-is-a-strict-mode-in-javascript) |
| 67 | [Why do you need strict mode](#why-do-you-need-strict-mode) |
| 68 | [How do you declare strict mode](#how-do-you-declare-strict-mode) |
| 69 | [What is the purpose of double exclamation](#what-is-the-purpose-of-double-exclamation) |
| 70 | [What is the purpose of the delete operator](#what-is-the-purpose-of-the-delete-operator) |
| 71 | [What is typeof operator](#what-is-typeof-operator) |
| 72 | [What is undefined property](#what-is-undefined-property) |
| 73 | [What is null value](#what-is-null-value) |
| 74 | [What is the difference between null and undefined](#what-is-the-difference-between-null-and-undefined) |
| 75 | [What is eval](#What-is-eval) |
| 76 | [What is the difference between window and document](#what-is-the-difference-between-window-and-document) |
| 77 | [How do you access history in javascript](#how-do-you-access-history-in-javascript) |
| 78 | [How do you detect caps lock key turned on or not](#how-do-you-detect-caps-lock-key-turned-on-or-not) |
| 79 | [What is isNaN](#what-is-isnan) |
| 80 | [What are the differences between undeclared and undefined variables](#what-are-the-differences-between-undeclared-and-undefined-variables) |
| 81 | [What are global variables](#what-are-global-variables) |
| 82 | [What are the problems with global variables](#what-are-the-problems-with-global-variables) |
| 83 | [What is NaN property](#what-is-nan-property) |
| 84 | [What is the purpose of isFinite function](#what-is-the-purpose-of-isfinite-function) |
| 85 | [What is an event flow](#what-is-an-event-flow) |
| 86 | [What is event bubbling](#what-is-event-bubbling) |
| 87 | [What is event capturing](#what-is-event-capturing) |
| 88 | [How do you submit a form using JavaScript](#how-do-you-submit-a-form-using-javascript) |
| 89 | [How do you find operating system details](#how-do-you-find-operating-system-details) |
| 90 | [What is the difference between document load and DOMContentLoaded events](#what-is-the-difference-between-document-load-and-domcontentloaded-events) |
| 91 | [What is the difference between native, host and user objects](#what-is-the-difference-between-native-host-and-user-objects) |
| 92 | [What are the tools or techniques used for debugging JavaScript code](#what-are-the-tools-or-techniques-used-for-debugging-javascript-code) |
| 93 | [What are the pros and cons of promises over callbacks](#what-are-the-pros-and-cons-of-promises-over-callbacks) |
| 94 | [What is the difference between an attribute and a property](#what-is-the-difference-between-an-attribute-and-a-property) |
| 95 | [What is same-origin policy](#what-is-same-origin-policy) |
| 96 | [What is the purpose of void 0](#what-is-the-purpose-of-void-0) |
| 97 | [Is JavaScript a compiled or interpreted language](#is-javascript-a-compiled-or-interpreted-language) |
| 98 | [Is JavaScript a case-sensitive language](#is-javascript-a-case-sensitive-language) |
| 99 | [Is there any relation between Java and JavaScript](#is-there-any-relation-between-java-and-javascript) |
| 100 | [What are events](#what-are-events) |
| 101 | [Who created javascript](#who-created-javascript) |
| 102 | [What is the use of preventDefault method](#what-is-the-use-of-preventdefault-method) |
| 103 | [What is the use of stopPropagation method](#what-is-the-use-of-stoppropagation-method) |
| 104 | [What are the steps involved in return false usage](#what-are-the-steps-involved-in-return-false-usage) |
| 105 | [What is BOM](#what-is-bom) |
| 106 | [What is the use of setTimeout](#what-is-the-use-of-settimeout) |
| 107 | [What is the use of setInterval](#what-is-the-use-of-setinterval) |
| 108 | [Why is JavaScript treated as Single threaded](#why-is-javascript-treated-as-single-threaded) |
| 109 | [What is an event delegation](#what-is-an-event-delegation) |
| 110 | [What is ECMAScript](#what-is-ecmascript) |
| 111 | [What is JSON](#what-is-json) |
| 112 | [What are the syntax rules of JSON](#what-are-the-syntax-rules-of-json) |
| 113 | [What is the purpose JSON stringify](#what-is-the-purpose-json-stringify) |
| 114 | [How do you parse JSON string](#how-do-you-parse-json-string) |
| 115 | [Why do you need JSON](#why-do-you-need-json) |
| 116 | [What are PWAs](#what-are-pwas) |
| 117 | [What is the purpose of clearTimeout method](#what-is-the-purpose-of-cleartimeout-method) |
| 118 | [What is the purpose of clearInterval method](#what-is-the-purpose-of-clearinterval-method) |
| 119 | [How do you redirect new page in javascript](#how-do-you-redirect-new-page-in-javascript) |
| 120 | [How do you check whether a string contains a substring](#how-do-you-check-whether-a-string-contains-a-substring) |
| 121 | [How do you validate an email in javascript](#how-do-you-validate-an-email-in-javascript) |
| 122 | [How do you get the current url with javascript](#how-do-you-get-the-current-url-with-javascript) |
| 123 | [What are the various url properties of location object](#what-are-the-various-url-properties-of-location-object) |
| 124 | [How do get query string values in javascript](#how-do-get-query-string-values-in-javascript) |
| 125 | [How do you check if a key exists in an object](#how-do-you-check-if-a-key-exists-in-an-object) |
| 126 | [How do you loop through or enumerate javascript object](#how-do-you-loop-through-or-enumerate-javascript-object) |
| 127 | [How do you test for an empty object](#how-do-you-test-for-an-empty-object) |
| 128 | [What is an arguments object](#what-is-an-arguments-object) |
| 129 | [How do you convert the first letter of a string to uppercase](#how-do-you-make-first-letter-of-the-string-in-an-uppercase) |
| 130 | [What are the pros and cons of for loop](#what-are-the-pros-and-cons-of-for-loop) |
| 131 | [How do you display the current date in javascript](#how-do-you-display-the-current-date-in-javascript) |
| 132 | [How do you compare two date objects](#how-do-you-compare-two-date-objects) |
| 133 | [How do you check if a string starts with another string](#how-do-you-check-if-a-string-starts-with-another-string) |
| 134 | [How do you trim a string in javascript](#how-do-you-trim-a-string-in-javascript) |
| 135 | [How do you add a key value pair in javascript](#how-do-you-add-a-key-value-pair-in-javascript) |
| 136 | [Is the '!--' notation represents a special operator](#is-the----notation-represents-a-special-operator) |
| 137 | [How do you assign default values to variables](#how-do-you-assign-default-values-to-variables) |
| 138 | [How do you define multiline strings](#how-do-you-define-multiline-strings) |
| 139 | [What is an app shell model](#what-is-an-app-shell-model) |
| 140 | [Can we define properties for functions](#can-we-define-properties-for-functions) |
| 141 | [What is the way to find the number of parameters expected by a function](#what-is-the-way-to-find-the-number-of-parameters-expected-by-a-function) |
| 142 | [What is a polyfill](#what-is-a-polyfill) |
| 143 | [What are break and continue statements](#what-are-break-and-continue-statements) |
| 144 | [What are js labels](#what-are-js-labels) |
| 145 | [What are the benefits of keeping declarations at the top](#what-are-the-benefits-of-keeping-declarations-at-the-top) |
| 146 | [What are the benefits of initializing variables](#what-are-the-benefits-of-initializing-variables) |
| 147 | [What are the recommendations to create new object](#what-are-the-recommendations-to-create-new-object) |
| 148 | [How do you define JSON arrays](#how-do-you-define-json-arrays) |
| 149 | [How do you generate random integers](#how-do-you-generate-random-integers) |
| 150 | [Can you write a random integers function to print integers with in a range](#can-you-write-a-random-integers-function-to-print-integers-with-in-a-range) |
| 151 | [What is tree shaking](#what-is-tree-shaking) |
| 152 | [What is the need of tree shaking](#what-is-the-need-of-tree-shaking) |
| 153 | [Is it recommended to use eval](#is-it-recommended-to-use-eval) |
| 154 | [What is a Regular Expression](#what-is-a-regular-expression) |
| 155 | [What are the string methods available in Regular expression](#what-are-the-string-methods-available-in-regular-expression) |
| 156 | [What are modifiers in regular expression](#what-are-modifiers-in-regular-expression) |
| 157 | [What are regular expression patterns](#what-are-regular-expression-patterns) |
| 158 | [What is a RegExp object](#what-is-a-regexp-object) |
| 159 | [How do you search a string for a pattern](#how-do-you-search-a-string-for-a-pattern) |
| 160 | [What is the purpose of exec method](#what-is-the-purpose-of-exec-method) |
| 161 | [How do you change the style of a HTML element](#how-do-you-change-the-style-of-a-html-element) |
| 162 | [What would be the result of 1+2+'3'](#what-would-be-the-result-of-123) |
| 163 | [What is a debugger statement](#what-is-a-debugger-statement) |
| 164 | [What is the purpose of breakpoints in debugging](#what-is-the-purpose-of-breakpoints-in-debugging) |
| 165 | [Can I use reserved words as identifiers](#can-i-use-reserved-words-as-identifiers) |
| 166 | [How do you detect a mobile browser](#how-do-you-detect-a-mobile-browser) |
| 167 | [How do you detect a mobile browser without regexp](#how-do-you-detect-a-mobile-browser-without-regexp) |
| 168 | [How do you get the image width and height using JS](#how-do-you-get-the-image-width-and-height-using-js) |
| 169 | [How do you make synchronous HTTP request](#how-do-you-make-synchronous-http-request) |
| 170 | [How do you make asynchronous HTTP request](#how-do-you-make-asynchronous-http-request) |
| 171 | [How do you convert date to another timezone in javascript](#how-do-you-convert-date-to-another-timezone-in-javascript) |
| 172 | [What are the properties used to get size of window](#what-are-the-properties-used-to-get-size-of-window) |
| 173 | [What is a conditional operator in javascript](#what-is-a-conditional-operator-in-javascript) |
| 174 | [Can you apply chaining on conditional operator](#Can-you-apply-chaining-on-conditional-operator) |
| 175 | [What are the ways to execute javascript after page load](#what-are-the-ways-to-execute-javascript-after-page-load) |
| 176 | [What is the difference between proto and prototype](#what-is-the-difference-between-proto-and-prototype) |
| 177 | [Give an example where do you really need semicolon](#give-an-example-where-do-you-really-need-semicolon) |
| 178 | [What is a freeze method](#what-is-a-freeze-method) |
| 179 | [What is the purpose of freeze method](#what-is-the-purpose-of-freeze-method) |
| 180 | [Why do I need to use freeze method](#why-do-i-need-to-use-freeze-method) |
| 181 | [How do you detect a browser language preference](#how-do-you-detect-a-browser-language-preference) |
| 182 | [How to convert string to title case with javascript](#how-to-convert-string-to-title-case-with-javascript) |
| 183 | [How do you detect javascript disabled in the page](#how-do-you-detect-javascript-disabled-in-the-page) |
| 184 | [What are various operators supported by javascript](#what-are-various-operators-supported-by-javascript) |
| 185 | [What is a rest parameter](#what-is-a-rest-parameter) |
| 186 | [What happens if you do not use rest parameter as a last argument](#what-happens-if-you-do-not-use-rest-parameter-as-a-last-argument) |
| 187 | [What are the bitwise operators available in javascript](#what-are-the-bitwise-operators-available-in-javascript) |
| 188 | [What is a spread operator](#what-is-a-spread-operator) |
| 189 | [How do you determine whether object is frozen or not](#how-do-you-determine-whether-object-is-frozen-or-not) |
| 190 | [How do you determine two values same or not using object](#how-do-you-determine-two-values-same-or-not-using-object) |
| 191 | [What is the purpose of using object is method](#what-is-the-purpose-of-using-object-is-method) |
| 192 | [How do you copy properties from one object to other](#how-do-you-copy-properties-from-one-object-to-other) |
| 193 | [What are the applications of assign method](#what-are-the-applications-of-assign-method) |
| 194 | [What is a proxy object](#what-is-a-proxy-object) |
| 195 | [What is the purpose of seal method](#what-is-the-purpose-of-seal-method) |
| 196 | [What are the applications of seal method](#what-are-the-applications-of-seal-method) |
| 197 | [What are the differences between freeze and seal methods](#what-are-the-differences-between-freeze-and-seal-methods) |
| 198 | [How do you determine if an object is sealed or not](#how-do-you-determine-if-an-object-is-sealed-or-not) |
| 199 | [How do you get enumerable key and value pairs](#how-do-you-get-enumerable-key-and-value-pairs) |
| 200 | [What is the main difference between Object.values and Object.entries method](#what-is-the-main-difference-between-objectvalues-and-objectentries-method) |
| 201 | [How can you get the list of keys of any object](#how-can-you-get-the-list-of-keys-of-any-object) |
| 202 | [How do you create an object with prototype](#how-do-you-create-an-object-with-prototype) |
| 203 | [What is a WeakSet](#what-is-a-weakset) |
| 204 | [What are the differences between a WeakSet and a Set](#what-are-the-differences-between-weakset-and-set) |
| 205 | [List down the collection of methods available on WeakSet](#list-down-the-collection-of-methods-available-on-weakset) |
| 206 | [What is a WeakMap](#what-is-a-weakmap) |
| 207 | [What are the differences between a WeakMap and a Map](#what-are-the-differences-between-weakmap-and-map) |
| 208 | [List down the collection of methods available on WeakMap](#list-down-the-collection-of-methods-available-on-weakmap) |
| 209 | [What is the purpose of uneval](#what-is-the-purpose-of-uneval) |
| 210 | [How do you encode an URL](#how-do-you-encode-an-url) |
| 211 | [How do you decode an URL](#how-do-you-decode-an-url) |
| 212 | [How do you print the contents of web page](#how-do-you-print-the-contents-of-web-page) |
| 213 | [What is the difference between uneval and eval](#what-is-the-difference-between-uneval-and-eval) |
| 214 | [What is an anonymous function](#what-is-an-anonymous-function) |
| 215 | [What is the precedence order between local and global variables](#what-is-the-precedence-order-between-local-and-global-variables) |
| 216 | [What are javascript accessors](#what-are-javascript-accessors) |
| 217 | [How do you define property on Object constructor](#how-do-you-define-property-on-object-constructor) |
| 218 | [What is the difference between get and defineProperty](#what-is-the-difference-between-get-and-defineproperty) |
| 219 | [What are the advantages of Getters and Setters](#what-are-the-advantages-of-getters-and-setters) |
| 220 | [Can I add getters and setters using defineProperty method](#can-i-add-getters-and-setters-using-defineproperty-method) |
| 221 | [What is the purpose of switch-case](#what-is-the-purpose-of-switch-case) |
| 222 | [What are the conventions to be followed for the usage of switch case](#what-are-the-conventions-to-be-followed-for-the-usage-of-switch-case) |
| 223 | [What are primitive data types](#what-are-primitive-data-types) |
| 224 | [What are the different ways to access object properties](#what-are-the-different-ways-to-access-object-properties) |
| 225 | [What are the function parameter rules](#what-are-the-function-parameter-rules) |
| 226 | [What is an error object](#what-is-an-error-object) |
| 227 | [When you get a syntax error](#when-you-get-a-syntax-error) |
| 228 | [What are the different error names from error object](#what-are-the-different-error-names-from-error-object) |
| 229 | [What are the various statements in error handling](#what-are-the-various-statements-in-error-handling) |
| 230 | [What are the two types of loops in javascript](#what-are-the-two-types-of-loops-in-javascript) |
| 231 | [What is nodejs](#what-is-nodejs) |
| 232 | [What is an Intl object](#what-is-an-intl-object) |
| 233 | [How do you perform language specific date and time formatting](#how-do-you-perform-language-specific-date-and-time-formatting) |
| 234 | [What is an Iterator](#what-is-an-iterator) |
| 235 | [How does the synchronous iteration work](#how-does-synchronous-iteration-works) |
| 236 | [What is an event loop](#what-is-an-event-loop) |
| 237 | [What is call stack](#what-is-call-stack) |
| 238 | [What is an event queue](#what-is-an-event-queue) |
| 239 | [What is a decorator](#what-is-a-decorator) |
| 240 | [What are the properties of Intl object](#what-are-the-properties-of-intl-object) |
| 241 | [What is an Unary operator](#what-is-an-unary-operator) |
| 242 | [How do you sort elements in an array](#how-do-you-sort-elements-in-an-array) |
| 243 | [What is the purpose of compareFunction while sorting arrays](#what-is-the-purpose-of-comparefunction-while-sorting-arrays) |
| 244 | [How do you reversing an array](#how-do-you-reversing-an-array) |
| 245 | [How do you find min and max value in an array](#how-do-you-find-min-and-max-value-in-an-array) |
| 246 | [How do you find min and max values without Math functions](#how-do-you-find-min-and-max-values-without-math-functions) |
| 247 | [What is an empty statement and purpose of it](#what-is-an-empty-statement-and-purpose-of-it) |
| 248 | [How do you get metadata of a module](#how-do-you-get-metadata-of-a-module) |
| 249 | [What is a comma operator](#what-is-a-comma-operator) |
| 250 | [What is the advantage of a comma operator](#what-is-the-advantage-of-a-comma-operator) |
| 251 | [What is typescript](#what-is-typescript) |
| 252 | [What are the differences between javascript and typescript](#what-are-the-differences-between-javascript-and-typescript) |
| 253 | [What are the advantages of typescript over javascript](#what-are-the-advantages-of-typescript-over-javascript) |
| 254 | [What is an object initializer](#what-is-an-object-initializer) |
| 255 | [What is a constructor method](#what-is-a-constructor-method) |
| 256 | [What happens if you write constructor more than once in a class](#what-happens-if-you-write-constructor-more-than-once-in-a-class) |
| 257 | [How do you call the constructor of a parent class](#how-do-you-call-the-constructor-of-a-parent-class) |
| 258 | [How do you get the prototype of an object](#how-do-you-get-the-prototype-of-an-object) |
| 259 | [What happens If I pass string type for getPrototype method](#what-happens-if-i-pass-string-type-for-getprototype-method) |
| 260 | [How do you set prototype of one object to another](#how-do-you-set-prototype-of-one-object-to-another) |
| 261 | [How do you check whether an object can be extendable or not](#how-do-you-check-whether-an-object-can-be-extendable-or-not) |
| 262 | [How do you prevent an object to extend](#how-do-you-prevent-an-object-to-extend) |
| 263 | [What are the different ways to make an object non-extensible](#what-are-the-different-ways-to-make-an-object-non-extensible) |
| 264 | [How do you define multiple properties on an object](#how-do-you-define-multiple-properties-on-an-object) |
| 265 | [What is MEAN in javascript](#what-is-mean-in-javascript) |
| 266 | [What Is Obfuscation in javascript](#what-is-obfuscation-in-javascript) |
| 267 | [Why do you need Obfuscation](#why-do-you-need-obfuscation) |
| 268 | [What is Minification](#what-is-minification) |
| 269 | [What are the advantages of minification](#what-are-the-advantages-of-minification) |
| 270 | [What are the differences between Obfuscation and Encryption](#what-are-the-differences-between-obfuscation-and-encryption) |
| 271 | [What are the common tools used for minification](#what-are-the-common-tools-used-for-minification) |
| 272 | [How do you perform form validation using javascript](#how-do-you-perform-form-validation-using-javascript) |
| 273 | [How do you perform form validation without javascript](#how-do-you-perform-form-validation-without-javascript) |
| 274 | [What are the DOM methods available for constraint validation](#what-are-the-dom-methods-available-for-constraint-validation) |
| 275 | [What are the available constraint validation DOM properties](#what-are-the-available-constraint-validation-dom-properties) |
| 276 | [What are the list of validity properties](#what-are-the-list-of-validity-properties) |
| 277 | [Give an example usage of rangeOverflow property](#give-an-example-usage-of-rangeoverflow-property) |
| 278 | [Is enums feature available in javascript](#is-enums-feature-available-in-javascript) |
| 279 | [What is an enum](#What-is-an-enum) |
| 280 | [How do you list all properties of an object](#how-do-you-list-all-properties-of-an-object) |
| 281 | [How do you get property descriptors of an object](#how-do-you-get-property-descriptors-of-an-object) |
| 282 | [What are the attributes provided by a property descriptor](#what-are-the-attributes-provided-by-a-property-descriptor) |
| 283 | [How do you extend classes](#how-do-you-extend-classes) |
| 284 | [How do I modify the url without reloading the page](#how-do-i-modify-the-url-without-reloading-the-page) |
| 285 | [How do you check whether an array includes a particular value or not](#how-do-you-check-whether-an-array-includes-a-particular-value-or-not) |
| 286 | [How do you compare scalar arrays](#how-do-you-compare-scalar-arrays) |
| 287 | [How to get the value from get parameters](#how-to-get-the-value-from-get-parameters) |
| 288 | [How do you print numbers with commas as thousand separators](#how-do-you-print-numbers-with-commas-as-thousand-separators) |
| 289 | [What is the difference between java and javascript](#what-is-the-difference-between-java-and-javascript) |
| 290 | [Does javascript supports namespace](#does-javascript-supports-namespace) |
| 291 | [How do you declare namespace](#how-do-you-declare-namespace) |
| 292 | [How do you invoke javascript code in an iframe from parent page](#how-do-you-invoke-javascript-code-in-an-iframe-from-parent-page) |
| 293 | [How do get the timezone offset from date](#how-do-get-the-timezone-offset-from-date) |
| 294 | [How do you load CSS and JS files dynamically](#how-do-you-load-css-and-js-files-dynamically) |
| 295 | [What are the different methods to find HTML elements in DOM](#what-are-the-different-methods-to-find-html-elements-in-dom) |
| 296 | [What is jQuery](#what-is-jquery) |
| 297 | [What is V8 JavaScript engine](#what-is-v8-javascript-engine) |
| 298 | [Why do we call javascript as dynamic language](#why-do-we-call-javascript-as-dynamic-language) |
| 299 | [What is a void operator](#what-is-a-void-operator) |
| 300 | [How to set the cursor to wait](#how-to-set-the-cursor-to-wait) |
| 301 | [How do you create an infinite loop](#how-do-you-create-an-infinite-loop) |
| 302 | [Why do you need to avoid with statement](#why-do-you-need-to-avoid-with-statement) |
| 303 | [What is the output of below for loops](#what-is-the-output-of-below-for-loops) |
| 304 | [List down some of the features of ES6](#list-down-some-of-the-features-of-es6) |
| 305 | [What is ES6](#what-is-es6) |
| 306 | [Can I redeclare let and const variables](#can-I-redeclare-let-and-const-variables) |
| 307 | [Is const variable makes the value immutable](#is-const-variable-makes-the-value-immutable) |
| 308 | [What are default parameters](#what-are-default-parameters) |
| 309 | [What are template literals](#what-are-template-literals) |
| 310 | [How do you write multi-line strings in template literals](#how-do-you-write-multi-line-strings-in-template-literals) |
| 311 | [What are nesting templates](#what-are-nesting-templates) |
| 312 | [What are tagged templates](#what-are-tagged-templates) |
| 313 | [What are raw strings](#what-are-raw-strings) |
| 314 | [What is destructuring assignment](#what-is-destructuring-assignment) |
| 315 | [What are default values in destructuring assignment](#what-are-default-values-in-destructuring-assignment) |
| 316 | [How do you swap variables in destructuring assignment](#how-do-you-swap-variables-in-destructuring-assignment) |
| 317 | [What are enhanced object literals](#what-are-enhanced-object-literals) |
| 318 | [What are dynamic imports](#what-are-dynamic-imports) |
| 319 | [What are the use cases for dynamic imports](#what-are-the-use-cases-for-dynamic-imports) |
| 320 | [What are typed arrays](#what-are-typed-arrays) |
| 321 | [What are the advantages of module loaders](#what-are-the-advantages-of-module-loaders) |
| 322 | [What is collation](#what-is-collation) |
| 323 | [What is for...of statement](#what-is-forof-statement) |
| 324 | [What is the output of below spread operator array](#what-is-the-output-of-below-spread-operator-array) |
| 325 | [Is PostMessage secure](#is-postmessage-secure) |
| 326 | [What are the problems with postmessage target origin as wildcard](#what-are-the-problems-with-postmessage-target-origin-as-wildcard) |
| 327 | [How do you avoid receiving postMessages from attackers](#how-do-you-avoid-receiving-postmessages-from-attackers) |
| 328 | [Can I avoid using postMessages completely](#can-i-avoid-using-postmessages-completely) |
| 329 | [Is postMessages synchronous](#is-postmessages-synchronous) |
| 330 | [What paradigm is Javascript](#what-paradigm-is-javascript) |
| 331 | [What is the difference between internal and external javascript](#what-is-the-difference-between-internal-and-external-javascript) |
| 332 | [Is JavaScript faster than server side script](#is-javascript-faster-than-server-side-script) |
| 333 | [How do you get the status of a checkbox](#how-do-you-get-the-status-of-a-checkbox) |
| 334 | [What is the purpose of double tilde operator](#what-is-the-purpose-of-double-tilde-operator) |
| 335 | [How do you convert character to ASCII code](#how-do-you-convert-character-to-ascii-code) |
| 336 | [What is ArrayBuffer](#what-is-arraybuffer) |
| 337 | [What is the output of below string expression](#what-is-the-output-of-below-string-expression) |
| 338 | [What is the purpose of Error object](#what-is-the-purpose-of-error-object) |
| 339 | [What is the purpose of EvalError object](#what-is-the-purpose-of-evalerror-object) |
| 340 | [What are the list of cases error thrown from non-strict mode to strict mode](#what-are-the-list-of-cases-error-thrown-from-non-strict-mode-to-strict-mode) |
| 341 | [Do all objects have prototypes](#do-all-objects-have-prototypes) |
| 342 | [What is the difference between a parameter and an argument](#what-is-the-difference-between-a-parameter-and-an-argument) |
| 343 | [What is the purpose of some method in arrays](#what-is-the-purpose-of-some-method-in-arrays) |
| 344 | [How do you combine two or more arrays](#how-do-you-combine-two-or-more-arrays) |
| 345 | [What is the difference between Shallow and Deep copy](#what-is-the-difference-between-shallow-and-deep-copy) |
| 346 | [How do you create specific number of copies of a string](#how-do-you-create-specific-number-of-copies-of-a-string) |
| 347 | [How do you return all matching strings against a regular expression](#how-do-you-return-all-matching-strings-against-a-regular-expression) |
| 348 | [How do you trim a string at the beginning or ending](#how-do-you-trim-a-string-at-the-beginning-or-ending) |
| 349 | [What is the output of below console statement with unary operator](#what-is-the-output-of-below-console-statement-with-unary-operator) |
| 350 | [Does javascript uses mixins](#does-javascript-uses-mixins) |
| 351 | [What is a thunk function](#what-is-a-thunk-function) |
| 352 | [What are asynchronous thunks](#what-are-asynchronous-thunks) |
| 353 | [What is the output of below function calls](#what-is-the-output-of-below-function-calls) |
| 354 | [How to remove all line breaks from a string](#how-to-remove-all-line-breaks-from-a-string) |
| 355 | [What is the difference between reflow and repaint](#what-is-the-difference-between-reflow-and-repaint) |
| 356 | [What happens with negating an array](#what-happens-with-negating-an-array) |
| 357 | [What happens if we add two arrays](#what-happens-if-we-add-two-arrays) |
| 358 | [What is the output of prepend additive operator on falsy values](#what-is-the-output-of-prepend-additive-operator-on-falsy-values) |
| 359 | [How do you create self string using special characters](#how-do-you-create-self-string-using-special-characters) |
| 360 | [How do you remove falsy values from an array](#how-do-you-remove-falsy-values-from-an-array) |
| 361 | [How do you get unique values of an array](#how-do-you-get-unique-values-of-an-array) |
| 362 | [What is destructuring aliases](#what-is-destructuring-aliases) |
| 363 | [How do you map the array values without using map method](#how-do-you-map-the-array-values-without-using-map-method) |
| 364 | [How do you empty an array](#how-do-you-empty-an-array) |
| 365 | [How do you round numbers to certain decimals](#how-do-you-rounding-numbers-to-certain-decimals) |
| 366 | [What is the easiest way to convert an array to an object](#what-is-the-easiest-way-to-convert-an-array-to-an-object) |
| 367 | [How do you create an array with some data](#how-do-you-create-an-array-with-some-data) |
| 368 | [What are the placeholders from console object](#what-are-the-placeholders-from-console-object) |
| 369 | [Is it possible to add CSS to console messages](#is-it-possible-to-add-css-to-console-messages) |
| 370 | [What is the purpose of dir method of console object](#what-is-the-purpose-of-dir-method-of-console-object) |
| 371 | [Is it possible to debug HTML elements in console](#is-it-possible-to-debug-html-elements-in-console) |
| 372 | [How do you display data in a tabular format using console object](#how-do-you-display-data-in-a-tabular-format-using-console-object) |
| 373 | [How do you verify that an argument is a Number or not](#how-do-you-verify-that-an-argument-is-a-number-or-not) |
| 374 | [How do you create copy to clipboard button](#how-do-you-create-copy-to-clipboard-button) |
| 375 | [What is the shortcut to get timestamp](#what-is-the-shortcut-to-get-timestamp) |
| 376 | [How do you flattening multi dimensional arrays](#how-do-you-flattening-multi-dimensional-arrays) |
| 377 | [What is the easiest multi condition checking](#what-is-the-easiest-multi-condition-checking) |
| 378 | [How do you capture browser back button](#how-do-you-capture-browser-back-button) |
| 379 | [How do you disable right click in the web page](#how-do-you-disable-right-click-in-the-web-page) |
| 380 | [What are wrapper objects](#what-are-wrapper-objects) |
| 381 | [What is AJAX](#what-is-ajax) |
| 382 | [What are the different ways to deal with Asynchronous Code](#what-are-the-different-ways-to-deal-with-asynchronous-code) |
| 383 | [How to cancel a fetch request](#how-to-cancel-a-fetch-request) |
| 384 | [What is web speech API](#what-is-web-speech-api) |
| 385 | [What is minimum timeout throttling](#what-is-minimum-timeout-throttling) |
| 386 | [How do you implement zero timeout in modern browsers](#how-do-you-implement-zero-timeout-in-modern-browsers) |
| 387 | [What are tasks in event loop](#what-are-tasks-in-event-loop) |
| 388 | [What is microtask](#what-is-microtask) |
| 389 | [What are different event loops](#what-are-different-event-loops) |
| 390 | [What is the purpose of queueMicrotask](#what-is-the-purpose-of-queuemicrotask) |
| 391 | [How do you use javascript libraries in typescript file](#how-do-you-use-javascript-libraries-in-typescript-file) |
| 392 | [What are the differences between promises and observables](#what-are-the-differences-between-promises-and-observables) |
| 393 | [What is heap](#what-is-heap) |
| 394 | [What is an event table](#what-is-an-event-table) |
| 395 | [What is a microTask queue](#what-is-a-microtask-queue) |
| 396 | [What is the difference between shim and polyfill](#what-is-the-difference-between-shim-and-polyfill) |
| 397 | [How do you detect primitive or non primitive value type](#how-do-you-detect-primitive-or-non-primitive-value-type) |
| 398 | [What is babel](#what-is-babel) |
| 399 | [Is Node.js completely single threaded](#is-nodejs-completely-single-threaded) |
| 400 | [What are the common use cases of observables](#what-are-the-common-use-cases-of-observables) |
| 401 | [What is RxJS](#what-is-rxjs) |
| 402 | [What is the difference between Function constructor and function declaration](#what-is-the-difference-between-function-constructor-and-function-declaration) |
| 403 | [What is a Short circuit condition](#what-is-a-short-circuit-condition) |
| 404 | [What is the easiest way to resize an array](#what-is-the-easiest-way-to-resize-an-array) |
| 405 | [What is an observable](#what-is-an-observable) |
| 406 | [What is the difference between function and class declarations](#what-is-the-difference-between-function-and-class-declarations) |
| 407 | [What is an async function](#what-is-an-async-function) |
| 408 | [How do you prevent promises swallowing errors](#how-do-you-prevent-promises-swallowing-errors) |
| 409 | [What is deno](#what-is-deno) |
| 410 | [How do you make an object iterable in javascript](#how-do-you-make-an-object-iterable-in-javascript) |
| 411 | [What is a Proper Tail Call](#what-is-a-proper-tail-call) |
| 412 | [How do you check an object is a promise or not](#how-do-you-check-an-object-is-a-promise-or-not) |
| 413 | [How to detect if a function is called as constructor](#how-to-detect-if-a-function-is-called-as-constructor) |
| 414 | [What are the differences between arguments object and rest parameter](#what-are-the-differences-between-arguments-object-and-rest-parameter) |
| 415 | [What are the differences between spread operator and rest parameter](#what-are-the-differences-between-spread-operator-and-rest-parameter) |
| 416 | [What are the different kinds of generators](#what-are-the-different-kinds-of-generators) |
| 417 | [What are the built-in iterables](#what-are-the-built-in-iterables) |
| 418 | [What are the differences between for...of and for...in statements](#what-are-the-differences-between-forof-and-forin-statements) |
| 419 | [How do you define instance and non-instance properties](#how-do-you-define-instance-and-non-instance-properties) |
| 420 | [What is the difference between isNaN and Number.isNaN?](#what-is-the-difference-between-isnan-and-numberisnan) |
| 421 | [How to invoke an IIFE without any extra brackets?](#how-to-invoke-an-iife-without-any-extra-brackets) |
| 422 | [Is that possible to use expressions in switch cases?](#is-that-possible-to-use-expressions-in-switch-cases) |
| 423 | [What is the easiest way to ignore promise errors?](#what-is-the-easiest-way-to-ignore-promise-errors) |
| 424 | [How do style the console output using CSS?](#how-do-style-the-console-output-using-css) |
| 425 | [What is nullish coalescing operator (??)?](#what-is-nullish-coalescing-operator) |
| 426 | [How do you group and nest console output?](#how-do-you-group-and-nest-console-output) |
| 427 | [What is the difference between dense and sparse arrays?](#what-is-the-difference-between-dense-and-sparse-arrays) |
| 428 | [What are the different ways to create sparse arrays?](#what-are-the-different-ways-to-create-sparse-arrays) |
| 429 | [What is the difference between setTimeout, setImmediate and process.nextTick?](#what-is-the-difference-between-settimeout-setimmediate-and-processnexttick) |
| 430 | [How do you reverse an array without modifying original array?](#how-do-you-reverse-an-array-without-modifying-original-array) |
| 431 | [How do you create custom HTML element?](#how-do-you-create-custom-html-element) |
| 432 | [What is global execution context?](#what-is-global-execution-context) |
| 433 | [What is function execution context?](#what-is-function-execution-context) |
| 434 | [What is debouncing?](#what-is-debouncing) |
| 435 | [What is throttling?](#what-is-throttling) |
| 436 | [What is optional chaining?](#what-is-optional-chaining) |
| 437 | [What is an environment record?](#what-is-an-environment-record) |
| 438 | [How to verify if a variable is an array?](#how-to-verify-if-a-variable-is-an-array) |
| 439 | [What is pass by value and pass by reference?](#what-is-pass-by-value-and-pass-by-reference) |
| 440 | [What are the differences between primitives and non-primitives?](#what-are-the-differences-between-primitives-and-non-primitives) |
| 441 | [What are hidden classes?](#what-are-hidden-classes) |
| 442 | [What is inline caching?](#what-is-inline-caching) |
| 443 | [How do you create your own bind method using either call or apply method?](#how-do-you-create-your-own-bind-method-using-either-call-or-apply-method) |
| 444 | [What are the differences between pure and impure functions?](#what-are-the-differences-between-pure-and-impure-functions?) |
| 445 | [What is referential transparency?](#what-is-referential-transparency) |
| 446 | [What are the possible side-effects in javascript?](#what-are-the-possible-side-effects-in-javascript) |
| 447 | [What are compose and pipe functions?](#what-are-compose-and-pipe-functions) |
| 448 | [What is module pattern?](#what-is-module-pattern) |
| 449 | [What is Function Composition?](#what-is-function-composition) |
| 450 | [How to use await outside of async function prior to ES2022?](#how-to-use-await-outside-of-async-function-prior-to-es2022) |
| 451 | [What is the purpose of the this keyword in JavaScript?](#what_is_the_purpose_of_the_this_keyword_in_javascript?) |
1. ### What are the possible ways to create objects in JavaScript
There are many ways to create objects in javascript as mentioned below:
1. **Object literal syntax:**
The object literal syntax (or object initializer), is a comma-separated set of name-value pairs wrapped in curly braces.
```javascript
var object = {
name: "Sudheer",
age: 34
};
```
Object literal property values can be of any data type, including array, function, and nested object.
**Note:** This is one of the easiest ways to create an object.
2. **Object constructor:**
The simplest way to create an empty object is using the `Object` constructor. Currently this approach is not recommended.
```javascript
var object = new Object();
```
The `Object()` is a built-in constructor function so "new" keyword is not required. The above code snippet can be re-written as:
```javascript
var object = Object();
```
3. **Object's create method:**
The `create` method of Object is used to create a new object by passing the specificied prototype object and properties as arguments, i.e., this pattern is helpful to create new objects based on existing objects.
The second argument is optional and it is used to create properties on a newly created object.
The following code creates a new empty object whose prototype is null.
```javascript
var object = Object.create(null);
```
The following example creates an object along with additional new properties.
```javascript
let vehicle = {
wheels: '4',
fuelType: 'Gasoline',
color: 'Green'
}
let carProps = {
type: {
value: 'Volkswagen'
},
model: {
value: 'Golf'
}
}
var car = Object.create(vehicle, carProps);
console.log(car);
```
4. **Function constructor:**
In this approach, create any function and apply the new operator to create object instances.
```javascript
function Person(name) {
this.name = name;
this.age = 21;
}
var object = new Person("Sudheer");
```
5. **Function constructor with prototype:**
This is similar to function constructor but it uses prototype for their properties and methods,
```javascript
function Person() {}
Person.prototype.name = "Sudheer";
var object = new Person();
```
This is equivalent to creating an instance with Object.create method with a function prototype and then calling that function with an instance and parameters as arguments.
```javascript
function func() {}
new func(x, y, z);
```
**(OR)**
```javascript
// Create a new instance using function prototype.
var newInstance = Object.create(func.prototype)
// Call the function
var result = func.call(newInstance, x, y, z),
// If the result is a non-null object then use it otherwise just use the new instance.
console.log(result && typeof result === 'object' ? result : newInstance);
```
6. **Object's assign method:**
The `Object.assign` method is used to copy all the properties from one or more source objects and stores them into a target object.
The following code creates a new staff object by copying properties of his working company and the car he owns.
```javascript
const orgObject = { company: 'XYZ Corp'};
const carObject = { name: 'Toyota'};
const staff = Object.assign({}, orgObject, carObject);
```
7. **ES6 Class syntax:**
ES6 introduces class feature to create objects.
```javascript
class Person {
constructor(name) {
this.name = name;
}
}
var object = new Person("Sudheer");
```
8. **Singleton pattern:**
A Singleton is an object which can only be instantiated one time. Repeated calls to its constructor return the same instance. This way one can ensure that they don't accidentally create multiple instances.
```javascript
var object = new (function () {
this.name = "Sudheer";
})();
```
**[⬆ Back to Top](#table-of-contents)**
2. ### What is a prototype chain
**Prototype chaining** is used to build new types of objects based on existing ones. It is similar to inheritance in a class based language.
The prototype on object instance is available through **Object.getPrototypeOf(object)** or **\_\_proto\_\_** property whereas prototype on constructors function is available through **Object.prototype**.
**[⬆ Back to Top](#table-of-contents)**
3. ### What is the difference between Call, Apply and Bind
The difference between Call, Apply and Bind can be explained with below examples,
**Call:** The call() method invokes a function with a given `this` value and arguments provided one by one
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
invite.call(employee1, "Hello", "How are you?"); // Hello John Rodson, How are you?
invite.call(employee2, "Hello", "How are you?"); // Hello Jimmy Baily, How are you?
```
**Apply:** Invokes the function with a given `this` value and allows you to pass in arguments as an array
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
invite.apply(employee1, ["Hello", "How are you?"]); // Hello John Rodson, How are you?
invite.apply(employee2, ["Hello", "How are you?"]); // Hello Jimmy Baily, How are you?
```
**Bind:** returns a new function, allowing you to pass any number of arguments
```javascript
var employee1 = { firstName: "John", lastName: "Rodson" };
var employee2 = { firstName: "Jimmy", lastName: "Baily" };
function invite(greeting1, greeting2) {
console.log(
greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
);
}
var inviteEmployee1 = invite.bind(employee1);
var inviteEmployee2 = invite.bind(employee2);
inviteEmployee1("Hello", "How are you?"); // Hello John Rodson, How are you?
inviteEmployee2("Hello", "How are you?"); // Hello Jimmy Baily, How are you?
```
Call and Apply are pretty much interchangeable. Both execute the current function immediately. You need to decide whether it’s easier to send in an array or a comma separated list of arguments. You can remember by treating Call is for **comma** (separated list) and Apply is for **Array**.
Bind creates a new function that will have `this` set to the first parameter passed to bind().
**[⬆ Back to Top](#table-of-contents)**
4. ### What is JSON and its common operations
**JSON** is a text-based data format following JavaScript object syntax, which was popularized by `Douglas Crockford`. It is useful when you want to transmit data across a network. It is basically just a text file with an extension of .json, and a MIME type of application/json
**Parsing:** Converting a string to a native object
```javascript
JSON.parse(text);
```
**Stringification:** Converting a native object to a string so that it can be transmitted across the network
```javascript
JSON.stringify(object);
```
**[⬆ Back to Top](#table-of-contents)**
5. ### What is the purpose of the array slice method
The **slice()** method returns the selected elements in an array as a new array object. It selects the elements starting at the given start argument, and ends at the given optional end argument without including the last element. If you omit the second argument then it selects till the end of the array.
Some of the examples of this method are,
```javascript
let arrayIntegers = [1, 2, 3, 4, 5];
let arrayIntegers1 = arrayIntegers.slice(0, 2); // returns [1,2]
let arrayIntegers2 = arrayIntegers.slice(2, 3); // returns [3]
let arrayIntegers3 = arrayIntegers.slice(4); //returns [5]
```
**Note:** Slice method doesn't mutate the original array but it returns the subset as a new array.
**[⬆ Back to Top](#table-of-contents)**
6. ### What is the purpose of the array splice method
The **splice()** method adds/removes items to/from an array, and then returns the removed item. The first argument specifies the array position/index for insertion or deletion whereas the optional second argument indicates the number of elements to be deleted. Each additional argument is added to the array.
Some of the examples of this method are:
```javascript
let arrayIntegersOriginal1 = [1, 2, 3, 4, 5];
let arrayIntegersOriginal2 = [1, 2, 3, 4, 5];
let arrayIntegersOriginal3 = [1, 2, 3, 4, 5];
let arrayIntegers1 = arrayIntegersOriginal1.splice(0, 2); // returns [1, 2]; original array: [3, 4, 5]
let arrayIntegers2 = arrayIntegersOriginal2.splice(3); // returns [4, 5]; original array: [1, 2, 3]
let arrayIntegers3 = arrayIntegersOriginal3.splice(3, 1, "a", "b", "c"); //returns [4]; original array: [1, 2, 3, "a", "b", "c", 5]
```
**Note:** Splice method modifies the original array and returns the deleted array.
**[⬆ Back to Top](#table-of-contents)**
7. ### What is the difference between slice and splice
Some of the major differences in a tabular form:
| Slice | Splice |
| -------------------------------------------- | ----------------------------------------------- |
| Doesn't modify the original array(immutable) | Modifies the original array(mutable) |
| Returns the subset of original array | Returns the deleted elements as array |
| Used to pick the elements from array | Used to insert/delete elements to/from array |
**[⬆ Back to Top](#table-of-contents)**
8. ### How do you compare Object and Map
**Objects** are similar to **Maps** in that both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a key. Due to this reason, Objects have been used as Maps historically. But there are important differences that make using a Map preferable in certain cases:
1. The keys of an Object can be Strings and Symbols, whereas they can be any value for a Map, including functions, objects, and any primitive.
2. The keys in a Map are ordered while keys added to Object are not. Thus, when iterating over it, a Map object returns keys in the order of insertion.
3. You can get the size of a Map easily with the size property, while the number of properties in an Object must be determined manually.
4. A Map is an iterable and can thus be directly iterated, whereas iterating over an Object requires obtaining its keys in some fashion and iterating over them.
5. An Object has a prototype, so there are default keys in an object that could collide with your keys if you're not careful. As of ES5 this can be bypassed by creating an object(which can be called a map) using `Object.create(null)`, but this practice is seldom done.
6. A Map may perform better in scenarios involving frequent addition and removal of key pairs.
**[⬆ Back to Top](#table-of-contents)**
9. ### What is the difference between == and === operators
JavaScript provides both strict(===, !==) and type-converting(==, !=) equality comparison. The strict operators take type of variable in consideration, while non-strict operators make type correction/conversion based upon values of variables. The strict operators follow the below conditions for different types,
1. Two strings are strictly equal when they have the same sequence of characters, same length, and same characters in corresponding positions.
2. Two numbers are strictly equal when they are numerically equal, i.e., having the same number value.
There are two special cases in this,
1. NaN is not equal to anything, including NaN.
2. Positive and negative zeros are equal to one another.
3. Two Boolean operands are strictly equal if both are true or both are false.
4. Two objects are strictly equal if they refer to the same Object.
5. Null and Undefined types are not equal with ===, but equal with == .
i.e, `null===undefined --> false`, but `null==undefined --> true`
Some of the example which covers the above cases:
```javascript
0 == false // true
0 === false // false
1 == "1" // true
1 === "1" // false
null == undefined // true
null === undefined // false
'0' == false // true
'0' === false // false
NaN == NaN or NaN === NaN // false
[]==[] or []===[] //false, refer different objects in memory
{}=={} or {}==={} //false, refer different objects in memory
```
**[⬆ Back to Top](#table-of-contents)**
10. ### What are lambda expressions or arrow functions
An arrow function is a shorter/concise syntax for a function expression and does not have its own **this, arguments, super, or new.target**. These functions are best suited for non-method functions, and they cannot be used as constructors.
Some of the examples of arrow functions are listed as below,
```javascript
const arrowFunc1 = (a, b) => a + b; // Multiple parameters
const arrowFunc2 = a => a * 10; // Single parameter
const arrowFunc3 = () => {} // no parameters
```
**[⬆ Back to Top](#table-of-contents)**
11. ### What is a first class function
In Javascript, functions are first class objects. First-class functions means when functions in that language are treated like any other variable.
For example, in such a language, a function can be passed as an argument to other functions, can be returned by another function and can be assigned as a value to a variable. For example, in the below example, handler functions assigned to a listener
```javascript
const handler = () => console.log("This is a click handler function");
document.addEventListener("click", handler);
```
**[⬆ Back to Top](#table-of-contents)**
12. ### What is a first order function
A first-order function is a function that doesn’t accept another function as an argument and doesn’t return a function as its return value.
```javascript
const firstOrder = () => console.log("I am a first order function!");
```
**[⬆ Back to Top](#table-of-contents)**
13. ### What is a higher order function
A higher-order function is a function that accepts another function as an argument or returns a function as a return value or both.
```javascript
const firstOrderFunc = () =>
console.log("Hello, I am a First order function");
const higherOrder = (ReturnFirstOrderFunc) => ReturnFirstOrderFunc();
higherOrder(firstOrderFunc);
```
**[⬆ Back to Top](#table-of-contents)**
14. ### What is a unary function
A unary function (i.e. monadic) is a function that accepts exactly one argument. It stands for a single argument accepted by a function.
Let us take an example of unary function,
```javascript
const unaryFunction = (a) => console.log(a + 10); // Add 10 to the given argument and display the value
```
**[⬆ Back to Top](#table-of-contents)**
15. ### What is the currying function
Currying is the process of taking a function with multiple arguments and turning it into a sequence of functions each with only a single argument. Currying is named after a mathematician **Haskell Curry**. By applying currying, an n-ary function turns into a unary function.
Let's take an example of n-ary function and how it turns into a currying function,
```javascript
const multiArgFunction = (a, b, c) => a + b + c;
console.log(multiArgFunction(1, 2, 3)); // 6
const curryUnaryFunction = (a) => (b) => (c) => a + b + c;
curryUnaryFunction(1); // returns a function: b => c => 1 + b + c
curryUnaryFunction(1)(2); // returns a function: c => 3 + c
curryUnaryFunction(1)(2)(3); // returns the number 6
```
Curried functions are great to improve **code reusability** and **functional composition**.
**[⬆ Back to Top](#table-of-contents)**
16. ### What is a pure function
A **Pure function** is a function where the return value is only determined by its arguments without any side effects. i.e, If you call a function with the same arguments 'n' number of times and 'n' number of places in the application then it will always return the same value.
Let's take an example to see the difference between pure and impure functions,
```javascript
//Impure
let numberArray = [];
const impureAddNumber = (number) => numberArray.push(number);
//Pure
const pureAddNumber = (number) => (argNumberArray) =>
argNumberArray.concat([number]);
//Display the results
console.log(impureAddNumber(6)); // returns 1
console.log(numberArray); // returns [6]
console.log(pureAddNumber(7)(numberArray)); // returns [6, 7]
console.log(numberArray); // returns [6]
```
As per the above code snippets, the **Push** function is impure itself by altering the array and returning a push number index independent of the parameter value, whereas **Concat** on the other hand takes the array and concatenates it with the other array producing a whole new array without side effects. Also, the return value is a concatenation of the previous array.
Remember that Pure functions are important as they simplify unit testing without any side effects and no need for dependency injection. They also avoid tight coupling and make it harder to break your application by not having any side effects. These principles are coming together with the **Immutability** concept of ES6: giving preference to **const** over **let** usage.
**[⬆ Back to Top](#table-of-contents)**
17. ### What is the purpose of the let keyword
The `let` statement declares a **block scope local variable**. Hence the variables defined with let keyword are limited in scope to the block, statement, or expression on which it is used. Whereas variables declared with the `var` keyword used to define a variable globally, or locally to an entire function regardless of block scope.
Let's take an example to demonstrate the usage,
```javascript
let counter = 30;
if (counter === 30) {
let counter = 31;
console.log(counter); // 31
}
console.log(counter); // 30 (because the variable in if block won't exist here)
```
**[⬆ Back to Top](#table-of-contents)**
18. ### What is the difference between let and var
You can list out the differences in a tabular format
| var | let |
| ----------------------------------------------------- | --------------------------- |
| It has been available from the beginning of JavaScript | Introduced as part of ES6 |
| It has function scope | It has block scope |
| Variable declaration will be hoisted | Hoisted but not initialized |
| It is possible to re-declare the variable in the same scope | It is not possible to re-declare the variable |
Let's take an example to see the difference,
```javascript
function userDetails(username) {
if (username) {
console.log(salary); // undefined due to hoisting
console.log(age); // ReferenceError: Cannot access 'age' before initialization
let age = 30;
var salary = 10000;
}
console.log(salary); //10000 (accessible due to function scope)
console.log(age); //error: age is not defined(due to block scope)
}
userDetails("John");
```
**[⬆ Back to Top](#table-of-contents)**
19. ### What is the reason to choose the name let as a keyword
`let` is a mathematical statement that was adopted by early programming languages like **Scheme** and **Basic**. It has been borrowed from dozens of other languages that use `let` already as a traditional keyword as close to `var` as possible.
**[⬆ Back to Top](#table-of-contents)**
20. ### How do you redeclare variables in a switch block without an error
If you try to redeclare variables in a `switch block` then it will cause errors because there is only one block. For example, the below code block throws a syntax error as below,
```javascript
let counter = 1;
switch (x) {
case 0:
let name;
break;
case 1:
let name; // SyntaxError for redeclaration.
break;
}
```
To avoid this error, you can create a nested block inside a case clause and create a new block scoped lexical environment.
```javascript
let counter = 1;
switch (x) {
case 0: {
let name;
break;
}
case 1: {
let name; // No SyntaxError for redeclaration.
break;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
21. ### What is the Temporal Dead Zone
The Temporal Dead Zone(TDZ) is a specific period or area of a block where a variable is inaccessible until it has been intialized with a value. This behavior in JavaScript that occurs when declaring a variable with the let and const keywords, but not with var. In ECMAScript 6, accessing a `let` or `const` variable before its declaration (within its scope) causes a ReferenceError.
Let's see this behavior with an example,
```javascript
function somemethod() {
console.log(counter1); // undefined
console.log(counter2); // ReferenceError
var counter1 = 1;
let counter2 = 2;
}
```
**[⬆ Back to Top](#table-of-contents)**
22. ### What is an IIFE (Immediately Invoked Function Expression)
IIFE (Immediately Invoked Function Expression) is a JavaScript function that runs as soon as it is defined. The signature of it would be as below,
```javascript
(function () {
// logic here
})();
```
The primary reason to use an IIFE is to obtain data privacy because any variables declared within the IIFE cannot be accessed by the outside world. i.e, If you try to access variables from the IIFE then it throws an error as below,
```javascript
(function () {
var message = "IIFE";
console.log(message);
})();
console.log(message); //Error: message is not defined
```
**[⬆ Back to Top](#table-of-contents)**
23. ### How do you decode or encode a URL in JavaScript?
`encodeURI()` function is used to encode an URL. This function requires a URL string as a parameter and return that encoded string.
`decodeURI()` function is used to decode an URL. This function requires an encoded URL string as parameter and return that decoded string.
**Note:** If you want to encode characters such as `/ ? : @ & = + $ #` then you need to use `encodeURIComponent()`.
```javascript
let uri = "employeeDetails?name=john&occupation=manager";
let encoded_uri = encodeURI(uri);
let decoded_uri = decodeURI(encoded_uri);
```
**[⬆ Back to Top](#table-of-contents)**
24. ### What is memoization
Memoization is a functional programming technique which attempts to increase a function’s performance by caching its previously computed results. Each time a memoized function is called, its parameters are used to index the cache. If the data is present, then it can be returned, without executing the entire function. Otherwise the function is executed and then the result is added to the cache.
Let's take an example of adding function with memoization,
```javascript
const memoizAddition = () => {
let cache = {};
return (value) => {
if (value in cache) {
console.log("Fetching from cache");
return cache[value]; // Here, cache.value cannot be used as property name starts with the number which is not a valid JavaScript identifier. Hence, can only be accessed using the square bracket notation.
} else {
console.log("Calculating result");
let result = value + 20;
cache[value] = result;
return result;
}
};
};
// returned function from memoizAddition
const addition = memoizAddition();
console.log(addition(20)); //output: 40 calculated
console.log(addition(20)); //output: 40 cached
```
**[⬆ Back to Top](#table-of-contents)**
25. ### What is Hoisting
Hoisting is a JavaScript mechanism where variables, function declarations and classes are moved to the top of their scope before code execution. Remember that JavaScript only hoists declarations, not initialisation.
Let's take a simple example of variable hoisting,
```javascript
console.log(message); //output : undefined
var message = "The variable Has been hoisted";
```
The above code looks like as below to the interpreter,
```javascript
var message;
console.log(message);
message = "The variable Has been hoisted";
```
In the same fashion, function declarations are hoisted too
```javascript
message("Good morning"); //Good morning
function message(name) {
console.log(name);
}
```
This hoisting makes functions to be safely used in code before they are declared.
**[⬆ Back to Top](#table-of-contents)**
26. ### What are classes in ES6
In ES6, Javascript classes are primarily syntactic sugar over JavaScript’s existing prototype-based inheritance.
For example, the prototype based inheritance written in function expression as below,
```javascript
function Bike(model, color) {
this.model = model;
this.color = color;
}
Bike.prototype.getDetails = function () {
return this.model + " bike has" + this.color + " color";
};
```
Whereas ES6 classes can be defined as an alternative
```javascript
class Bike {
constructor(color, model) {
this.color = color;
this.model = model;
}
getDetails() {
return this.model + " bike has" + this.color + " color";
}
}
```
**[⬆ Back to Top](#table-of-contents)**
27. ### What are closures
A closure is the combination of a function and the lexical environment within which that function was declared. i.e, It is an inner function that has access to the outer or enclosing function’s variables, functions and other data even after the outer function has finished its execution. The closure has three scope chains.
1. Own scope where variables defined between its curly brackets
2. Outer function’s variables
3. Global variables
Let's take an example of closure concept,
```javascript
function Welcome(name) {
var greetingInfo = function (message) {
console.log(message + " " + name);
};
return greetingInfo;
}
var myFunction = Welcome("John");
myFunction("Welcome "); //Output: Welcome John
myFunction("Hello Mr."); //output: Hello Mr. John
```
As per the above code, the inner function(i.e, greetingInfo) has access to the variables in the outer function scope(i.e, Welcome) even after the outer function has returned.
**[⬆ Back to Top](#table-of-contents)**
28. ### What are modules
Modules refer to small units of independent, reusable code and also act as the foundation of many JavaScript design patterns. Most of the JavaScript modules export an object literal, a function, or a constructor
**[⬆ Back to Top](#table-of-contents)**
29. ### Why do you need modules
Below are the list of benefits using modules in javascript ecosystem
1. Maintainability
2. Reusability
3. Namespacing
**[⬆ Back to Top](#table-of-contents)**
30. ### What is scope in javascript
Scope is the accessibility of variables, functions, and objects in some particular part of your code during runtime. In other words, scope determines the visibility of variables and other resources in areas of your code.
**[⬆ Back to Top](#table-of-contents)**
31. ### What is a service worker
A Service worker is basically a script (JavaScript file) that runs in the background, separate from a web page and provides features that don't need a web page or user interaction. Some of the major features of service workers are Rich offline experiences(offline first web application development), periodic background syncs, push notifications, intercept and handle network requests and programmatically managing a cache of responses.
**[⬆ Back to Top](#table-of-contents)**
32. ### How do you manipulate DOM using a service worker
Service worker can't access the DOM directly. But it can communicate with the pages it controls by responding to messages sent via the `postMessage` interface, and those pages can manipulate the DOM.
**[⬆ Back to Top](#table-of-contents)**
33. ### How do you reuse information across service worker restarts
The problem with service worker is that it gets terminated when not in use, and restarted when it's next needed, so you cannot rely on global state within a service worker's `onfetch` and `onmessage` handlers. In this case, service workers will have access to IndexedDB API in order to persist and reuse across restarts.
**[⬆ Back to Top](#table-of-contents)**
34. ### What is IndexedDB
IndexedDB is a low-level API for client-side storage of larger amounts of structured data, including files/blobs. This API uses indexes to enable high-performance searches of this data.
**[⬆ Back to Top](#table-of-contents)**
35. ### What is web storage
Web storage is an API that provides a mechanism by which browsers can store key/value pairs locally within the user's browser, in a much more intuitive fashion than using cookies. The web storage provides two mechanisms for storing data on the client.
1. **Local storage:** It stores data for current origin with no expiration date.
2. **Session storage:** It stores data for one session and the data is lost when the browser tab is closed.
**[⬆ Back to Top](#table-of-contents)**
36. ### What is a post message
Post message is a method that enables cross-origin communication between Window objects.(i.e, between a page and a pop-up that it spawned, or between a page and an iframe embedded within it). Generally, scripts on different pages are allowed to access each other if and only if the pages follow same-origin policy(i.e, pages share the same protocol, port number, and host).
**[⬆ Back to Top](#table-of-contents)**
37. ### What is a Cookie
A cookie is a piece of data that is stored on your computer to be accessed by your browser. Cookies are saved as key/value pairs.
For example, you can create a cookie named username as below,
```javascript
document.cookie = "username=John";
```
**[⬆ Back to Top](#table-of-contents)**
38. ### Why do you need a Cookie
Cookies are used to remember information about the user profile(such as username). It basically involves two steps,
1. When a user visits a web page, the user profile can be stored in a cookie.
2. Next time the user visits the page, the cookie remembers the user profile.
**[⬆ Back to Top](#table-of-contents)**
39. ### What are the options in a cookie
There are few below options available for a cookie,
1. By default, the cookie is deleted when the browser is closed but you can change this behavior by setting expiry date (in UTC time).
```javascript
document.cookie = "username=John; expires=Sat, 8 Jun 2019 12:00:00 UTC";
```
1. By default, the cookie belongs to a current page. But you can tell the browser what path the cookie belongs to using a path parameter.
```javascript
document.cookie = "username=John; path=/services";
```
**[⬆ Back to Top](#table-of-contents)**
40. ### How do you delete a cookie
You can delete a cookie by setting the expiry date as a passed date. You don't need to specify a cookie value in this case.
For example, you can delete a username cookie in the current page as below.
```javascript
document.cookie =
"username=; expires=Fri, 07 Jun 2019 00:00:00 UTC; path=/;";
```
**Note:** You should define the cookie path option to ensure that you delete the right cookie. Some browsers doesn't allow to delete a cookie unless you specify a path parameter.
**[⬆ Back to Top](#table-of-contents)**
41. ### What are the differences between cookie, local storage and session storage
Below are some of the differences between cookie, local storage and session storage,
| Feature | Cookie | Local storage | Session storage |
| --------------------------------- | ---------------------------------- | ---------------- | ------------------- |
| Accessed on client or server side | Both server-side & client-side | client-side only | client-side only |
| Lifetime | As configured using Expires option | until deleted | until tab is closed |
| SSL support | Supported | Not supported | Not supported |
| Maximum data size | 4KB | 5 MB | 5MB |
**[⬆ Back to Top](#table-of-contents)**
42. ### What is the main difference between localStorage and sessionStorage
LocalStorage is the same as SessionStorage but it persists the data even when the browser is closed and reopened(i.e it has no expiration time) whereas in sessionStorage data gets cleared when the page session ends.
**[⬆ Back to Top](#table-of-contents)**
43. ### How do you access web storage
The Window object implements the `WindowLocalStorage` and `WindowSessionStorage` objects which has `localStorage`(window.localStorage) and `sessionStorage`(window.sessionStorage) properties respectively. These properties create an instance of the Storage object, through which data items can be set, retrieved and removed for a specific domain and storage type (session or local).
For example, you can read and write on local storage objects as below
```javascript
localStorage.setItem("logo", document.getElementById("logo").value);
localStorage.getItem("logo");
```
**[⬆ Back to Top](#table-of-contents)**
44. ### What are the methods available on session storage
The session storage provided methods for reading, writing and clearing the session data
```javascript
// Save data to sessionStorage
sessionStorage.setItem("key", "value");
// Get saved data from sessionStorage
let data = sessionStorage.getItem("key");
// Remove saved data from sessionStorage
sessionStorage.removeItem("key");
// Remove all saved data from sessionStorage
sessionStorage.clear();
```
**[⬆ Back to Top](#table-of-contents)**
45. ### What is a storage event and its event handler
The StorageEvent is an event that fires when a storage area has been changed in the context of another document. Whereas onstorage property is an EventHandler for processing storage events.
The syntax would be as below
```javascript
window.onstorage = functionRef;
```
Let's take the example usage of onstorage event handler which logs the storage key and it's values
```javascript
window.onstorage = function (e) {
console.log(
"The " +
e.key +
" key has been changed from " +
e.oldValue +
" to " +
e.newValue +
"."
);
};
```
**[⬆ Back to Top](#table-of-contents)**
46. ### Why do you need web storage
Web storage is more secure, and large amounts of data can be stored locally, without affecting website performance. Also, the information is never transferred to the server. Hence this is a more recommended approach than Cookies.
**[⬆ Back to Top](#table-of-contents)**
47. ### How do you check web storage browser support
You need to check browser support for localStorage and sessionStorage before using web storage,
```javascript
if (typeof Storage !== "undefined") {
// Code for localStorage/sessionStorage.
} else {
// Sorry! No Web Storage support..
}
```
**[⬆ Back to Top](#table-of-contents)**
48. ### How do you check web workers browser support
You need to check browser support for web workers before using it
```javascript
if (typeof Worker !== "undefined") {
// code for Web worker support.
} else {
// Sorry! No Web Worker support..
}
```
**[⬆ Back to Top](#table-of-contents)**
49. ### Give an example of a web worker
You need to follow below steps to start using web workers for counting example
1. Create a Web Worker File: You need to write a script to increment the count value. Let's name it as counter.js
```javascript
let i = 0;
function timedCount() {
i = i + 1;
postMessage(i);
setTimeout("timedCount()", 500);
}
timedCount();
```
Here postMessage() method is used to post a message back to the HTML page
1. Create a Web Worker Object: You can create a web worker object by checking for browser support. Let's name this file as web_worker_example.js
```javascript
if (typeof w == "undefined") {
w = new Worker("counter.js");
}
```
and we can receive messages from web worker
```javascript
w.onmessage = function (event) {
document.getElementById("message").innerHTML = event.data;
};
```
1. Terminate a Web Worker:
Web workers will continue to listen for messages (even after the external script is finished) until it is terminated. You can use the terminate() method to terminate listening to the messages.
```javascript
w.terminate();
```
1. Reuse the Web Worker: If you set the worker variable to undefined you can reuse the code
```javascript
w = undefined;
```
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50. ### What are the restrictions of web workers on DOM
WebWorkers don't have access to below javascript objects since they are defined in an external files
1. Window object
2. Document object
3. Parent object
**[⬆ Back to Top](#table-of-contents)**
51. ### What is a promise
A promise is an object that may produce a single value some time in the future with either a resolved value or a reason that it’s not resolved(for example, network error). It will be in one of the 3 possible states: fulfilled, rejected, or pending.
The syntax of Promise creation looks like below,
```javascript
const promise = new Promise(function (resolve, reject) {
// promise description
});
```
The usage of a promise would be as below,
```javascript
const promise = new Promise(
(resolve) => {
setTimeout(() => {
resolve("I'm a Promise!");
}, 5000);
},
(reject) => {}
);
promise.then((value) => console.log(value));
```
The action flow of a promise will be as below,
**[⬆ Back to Top](#table-of-contents)**
52. ### Why do you need a promise
Promises are used to handle asynchronous operations. They provide an alternative approach for callbacks by reducing the callback hell and writing the cleaner code.
**[⬆ Back to Top](#table-of-contents)**
53. ### What are the three states of promise
Promises have three states:
1. **Pending:** This is an initial state of the Promise before an operation begins
2. **Fulfilled:** This state indicates that the specified operation was completed.
3. **Rejected:** This state indicates that the operation did not complete. In this case an error value will be thrown.
**[⬆ Back to Top](#table-of-contents)**
54. ### What is a callback function
A callback function is a function passed into another function as an argument. This function is invoked inside the outer function to complete an action.
Let's take a simple example of how to use callback function
```javascript
function callbackFunction(name) {
console.log("Hello " + name);
}
function outerFunction(callback) {
let name = prompt("Please enter your name.");
callback(name);
}
outerFunction(callbackFunction);
```
**[⬆ Back to Top](#table-of-contents)**
55. ### Why do we need callbacks
The callbacks are needed because javascript is an event driven language. That means instead of waiting for a response javascript will keep executing while listening for other events.
Let's take an example with the first function invoking an API call(simulated by setTimeout) and the next function which logs the message.
```javascript
function firstFunction() {
// Simulate a code delay
setTimeout(function () {
console.log("First function called");
}, 1000);
}
function secondFunction() {
console.log("Second function called");
}
firstFunction();
secondFunction();
Output;
// Second function called
// First function called
```
As observed from the output, javascript didn't wait for the response of the first function and the remaining code block got executed. So callbacks are used in a way to make sure that certain code doesn’t execute until the other code finishes execution.
**[⬆ Back to Top](#table-of-contents)**
56. ### What is a callback hell
Callback Hell is an anti-pattern with multiple nested callbacks which makes code hard to read and debug when dealing with asynchronous logic. The callback hell looks like below,
```javascript
async1(function(){
async2(function(){
async3(function(){
async4(function(){
....
});
});
});
});
```
**[⬆ Back to Top](#table-of-contents)**
57. ### What are server-sent events
Server-sent events (SSE) is a server push technology enabling a browser to receive automatic updates from a server via HTTP connection without resorting to polling. These are a one way communications channel - events flow from server to client only. This has been used in Facebook/Twitter updates, stock price updates, news feeds etc.
**[⬆ Back to Top](#table-of-contents)**
58. ### How do you receive server-sent event notifications
The EventSource object is used to receive server-sent event notifications. For example, you can receive messages from server as below,
```javascript
if (typeof EventSource !== "undefined") {
var source = new EventSource("sse_generator.js");
source.onmessage = function (event) {
document.getElementById("output").innerHTML += event.data + "<br>";
};
}
```
**[⬆ Back to Top](#table-of-contents)**
59. ### How do you check browser support for server-sent events
You can perform browser support for server-sent events before using it as below,
```javascript
if (typeof EventSource !== "undefined") {
// Server-sent events supported. Let's have some code here!
} else {
// No server-sent events supported
}
```
**[⬆ Back to Top](#table-of-contents)**
60. ### What are the events available for server sent events
Below are the list of events available for server sent events
| Event | Description |
|---- | ---------
| onopen | It is used when a connection to the server is opened |
| onmessage | This event is used when a message is received |
| onerror | It happens when an error occurs|
**[⬆ Back to Top](#table-of-contents)**
61. ### What are the main rules of promise
A promise must follow a specific set of rules:
1. A promise is an object that supplies a standard-compliant `.then()` method
2. A pending promise may transition into either fulfilled or rejected state
3. A fulfilled or rejected promise is settled and it must not transition into any other state.
4. Once a promise is settled, the value must not change.
**[⬆ Back to Top](#table-of-contents)**
62. ### What is callback in callback
You can nest one callback inside in another callback to execute the actions sequentially one by one. This is known as callbacks in callbacks.
```javascript
loadScript("/script1.js", function (script) {
console.log("first script is loaded");
loadScript("/script2.js", function (script) {
console.log("second script is loaded");
loadScript("/script3.js", function (script) {
console.log("third script is loaded");
// after all scripts are loaded
});
});
});
```
**[⬆ Back to Top](#table-of-contents)**
63. ### What is promise chaining
The process of executing a sequence of asynchronous tasks one after another using promises is known as Promise chaining. Let's take an example of promise chaining for calculating the final result,
```javascript
new Promise(function (resolve, reject) {
setTimeout(() => resolve(1), 1000);
})
.then(function (result) {
console.log(result); // 1
return result * 2;
})
.then(function (result) {
console.log(result); // 2
return result * 3;
})
.then(function (result) {
console.log(result); // 6
return result * 4;
});
```
In the above handlers, the result is passed to the chain of .then() handlers with the below work flow,
1. The initial promise resolves in 1 second,
2. After that `.then` handler is called by logging the result(1) and then return a promise with the value of result \* 2.
3. After that the value passed to the next `.then` handler by logging the result(2) and return a promise with result \* 3.
4. Finally the value passed to the last `.then` handler by logging the result(6) and return a promise with result \* 4.
**[⬆ Back to Top](#table-of-contents)**
64. ### What is promise.all
Promise.all is a promise that takes an array of promises as an input (an iterable), and it gets resolved when all the promises get resolved or any one of them gets rejected. For example, the syntax of promise.all method is below,
```javascript
Promise.all([Promise1, Promise2, Promise3]) .then(result) => { console.log(result) }) .catch(error => console.log(`Error in promises ${error}`))
```
**Note:** Remember that the order of the promises(output the result) is maintained as per input order.
**[⬆ Back to Top](#table-of-contents)**
65. ### What is the purpose of the race method in promise
Promise.race() method will return the promise instance which is firstly resolved or rejected. Let's take an example of race() method where promise2 is resolved first
```javascript
var promise1 = new Promise(function (resolve, reject) {
setTimeout(resolve, 500, "one");
});
var promise2 = new Promise(function (resolve, reject) {
setTimeout(resolve, 100, "two");
});
Promise.race([promise1, promise2]).then(function (value) {
console.log(value); // "two" // Both promises will resolve, but promise2 is faster
});
```
**[⬆ Back to Top](#table-of-contents)**
66. ### What is a strict mode in javascript
Strict Mode is a new feature in ECMAScript 5 that allows you to place a program, or a function, in a “strict” operating context. This way it prevents certain actions from being taken and throws more exceptions. The literal expression `"use strict";` instructs the browser to use the javascript code in the Strict mode.
**[⬆ Back to Top](#table-of-contents)**
67. ### Why do you need strict mode
Strict mode is useful to write "secure" JavaScript by notifying "bad syntax" into real errors. For example, it eliminates accidentally creating a global variable by throwing an error and also throws an error for assignment to a non-writable property, a getter-only property, a non-existing property, a non-existing variable, or a non-existing object.
**[⬆ Back to Top](#table-of-contents)**
68. ### How do you declare strict mode
The strict mode is declared by adding "use strict"; to the beginning of a script or a function.
If declared at the beginning of a script, it has global scope.
```javascript
"use strict";
x = 3.14; // This will cause an error because x is not declared
```
and if you declare inside a function, it has local scope
```javascript
x = 3.14; // This will not cause an error.
myFunction();
function myFunction() {
"use strict";
y = 3.14; // This will cause an error
}
```
**[⬆ Back to Top](#table-of-contents)**
69. ### What is the purpose of double exclamation
The double exclamation or negation(!!) ensures the resulting type is a boolean. If it was falsey (e.g. 0, null, undefined, etc.), it will be false, otherwise, it will be true.
For example, you can test IE version using this expression as below,
```javascript
let isIE8 = false;
isIE8 = !!navigator.userAgent.match(/MSIE 8.0/);
console.log(isIE8); // returns true or false
```
If you don't use this expression then it returns the original value.
```javascript
console.log(navigator.userAgent.match(/MSIE 8.0/)); // returns either an Array or null
```
**Note:** The expression !! is not an operator, but it is just twice of ! operator.
**[⬆ Back to Top](#table-of-contents)**
70. ### What is the purpose of the delete operator
The delete operator is used to delete the property as well as its value.
```javascript
var user = { firstName: "John", lastName:"Doe", age: 20 };
delete user.age;
console.log(user); // {firstName: "John", lastName:"Doe"}
```
**[⬆ Back to Top](#table-of-contents)**
71. ### What is typeof operator
You can use the JavaScript typeof operator to find the type of a JavaScript variable. It returns the type of a variable or an expression.
```javascript
typeof "John Abraham"; // Returns "string"
typeof (1 + 2); // Returns "number"
typeof [1, 2, 3]; // Returns "object" because all arrays are also objects
```
**[⬆ Back to Top](#table-of-contents)**
72. ### What is undefined property
The undefined property indicates that a variable has not been assigned a value, or declared but not initialized at all. The type of undefined value is undefined too.
```javascript
var user; // Value is undefined, type is undefined
console.log(typeof user); //undefined
```
Any variable can be emptied by setting the value to undefined.
```javascript
user = undefined;
```
**[⬆ Back to Top](#table-of-contents)**
73. ### What is null value
The value null represents the intentional absence of any object value. It is one of JavaScript's primitive values. The type of null value is object.
You can empty the variable by setting the value to null.
```javascript
var user = null;
console.log(typeof user); //object
```
**[⬆ Back to Top](#table-of-contents)**
74. ### What is the difference between null and undefined
Below are the main differences between null and undefined,
| Null | Undefined |
| ----------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------- |
| It is an assignment value which indicates that variable points to no object. | It is not an assignment value where a variable has been declared but has not yet been assigned a value. |
| Type of null is object | Type of undefined is undefined |
| The null value is a primitive value that represents the null, empty, or non-existent reference. | The undefined value is a primitive value used when a variable has not been assigned a value. |
| Indicates the absence of a value for a variable | Indicates absence of variable itself |
| Converted to zero (0) while performing primitive operations | Converted to NaN while performing primitive operations |
**[⬆ Back to Top](#table-of-contents)**
75. ### What is eval
The eval() function evaluates JavaScript code represented as a string. The string can be a JavaScript expression, variable, statement, or sequence of statements.
```javascript
console.log(eval("1 + 2")); // 3
```
**[⬆ Back to Top](#table-of-contents)**
76. ### What is the difference between window and document
Below are the main differences between window and document,
| Window | Document |
| ----------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------- |
| It is the root level element in any web page | It is the direct child of the window object. This is also known as Document Object Model(DOM) |
| By default window object is available implicitly in the page | You can access it via window.document or document. |
| It has methods like alert(), confirm() and properties like document, location | It provides methods like getElementById, getElementsByTagName, createElement etc |
**[⬆ Back to Top](#table-of-contents)**
77. ### How do you access history in javascript
The window.history object contains the browser's history. You can load previous and next URLs in the history using back() and next() methods.
```javascript
function goBack() {
window.history.back();
}
function goForward() {
window.history.forward();
}
```
**Note:** You can also access history without window prefix.
**[⬆ Back to Top](#table-of-contents)**
78. ### How do you detect caps lock key turned on or not
The `mouseEvent getModifierState()` is used to return a boolean value that indicates whether the specified modifier key is activated or not. The modifiers such as CapsLock, ScrollLock and NumLock are activated when they are clicked, and deactivated when they are clicked again.
Let's take an input element to detect the CapsLock on/off behavior with an example,
```html
<input type="password" onmousedown="enterInput(event)" />
<p id="feedback"></p>
<script>
function enterInput(e) {
var flag = e.getModifierState("CapsLock");
if (flag) {
document.getElementById("feedback").innerHTML = "CapsLock activated";
} else {
document.getElementById("feedback").innerHTML =
"CapsLock not activated";
}
}
</script>
```
**[⬆ Back to Top](#table-of-contents)**
79. ### What is isNaN
The isNaN() function is used to determine whether a value is an illegal number (Not-a-Number) or not. i.e, This function returns true if the value equates to NaN. Otherwise it returns false.
```javascript
isNaN("Hello"); //true
isNaN("100"); //false
```
**[⬆ Back to Top](#table-of-contents)**
80. ### What are the differences between undeclared and undefined variables
Below are the major differences between undeclared(not defined) and undefined variables,
| undeclared | undefined |
| ------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
| These variables do not exist in a program and are not declared | These variables declared in the program but have not assigned any value |
| If you try to read the value of an undeclared variable, then a runtime error is encountered | If you try to read the value of an undefined variable, an undefined value is returned. |
**[⬆ Back to Top](#table-of-contents)**
81. ### What are global variables
Global variables are those that are available throughout the length of the code without any scope. The var keyword is used to declare a local variable but if you omit it then it will become global variable
```javascript
msg = "Hello"; // var is missing, it becomes global variable
```
**[⬆ Back to Top](#table-of-contents)**
82. ### What are the problems with global variables
The problem with global variables is the conflict of variable names of local and global scope. It is also difficult to debug and test the code that relies on global variables.
**[⬆ Back to Top](#table-of-contents)**
83. ### What is NaN property
The NaN property is a global property that represents "Not-a-Number" value. i.e, It indicates that a value is not a legal number. It is very rare to use NaN in a program but it can be used as return value for few cases
```javascript
Math.sqrt(-1);
parseInt("Hello");
```
**[⬆ Back to Top](#table-of-contents)**
84. ### What is the purpose of isFinite function
The isFinite() function is used to determine whether a number is a finite, legal number. It returns false if the value is +infinity, -infinity, or NaN (Not-a-Number), otherwise it returns true.
```javascript
isFinite(Infinity); // false
isFinite(NaN); // false
isFinite(-Infinity); // false
isFinite(100); // true
```
**[⬆ Back to Top](#table-of-contents)**
85. ### What is an event flow
Event flow is the order in which event is received on the web page. When you click an element that is nested in various other elements, before your click actually reaches its destination, or target element, it must trigger the click event for each of its parent elements first, starting at the top with the global window object.
There are two ways of event flow
1. Top to Bottom(Event Capturing)
2. Bottom to Top (Event Bubbling)
**[⬆ Back to Top](#table-of-contents)**
86. ### What is event bubbling
Event bubbling is a type of event propagation where the event first triggers on the innermost target element, and then successively triggers on the ancestors (parents) of the target element in the same nesting hierarchy till it reaches the outermost DOM element.
**[⬆ Back to Top](#table-of-contents)**
87. ### What is event capturing
Event capturing is a type of event propagation where the event is first captured by the outermost element, and then successively triggers on the descendants (children) of the target element in the same nesting hierarchy till it reaches the innermost DOM element.
**[⬆ Back to Top](#table-of-contents)**
88. ### How do you submit a form using JavaScript
You can submit a form using `document.forms[0].submit()`. All the form input's information is submitted using onsubmit event handler
```javascript
function submit() {
document.forms[0].submit();
}
```
**[⬆ Back to Top](#table-of-contents)**
89. ### How do you find operating system details
The window.navigator object contains information about the visitor's browser OS details. Some of the OS properties are available under platform property,
```javascript
console.log(navigator.platform);
```
**[⬆ Back to Top](#table-of-contents)**
90. ### What is the difference between document load and DOMContentLoaded events
The `DOMContentLoaded` event is fired when the initial HTML document has been completely loaded and parsed, without waiting for assets(stylesheets, images, and subframes) to finish loading. Whereas The load event is fired when the whole page has loaded, including all dependent resources(stylesheets, images).
**[⬆ Back to Top](#table-of-contents)**
91. ### What is the difference between native, host and user objects
`Native objects` are objects that are part of the JavaScript language defined by the ECMAScript specification. For example, String, Math, RegExp, Object, Function etc core objects defined in the ECMAScript spec.
`Host objects` are objects provided by the browser or runtime environment (Node). For example, window, XmlHttpRequest, DOM nodes etc are considered as host objects.
`User objects` are objects defined in the javascript code. For example, User objects created for profile information.
**[⬆ Back to Top](#table-of-contents)**
92. ### What are the tools or techniques used for debugging JavaScript code
You can use below tools or techniques for debugging javascript
1. Chrome Devtools
2. debugger statement
3. Good old console.log statement
**[⬆ Back to Top](#table-of-contents)**
93. ### What are the pros and cons of promises over callbacks
Below are the list of pros and cons of promises over callbacks,
**Pros:**
1. It avoids callback hell which is unreadable
2. Easy to write sequential asynchronous code with .then()
3. Easy to write parallel asynchronous code with Promise.all()
4. Solves some of the common problems of callbacks(call the callback too late, too early, many times and swallow errors/exceptions)
**Cons:**
1. It makes little complex code
2. You need to load a polyfill if ES6 is not supported
**[⬆ Back to Top](#table-of-contents)**
94. ### What is the difference between an attribute and a property
Attributes are defined on the HTML markup whereas properties are defined on the DOM. For example, the below HTML element has 2 attributes type and value,
```javascript
<input type="text" value="Name:">
```
You can retrieve the attribute value as below,
```javascript
const input = document.querySelector("input");
console.log(input.getAttribute("value")); // Good morning
console.log(input.value); // Good morning
```
And after you change the value of the text field to "Good evening", it becomes like
```javascript
console.log(input.getAttribute("value")); // Good evening
console.log(input.value); // Good evening
```
**[⬆ Back to Top](#table-of-contents)**
95. ### What is same-origin policy
The same-origin policy is a policy that prevents JavaScript from making requests across domain boundaries. An origin is defined as a combination of URI scheme, hostname, and port number. If you enable this policy then it prevents a malicious script on one page from obtaining access to sensitive data on another web page using Document Object Model(DOM).
**[⬆ Back to Top](#table-of-contents)**
96. ### What is the purpose of void 0
Void(0) is used to prevent the page from refreshing. This will be helpful to eliminate the unwanted side-effect, because it will return the undefined primitive value. It is commonly used for HTML documents that use href="JavaScript:Void(0);" within an `<a>` element. i.e, when you click a link, the browser loads a new page or refreshes the same page. But this behavior will be prevented using this expression.
For example, the below link notify the message without reloading the page
```javascript
<a href="JavaScript:void(0);" onclick="alert('Well done!')">
Click Me!
</a>
```
**[⬆ Back to Top](#table-of-contents)**
97. ### Is JavaScript a compiled or interpreted language
JavaScript is an interpreted language, not a compiled language. An interpreter in the browser reads over the JavaScript code, interprets each line, and runs it. Nowadays modern browsers use a technology known as Just-In-Time (JIT) compilation, which compiles JavaScript to executable bytecode just as it is about to run.
**[⬆ Back to Top](#table-of-contents)**
98. ### Is JavaScript a case-sensitive language
Yes, JavaScript is a case sensitive language. The language keywords, variables, function & object names, and any other identifiers must always be typed with a consistent capitalization of letters.
**[⬆ Back to Top](#table-of-contents)**
99. ### Is there any relation between Java and JavaScript
No, they are entirely two different programming languages and have nothing to do with each other. But both of them are Object Oriented Programming languages and like many other languages, they follow similar syntax for basic features(if, else, for, switch, break, continue etc).
**[⬆ Back to Top](#table-of-contents)**
100. ### What are events
Events are "things" that happen to HTML elements. When JavaScript is used in HTML pages, JavaScript can `react` on these events. Some of the examples of HTML events are,
1. Web page has finished loading
2. Input field was changed
3. Button was clicked
Let's describe the behavior of click event for button element,
```javascript
<!doctype html>
<html>
<head>
<script>
function greeting() {
alert('Hello! Good morning');
}
</script>
</head>
<body>
<button type="button" onclick="greeting()">Click me</button>
</body>
</html>
```
**[⬆ Back to Top](#table-of-contents)**
101. ### Who created javascript
JavaScript was created by Brendan Eich in 1995 during his time at Netscape Communications. Initially it was developed under the name `Mocha`, but later the language was officially called `LiveScript` when it first shipped in beta releases of Netscape.
**[⬆ Back to Top](#table-of-contents)**
102. ### What is the use of preventDefault method
The preventDefault() method cancels the event if it is cancelable, meaning that the default action or behaviour that belongs to the event will not occur. For example, prevent form submission when clicking on submit button and prevent opening the page URL when clicking on hyperlink are some common use cases.
```javascript
document
.getElementById("link")
.addEventListener("click", function (event) {
event.preventDefault();
});
```
**Note:** Remember that not all events are cancelable.
**[⬆ Back to Top](#table-of-contents)**
103. ### What is the use of stopPropagation method
The stopPropagation method is used to stop the event from bubbling up the event chain. For example, the below nested divs with stopPropagation method prevents default event propagation when clicking on nested div(Div1)
```javascript
<p>Click DIV1 Element</p>
<div onclick="secondFunc()">DIV 2
<div onclick="firstFunc(event)">DIV 1</div>
</div>
<script>
function firstFunc(event) {
alert("DIV 1");
event.stopPropagation();
}
function secondFunc() {
alert("DIV 2");
}
</script>
```
**[⬆ Back to Top](#table-of-contents)**
104. ### What are the steps involved in return false usage
The return false statement in event handlers performs the below steps,
1. First it stops the browser's default action or behaviour.
2. It prevents the event from propagating the DOM
3. Stops callback execution and returns immediately when called.
**[⬆ Back to Top](#table-of-contents)**
105. ### What is BOM
The Browser Object Model (BOM) allows JavaScript to "talk to" the browser. It consists of the objects navigator, history, screen, location and document which are children of the window. The Browser Object Model is not standardized and can change based on different browsers.
**[⬆ Back to Top](#table-of-contents)**
106. ### What is the use of setTimeout
The setTimeout() method is used to call a function or evaluate an expression after a specified number of milliseconds. For example, let's log a message after 2 seconds using setTimeout method,
```javascript
setTimeout(function () {
console.log("Good morning");
}, 2000);
```
**[⬆ Back to Top](#table-of-contents)**
107. ### What is the use of setInterval
The setInterval() method is used to call a function or evaluate an expression at specified intervals (in milliseconds). For example, let's log a message after 2 seconds using setInterval method,
```javascript
setInterval(function () {
console.log("Good morning");
}, 2000);
```
**[⬆ Back to Top](#table-of-contents)**
108. ### Why is JavaScript treated as Single threaded
JavaScript is a single-threaded language. Because the language specification does not allow the programmer to write code so that the interpreter can run parts of it in parallel in multiple threads or processes. Whereas languages like java, go, C++ can make multi-threaded and multi-process programs.
**[⬆ Back to Top](#table-of-contents)**
109. ### What is an event delegation
Event delegation is a technique for listening to events where you delegate a parent element as the listener for all of the events that happen inside it.
For example, if you wanted to detect field changes in inside a specific form, you can use event delegation technique,
```javascript
var form = document.querySelector("#registration-form");
// Listen for changes to fields inside the form
form.addEventListener(
"input",
function (event) {
// Log the field that was changed
console.log(event.target);
},
false
);
```
**[⬆ Back to Top](#table-of-contents)**
110. ### What is ECMAScript
ECMAScript is the scripting language that forms the basis of JavaScript. ECMAScript standardized by the ECMA International standards organization in the ECMA-262 and ECMA-402 specifications. The first edition of ECMAScript was released in 1997.
**[⬆ Back to Top](#table-of-contents)**
111. ### What is JSON
JSON (JavaScript Object Notation) is a lightweight format that is used for data interchanging. It is based on a subset of JavaScript language in the way objects are built in JavaScript.
**[⬆ Back to Top](#table-of-contents)**
112. ### What are the syntax rules of JSON
Below are the list of syntax rules of JSON
1. The data is in name/value pairs
2. The data is separated by commas
3. Curly braces hold objects
4. Square brackets hold arrays
**[⬆ Back to Top](#table-of-contents)**
113. ### What is the purpose JSON stringify
When sending data to a web server, the data has to be in a string format. You can achieve this by converting JSON object into a string using stringify() method.
```javascript
var userJSON = { name: "John", age: 31 };
var userString = JSON.stringify(userJSON);
console.log(userString); //"{"name":"John","age":31}"
```
**[⬆ Back to Top](#table-of-contents)**
114. ### How do you parse JSON string
When receiving the data from a web server, the data is always in a string format. But you can convert this string value to a javascript object using parse() method.
```javascript
var userString = '{"name":"John","age":31}';
var userJSON = JSON.parse(userString);
console.log(userJSON); // {name: "John", age: 31}
```
**[⬆ Back to Top](#table-of-contents)**
115. ### Why do you need JSON
When exchanging data between a browser and a server, the data can only be text. Since JSON is text only, it can easily be sent to and from a server, and used as a data format by any programming language.
**[⬆ Back to Top](#table-of-contents)**
116. ### What are PWAs
Progressive web applications (PWAs) are a type of mobile app delivered through the web, built using common web technologies including HTML, CSS and JavaScript. These PWAs are deployed to servers, accessible through URLs, and indexed by search engines.
**[⬆ Back to Top](#table-of-contents)**
117. ### What is the purpose of clearTimeout method
The clearTimeout() function is used in javascript to clear the timeout which has been set by setTimeout()function before that. i.e, The return value of setTimeout() function is stored in a variable and it’s passed into the clearTimeout() function to clear the timer.
For example, the below setTimeout method is used to display the message after 3 seconds. This timeout can be cleared by the clearTimeout() method.
```javascript
<script>
var msg;
function greeting() {
alert('Good morning');
}
function start() {
msg =setTimeout(greeting, 3000);
}
function stop() {
clearTimeout(msg);
}
</script>
```
**[⬆ Back to Top](#table-of-contents)**
118. ### What is the purpose of clearInterval method
The clearInterval() function is used in javascript to clear the interval which has been set by setInterval() function. i.e, The return value returned by setInterval() function is stored in a variable and it’s passed into the clearInterval() function to clear the interval.
For example, the below setInterval method is used to display the message for every 3 seconds. This interval can be cleared by the clearInterval() method.
```javascript
<script>
var msg;
function greeting() {
alert('Good morning');
}
function start() {
msg = setInterval(greeting, 3000);
}
function stop() {
clearInterval(msg);
}
</script>
```
**[⬆ Back to Top](#table-of-contents)**
119. ### How do you redirect new page in javascript
In vanilla javascript, you can redirect to a new page using the `location` property of window object. The syntax would be as follows,
```javascript
function redirect() {
window.location.href = "newPage.html";
}
```
**[⬆ Back to Top](#table-of-contents)**
120. ### How do you check whether a string contains a substring
There are 3 possible ways to check whether a string contains a substring or not,
1. **Using includes:** ES6 provided `String.prototype.includes` method to test a string contains a substring
```javascript
var mainString = "hello",
subString = "hell";
mainString.includes(subString);
```
1. **Using indexOf:** In an ES5 or older environment, you can use `String.prototype.indexOf` which returns the index of a substring. If the index value is not equal to -1 then it means the substring exists in the main string.
```javascript
var mainString = "hello",
subString = "hell";
mainString.indexOf(subString) !== -1;
```
1. **Using RegEx:** The advanced solution is using Regular expression's test method(`RegExp.test`), which allows for testing for against regular expressions
```javascript
var mainString = "hello",
regex = /hell/;
regex.test(mainString);
```
**[⬆ Back to Top](#table-of-contents)**
121. ### How do you validate an email in javascript
You can validate an email in javascript using regular expressions. It is recommended to do validations on the server side instead of the client side. Because the javascript can be disabled on the client side.
```javascript
function validateEmail(email) {
var re =
/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
return re.test(String(email).toLowerCase());
}
```
**[⬆ Back to Top](#table-of-contents)**
The above regular expression accepts unicode characters.
122. ### How do you get the current url with javascript
You can use `window.location.href` expression to get the current url path and you can use the same expression for updating the URL too. You can also use `document.URL` for read-only purposes but this solution has issues in FF.
```javascript
console.log("location.href", window.location.href); // Returns full URL
```
**[⬆ Back to Top](#table-of-contents)**
123. ### What are the various url properties of location object
The below `Location` object properties can be used to access URL components of the page,
1. href - The entire URL
2. protocol - The protocol of the URL
3. host - The hostname and port of the URL
4. hostname - The hostname of the URL
5. port - The port number in the URL
6. pathname - The path name of the URL
7. search - The query portion of the URL
8. hash - The anchor portion of the URL
**[⬆ Back to Top](#table-of-contents)**
124. ### How do get query string values in javascript
You can use URLSearchParams to get query string values in javascript. Let's see an example to get the client code value from URL query string,
```javascript
const urlParams = new URLSearchParams(window.location.search);
const clientCode = urlParams.get("clientCode");
```
**[⬆ Back to Top](#table-of-contents)**
125. ### How do you check if a key exists in an object
You can check whether a key exists in an object or not using three approaches,
1. **Using in operator:** You can use the in operator whether a key exists in an object or not
```javascript
"key" in obj;
```
and If you want to check if a key doesn't exist, remember to use parenthesis,
```javascript
!("key" in obj);
```
1. **Using hasOwnProperty method:** You can use `hasOwnProperty` to particularly test for properties of the object instance (and not inherited properties)
```javascript
obj.hasOwnProperty("key"); // true
```
1. **Using undefined comparison:** If you access a non-existing property from an object, the result is undefined. Let’s compare the properties against undefined to determine the existence of the property.
```javascript
const user = {
name: "John",
};
console.log(user.name !== undefined); // true
console.log(user.nickName !== undefined); // false
```
**[⬆ Back to Top](#table-of-contents)**
126. ### How do you loop through or enumerate javascript object
You can use the `for-in` loop to loop through javascript object. You can also make sure that the key you get is an actual property of an object, and doesn't come from the prototype using `hasOwnProperty` method.
```javascript
var object = {
k1: "value1",
k2: "value2",
k3: "value3",
};
for (var key in object) {
if (object.hasOwnProperty(key)) {
console.log(key + " -> " + object[key]); // k1 -> value1 ...
}
}
```
**[⬆ Back to Top](#table-of-contents)**
127. ### How do you test for an empty object
There are different solutions based on ECMAScript versions
1. **Using Object entries(ECMA 7+):** You can use object entries length along with constructor type.
```javascript
Object.entries(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
```
1. **Using Object keys(ECMA 5+):** You can use object keys length along with constructor type.
```javascript
Object.keys(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
```
1. **Using for-in with hasOwnProperty(Pre-ECMA 5):** You can use a for-in loop along with hasOwnProperty.
```javascript
function isEmpty(obj) {
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
return false;
}
}
return JSON.stringify(obj) === JSON.stringify({});
}
```
**[⬆ Back to Top](#table-of-contents)**
128. ### What is an arguments object
The arguments object is an Array-like object accessible inside functions that contains the values of the arguments passed to that function. For example, let's see how to use arguments object inside sum function,
```javascript
function sum() {
var total = 0;
for (var i = 0, len = arguments.length; i < len; ++i) {
total += arguments[i];
}
return total;
}
sum(1, 2, 3); // returns 6
```
**Note:** You can't apply array methods on arguments object. But you can convert into a regular array as below.
```javascript
var argsArray = Array.prototype.slice.call(arguments);
```
**[⬆ Back to Top](#table-of-contents)**
129. ### How do you make first letter of the string in an uppercase
You can create a function which uses a chain of string methods such as charAt, toUpperCase and slice methods to generate a string with the first letter in uppercase.
```javascript
function capitalizeFirstLetter(string) {
return string.charAt(0).toUpperCase() + string.slice(1);
}
```
**[⬆ Back to Top](#table-of-contents)**
130. ### What are the pros and cons of for loop
The for-loop is a commonly used iteration syntax in javascript. It has both pros and cons
#### Pros
1. Works on every environment
2. You can use break and continue flow control statements
#### Cons
1. Too verbose
2. Imperative
3. You might face one-by-off errors
**[⬆ Back to Top](#table-of-contents)**
131. ### How do you display the current date in javascript
You can use `new Date()` to generate a new Date object containing the current date and time. For example, let's display the current date in mm/dd/yyyy
```javascript
var today = new Date();
var dd = String(today.getDate()).padStart(2, "0");
var mm = String(today.getMonth() + 1).padStart(2, "0"); //January is 0!
var yyyy = today.getFullYear();
today = mm + "/" + dd + "/" + yyyy;
document.write(today);
```
**[⬆ Back to Top](#table-of-contents)**
132. ### How do you compare two date objects
You need to use date.getTime() method to compare date values instead of comparison operators (==, !=, ===, and !== operators)
```javascript
var d1 = new Date();
var d2 = new Date(d1);
console.log(d1.getTime() === d2.getTime()); //True
console.log(d1 === d2); // False
```
**[⬆ Back to Top](#table-of-contents)**
133. ### How do you check if a string starts with another string
You can use ECMAScript 6's `String.prototype.startsWith()` method to check if a string starts with another string or not. But it is not yet supported in all browsers. Let's see an example to see this usage,
```javascript
"Good morning".startsWith("Good"); // true
"Good morning".startsWith("morning"); // false
```
**[⬆ Back to Top](#table-of-contents)**
134. ### How do you trim a string in javascript
JavaScript provided a trim method on string types to trim any whitespaces present at the beginning or ending of the string.
```javascript
" Hello World ".trim(); //Hello World
```
If your browser(<IE9) doesn't support this method then you can use below polyfill.
```javascript
if (!String.prototype.trim) {
(function () {
// Make sure we trim BOM and NBSP
var rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g;
String.prototype.trim = function () {
return this.replace(rtrim, "");
};
})();
}
```
**[⬆ Back to Top](#table-of-contents)**
135. ### How do you add a key value pair in javascript
There are two possible solutions to add new properties to an object. Let's take a simple object to explain these solutions.
```javascript
var object = {
key1: value1,
key2: value2,
};
```
1. **Using dot notation:** This solution is useful when you know the name of the property
```javascript
object.key3 = "value3";
```
1. **Using square bracket notation:** This solution is useful when the name of the property is dynamically determined.
```javascript
obj["key3"] = "value3";
```
**[⬆ Back to Top](#table-of-contents)**
136. ### Is the !-- notation represents a special operator
No,that's not a special operator. But it is a combination of 2 standard operators one after the other,
1. A logical not (!)
2. A prefix decrement (--)
At first, the value decremented by one and then tested to see if it is equal to zero or not for determining the truthy/falsy value.
**[⬆ Back to Top](#table-of-contents)**
137. ### How do you assign default values to variables
You can use the logical or operator `||` in an assignment expression to provide a default value. The syntax looks like as below,
```javascript
var a = b || c;
```
As per the above expression, variable 'a 'will get the value of 'c' only if 'b' is falsy (if is null, false, undefined, 0, empty string, or NaN), otherwise 'a' will get the value of 'b'.
**[⬆ Back to Top](#table-of-contents)**
138. ### How do you define multiline strings
You can define multiline string literals using the '\\' character followed by line terminator.
```javascript
var str =
"This is a \
very lengthy \
sentence!";
```
But if you have a space after the '\\' character, the code will look exactly the same, but it will raise a SyntaxError.
**[⬆ Back to Top](#table-of-contents)**
139. ### What is an app shell model
An application shell (or app shell) architecture is one way to build a Progressive Web App that reliably and instantly loads on your users' screens, similar to what you see in native applications. It is useful for getting some initial HTML to the screen fast without a network.
**[⬆ Back to Top](#table-of-contents)**
140. ### Can we define properties for functions
Yes, We can define properties for functions because functions are also objects.
```javascript
fn = function (x) {
//Function code goes here
};
fn.name = "John";
fn.profile = function (y) {
//Profile code goes here
};
```
**[⬆ Back to Top](#table-of-contents)**
141. ### What is the way to find the number of parameters expected by a function
You can use `function.length` syntax to find the number of parameters expected by a function. Let's take an example of `sum` function to calculate the sum of numbers,
```javascript
function sum(num1, num2, num3, num4) {
return num1 + num2 + num3 + num4;
}
sum.length; // 4 is the number of parameters expected.
```
**[⬆ Back to Top](#table-of-contents)**
142. ### What is a polyfill
A polyfill is a piece of JS code used to provide modern functionality on older browsers that do not natively support it. For example, Silverlight plugin polyfill can be used to mimic the functionality of an HTML Canvas element on Microsoft Internet Explorer 7.
**[⬆ Back to Top](#table-of-contents)**
143. ### What are break and continue statements
The break statement is used to "jump out" of a loop. i.e, It breaks the loop and continues executing the code after the loop.
```javascript
for (i = 0; i < 10; i++) {
if (i === 5) {
break;
}
text += "Number: " + i + "<br>";
}
```
The continue statement is used to "jump over" one iteration in the loop. i.e, It breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.
```javascript
for (i = 0; i < 10; i++) {
if (i === 5) {
continue;
}
text += "Number: " + i + "<br>";
}
```
**[⬆ Back to Top](#table-of-contents)**
144. ### What are js labels
The label statement allows us to name loops and blocks in JavaScript. We can then use these labels to refer back to the code later. For example, the below code with labels avoids printing the numbers when they are same,
```javascript
var i, j;
loop1: for (i = 0; i < 3; i++) {
loop2: for (j = 0; j < 3; j++) {
if (i === j) {
continue loop1;
}
console.log("i = " + i + ", j = " + j);
}
}
// Output is:
// "i = 1, j = 0"
// "i = 2, j = 0"
// "i = 2, j = 1"
```
**[⬆ Back to Top](#table-of-contents)**
145. ### What are the benefits of keeping declarations at the top
It is recommended to keep all declarations at the top of each script or function. The benefits of doing this are,
1. Gives cleaner code
2. It provides a single place to look for local variables
3. Easy to avoid unwanted global variables
4. It reduces the possibility of unwanted re-declarations
**[⬆ Back to Top](#table-of-contents)**
146. ### What are the benefits of initializing variables
It is recommended to initialize variables because of the below benefits,
1. It gives cleaner code
2. It provides a single place to initialize variables
3. Avoid undefined values in the code
**[⬆ Back to Top](#table-of-contents)**
147. ### What are the recommendations to create new object
It is recommended to avoid creating new objects using `new Object()`. Instead you can initialize values based on it's type to create the objects.
1. Assign {} instead of new Object()
2. Assign "" instead of new String()
3. Assign 0 instead of new Number()
4. Assign false instead of new Boolean()
5. Assign [] instead of new Array()
6. Assign /()/ instead of new RegExp()
7. Assign function (){} instead of new Function()
You can define them as an example,
```javascript
var v1 = {};
var v2 = "";
var v3 = 0;
var v4 = false;
var v5 = [];
var v6 = /()/;
var v7 = function () {};
```
**[⬆ Back to Top](#table-of-contents)**
148. ### How do you define JSON arrays
JSON arrays are written inside square brackets and arrays contain javascript objects. For example, the JSON array of users would be as below,
```javascript
"users":[
{"firstName":"John", "lastName":"Abrahm"},
{"firstName":"Anna", "lastName":"Smith"},
{"firstName":"Shane", "lastName":"Warn"}
]
```
**[⬆ Back to Top](#table-of-contents)**
149. ### How do you generate random integers
You can use Math.random() with Math.floor() to return random integers. For example, if you want generate random integers between 1 to 10, the multiplication factor should be 10,
```javascript
Math.floor(Math.random() * 10) + 1; // returns a random integer from 1 to 10
Math.floor(Math.random() * 100) + 1; // returns a random integer from 1 to 100
```
**Note:** Math.random() returns a random number between 0 (inclusive), and 1 (exclusive)
**[⬆ Back to Top](#table-of-contents)**
150. ### Can you write a random integers function to print integers with in a range
Yes, you can create a proper random function to return a random number between min and max (both included)
```javascript
function randomInteger(min, max) {
return Math.floor(Math.random() * (max - min + 1)) + min;
}
randomInteger(1, 100); // returns a random integer from 1 to 100
randomInteger(1, 1000); // returns a random integer from 1 to 1000
```
**[⬆ Back to Top](#table-of-contents)**
151. ### What is tree shaking
Tree shaking is a form of dead code elimination. It means that unused modules will not be included in the bundle during the build process and for that it relies on the static structure of ES2015 module syntax,( i.e. import and export). Initially this has been popularized by the ES2015 module bundler `rollup`.
**[⬆ Back to Top](#table-of-contents)**
152. ### What is the need of tree shaking
Tree Shaking can significantly reduce the code size in any application. i.e, The less code we send over the wire the more performant the application will be. For example, if we just want to create a “Hello World” Application using SPA frameworks then it will take around a few MBs, but by tree shaking it can bring down the size to just a few hundred KBs. Tree shaking is implemented in Rollup and Webpack bundlers.
**[⬆ Back to Top](#table-of-contents)**
153. ### Is it recommended to use eval
No, it allows arbitrary code to be run which causes a security problem. As we know that the eval() function is used to run text as code. In most of the cases, it should not be necessary to use it.
**[⬆ Back to Top](#table-of-contents)**
154. ### What is a Regular Expression
A regular expression is a sequence of characters that forms a search pattern. You can use this search pattern for searching data in a text. These can be used to perform all types of text search and text replace operations. Let's see the syntax format now,
```javascript
/pattern/modifiers;
```
For example, the regular expression or search pattern with case-insensitive username would be,
```javascript
/John/i;
```
**[⬆ Back to Top](#table-of-contents)**
155. ### What are the string methods available in Regular expression
Regular Expressions has two string methods: search() and replace().
The search() method uses an expression to search for a match, and returns the position of the match.
```javascript
var msg = "Hello John";
var n = msg.search(/John/i); // 6
```
The replace() method is used to return a modified string where the pattern is replaced.
```javascript
var msg = "Hello John";
var n = msg.replace(/John/i, "Buttler"); // Hello Buttler
```
**[⬆ Back to Top](#table-of-contents)**
156. ### What are modifiers in regular expression
Modifiers can be used to perform case-insensitive and global searches. Let's list down some of the modifiers,
| Modifier | Description |
| -------- | ------------------------------------------------------- |
| i | Perform case-insensitive matching |
| g | Perform a global match rather than stops at first match |
| m | Perform multiline matching |
Let's take an example of global modifier,
```javascript
var text = "Learn JS one by one";
var pattern = /one/g;
var result = text.match(pattern); // one,one
```
**[⬆ Back to Top](#table-of-contents)**
157. ### What are regular expression patterns
Regular Expressions provide a group of patterns in order to match characters. Basically they are categorized into 3 types,
1. **Brackets:** These are used to find a range of characters.
For example, below are some use cases,
1. [abc]: Used to find any of the characters between the brackets(a,b,c)
2. [0-9]: Used to find any of the digits between the brackets
3. (a|b): Used to find any of the alternatives separated with |
2. **Metacharacters:** These are characters with a special meaning
For example, below are some use cases,
1. \\d: Used to find a digit
2. \\s: Used to find a whitespace character
3. \\b: Used to find a match at the beginning or ending of a word
3. **Quantifiers:** These are useful to define quantities
For example, below are some use cases,
1. n+: Used to find matches for any string that contains at least one n
2. n\*: Used to find matches for any string that contains zero or more occurrences of n
3. n?: Used to find matches for any string that contains zero or one occurrences of n
**[⬆ Back to Top](#table-of-contents)**
158. ### What is a RegExp object
RegExp object is a regular expression object with predefined properties and methods. Let's see the simple usage of RegExp object,
```javascript
var regexp = new RegExp("\\w+");
console.log(regexp);
// expected output: /\w+/
```
**[⬆ Back to Top](#table-of-contents)**
159. ### How do you search a string for a pattern
You can use the test() method of regular expression in order to search a string for a pattern, and return true or false depending on the result.
```javascript
var pattern = /you/;
console.log(pattern.test("How are you?")); //true
```
**[⬆ Back to Top](#table-of-contents)**
160. ### What is the purpose of exec method
The purpose of exec method is similar to test method but it executes a search for a match in a specified string and returns a result array, or null instead of returning true/false.
```javascript
var pattern = /you/;
console.log(pattern.exec("How are you?")); //["you", index: 8, input: "How are you?", groups: undefined]
```
**[⬆ Back to Top](#table-of-contents)**
161. ### How do you change the style of a HTML element
You can change inline style or classname of a HTML element using javascript
1. **Using style property:** You can modify inline style using style property
```javascript
document.getElementById("title").style.fontSize = "30px";
```
1. **Using ClassName property:** It is easy to modify element class using className property
```javascript
document.getElementById("title").className = "custom-title";
```
**[⬆ Back to Top](#table-of-contents)**
162. ### What would be the result of 1+2+'3'
The output is going to be `33`. Since `1` and `2` are numeric values, the result of the first two digits is going to be a numeric value `3`. The next digit is a string type value because of that the addition of numeric value `3` and string type value `3` is just going to be a concatenation value `33`.
**[⬆ Back to Top](#table-of-contents)**
163. ### What is a debugger statement
The debugger statement invokes any available debugging functionality, such as setting a breakpoint. If no debugging functionality is available, this statement has no effect.
For example, in the below function a debugger statement has been inserted. So
execution is paused at the debugger statement just like a breakpoint in the script source.
```javascript
function getProfile() {
// code goes here
debugger;
// code goes here
}
```
**[⬆ Back to Top](#table-of-contents)**
164. ### What is the purpose of breakpoints in debugging
You can set breakpoints in the javascript code once the debugger statement is executed and the debugger window pops up. At each breakpoint, javascript will stop executing, and let you examine the JavaScript values. After examining values, you can resume the execution of code using the play button.
**[⬆ Back to Top](#table-of-contents)**
165. ### Can I use reserved words as identifiers
No, you cannot use the reserved words as variables, labels, object or function names. Let's see one simple example,
```javascript
var else = "hello"; // Uncaught SyntaxError: Unexpected token else
```
**[⬆ Back to Top](#table-of-contents)**
166. ### How do you detect a mobile browser
You can use regex which returns a true or false value depending on whether or not the user is browsing with a mobile.
```javascript
window.mobilecheck = function () {
var mobileCheck = false;
(function (a) {
if (
/(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test(
a
) ||
/1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(
a.substr(0, 4)
)
)
mobileCheck = true;
})(navigator.userAgent || navigator.vendor || window.opera);
return mobileCheck;
};
```
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167. ### How do you detect a mobile browser without regexp
You can detect mobile browsers by simply running through a list of devices and checking if the useragent matches anything. This is an alternative solution for RegExp usage,
```javascript
function detectmob() {
if (
navigator.userAgent.match(/Android/i) ||
navigator.userAgent.match(/webOS/i) ||
navigator.userAgent.match(/iPhone/i) ||
navigator.userAgent.match(/iPad/i) ||
navigator.userAgent.match(/iPod/i) ||
navigator.userAgent.match(/BlackBerry/i) ||
navigator.userAgent.match(/Windows Phone/i)
) {
return true;
} else {
return false;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
168. ### How do you get the image width and height using JS
You can programmatically get the image and check the dimensions(width and height) using Javascript.
```javascript
var img = new Image();
img.onload = function () {
console.log(this.width + "x" + this.height);
};
img.src = "http://www.google.com/intl/en_ALL/images/logo.gif";
```
**[⬆ Back to Top](#table-of-contents)**
169. ### How do you make synchronous HTTP request
Browsers provide an XMLHttpRequest object which can be used to make synchronous HTTP requests from JavaScript
```javascript
function httpGet(theUrl) {
var xmlHttpReq = new XMLHttpRequest();
xmlHttpReq.open("GET", theUrl, false); // false for synchronous request
xmlHttpReq.send(null);
return xmlHttpReq.responseText;
}
```
**[⬆ Back to Top](#table-of-contents)**
170. ### How do you make asynchronous HTTP request
Browsers provide an XMLHttpRequest object which can be used to make asynchronous HTTP requests from JavaScript by passing the 3rd parameter as true.
```javascript
function httpGetAsync(theUrl, callback) {
var xmlHttpReq = new XMLHttpRequest();
xmlHttpReq.onreadystatechange = function () {
if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200)
callback(xmlHttpReq.responseText);
};
xmlHttpReq.open("GET", theUrl, true); // true for asynchronous
xmlHttpReq.send(null);
}
```
**[⬆ Back to Top](#table-of-contents)**
171. ### How do you convert date to another timezone in javascript
You can use the toLocaleString() method to convert dates in one timezone to another. For example, let's convert current date to British English timezone as below,
```javascript
console.log(event.toLocaleString("en-GB", { timeZone: "UTC" })); //29/06/2019, 09:56:00
```
**[⬆ Back to Top](#table-of-contents)**
172. ### What are the properties used to get size of window
You can use innerWidth, innerHeight, clientWidth, clientHeight properties of windows, document element and document body objects to find the size of a window. Let's use them combination of these properties to calculate the size of a window or document,
```javascript
var width =
window.innerWidth ||
document.documentElement.clientWidth ||
document.body.clientWidth;
var height =
window.innerHeight ||
document.documentElement.clientHeight ||
document.body.clientHeight;
```
**[⬆ Back to Top](#table-of-contents)**
173. ### What is a conditional operator in javascript
The conditional (ternary) operator is the only JavaScript operator that takes three operands which acts as a shortcut for if statements.
```javascript
var isAuthenticated = false;
console.log(
isAuthenticated ? "Hello, welcome" : "Sorry, you are not authenticated"
); //Sorry, you are not authenticated
```
**[⬆ Back to Top](#table-of-contents)**
174. ### Can you apply chaining on conditional operator
Yes, you can apply chaining on conditional operators similar to if … else if … else if … else chain. The syntax is going to be as below,
```javascript
function traceValue(someParam) {
return condition1
? value1
: condition2
? value2
: condition3
? value3
: value4;
}
// The above conditional operator is equivalent to:
function traceValue(someParam) {
if (condition1) {
return value1;
} else if (condition2) {
return value2;
} else if (condition3) {
return value3;
} else {
return value4;
}
}
```
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175. ### What are the ways to execute javascript after page load
You can execute javascript after page load in many different ways,
1. **window.onload:**
```javascript
window.onload = function ...
```
1. **document.onload:**
```javascript
document.onload = function ...
```
1. **body onload:**
```javascript
<body onload="script();">
```
**[⬆ Back to Top](#table-of-contents)**
176. ### What is the difference between proto and prototype
The `__proto__` object is the actual object that is used in the lookup chain to resolve methods, etc. Whereas `prototype` is the object that is used to build `__proto__` when you create an object with new.
```javascript
new Employee().__proto__ === Employee.prototype;
new Employee().prototype === undefined;
```
There are few more differences,
| feature | Prototype | proto |
| ---------- | ------------------------------------------------------------ | ---------------------------------------------------------- |
| Access | All the function constructors have prototype properties. | All the objects have \_\_proto\_\_ property |
| Purpose | Used to reduce memory wastage with a single copy of function | Used in lookup chain to resolve methods, constructors etc. |
| ECMAScript | Introduced in ES6 | Introduced in ES5 |
| Usage | Frequently used | Rarely used |
**[⬆ Back to Top](#table-of-contents)**
177. ### Give an example where do you really need semicolon
It is recommended to use semicolons after every statement in JavaScript. For example, in the below case it throws an error ".. is not a function" at runtime due to missing semicolon.
```javascript
// define a function
var fn = (function () {
//...
})(
// semicolon missing at this line
// then execute some code inside a closure
function () {
//...
}
)();
```
and it will be interpreted as
```javascript
var fn = (function () {
//...
})(function () {
//...
})();
```
In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a "... is not a function" error at runtime.
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178. ### What is a freeze method
The **freeze()** method is used to freeze an object. Freezing an object does not allow adding new properties to an object,prevents from removing and prevents changing the enumerability, configurability, or writability of existing properties. i.e, It returns the passed object and does not create a frozen copy.
```javascript
const obj = {
prop: 100,
};
Object.freeze(obj);
obj.prop = 200; // Throws an error in strict mode
console.log(obj.prop); //100
```
Remember freezing is only applied to the top-level properties in objects but not for nested objects.
For example, let's try to freeze user object which has employment details as nested object and observe that details have been changed.
```javascript
const user = {
name: "John",
employment: {
department: "IT",
},
};
Object.freeze(user);
user.employment.department = "HR";
```
**Note:** It causes a TypeError if the argument passed is not an object.
**[⬆ Back to Top](#table-of-contents)**
179. ### What is the purpose of freeze method
Below are the main benefits of using freeze method,
1. It is used for freezing objects and arrays.
2. It is used to make an object immutable.
**[⬆ Back to Top](#table-of-contents)**
180. ### Why do I need to use freeze method
In the Object-oriented paradigm, an existing API contains certain elements that are not intended to be extended, modified, or re-used outside of their current context. Hence it works as the `final` keyword which is used in various languages.
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181. ### How do you detect a browser language preference
You can use navigator object to detect a browser language preference as below,
```javascript
var language =
(navigator.languages && navigator.languages[0]) || // Chrome / Firefox
navigator.language || // All browsers
navigator.userLanguage; // IE <= 10
console.log(language);
```
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182. ### How to convert string to title case with javascript
Title case means that the first letter of each word is capitalized. You can convert a string to title case using the below function,
```javascript
function toTitleCase(str) {
return str.replace(/\w\S*/g, function (txt) {
return txt.charAt(0).toUpperCase() + txt.substring(1).toLowerCase();
});
}
toTitleCase("good morning john"); // Good Morning John
```
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183. ### How do you detect javascript disabled in the page
You can use the `<noscript>` tag to detect javascript disabled or not. The code block inside `<noscript>` gets executed when JavaScript is disabled, and is typically used to display alternative content when the page generated in JavaScript.
```javascript
<script type="javascript">
// JS related code goes here
</script>
<noscript>
<a href="next_page.html?noJS=true">JavaScript is disabled in the page. Please click Next Page</a>
</noscript>
```
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184. ### What are various operators supported by javascript
An operator is capable of manipulating(mathematical and logical computations) a certain value or operand. There are various operators supported by JavaScript as below,
1. **Arithmetic Operators:** Includes + (Addition),– (Subtraction), \* (Multiplication), / (Division), % (Modulus), + + (Increment) and – – (Decrement)
2. **Comparison Operators:** Includes = =(Equal),!= (Not Equal), ===(Equal with type), > (Greater than),> = (Greater than or Equal to),< (Less than),<= (Less than or Equal to)
3. **Logical Operators:** Includes &&(Logical AND),||(Logical OR),!(Logical NOT)
4. **Assignment Operators:** Includes = (Assignment Operator), += (Add and Assignment Operator), – = (Subtract and Assignment Operator), \*= (Multiply and Assignment), /= (Divide and Assignment), %= (Modules and Assignment)
5. **Ternary Operators:** It includes conditional(: ?) Operator
6. **typeof Operator:** It uses to find type of variable. The syntax looks like `typeof variable`
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185. ### What is a rest parameter
Rest parameter is an improved way to handle function parameters which allows us to represent an indefinite number of arguments as an array. The syntax would be as below,
```javascript
function f(a, b, ...theArgs) {
// ...
}
```
For example, let's take a sum example to calculate on dynamic number of parameters,
```javascript
function sum(...args) {
let total = 0;
for (const i of args) {
total += i;
}
return total;
}
console.log(sum(1, 2)); //3
console.log(sum(1, 2, 3)); //6
console.log(sum(1, 2, 3, 4)); //13
console.log(sum(1, 2, 3, 4, 5)); //15
```
**Note:** Rest parameter is added in ES2015 or ES6
**[⬆ Back to Top](#table-of-contents)**
186. ### What happens if you do not use rest parameter as a last argument
The rest parameter should be the last argument, as its job is to collect all the remaining arguments into an array. For example, if you define a function like below it doesn’t make any sense and will throw an error.
```javascript
function someFunc(a,…b,c){
//You code goes here
return;
}
```
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187. ### What are the bitwise operators available in javascript
Below are the list of bitwise logical operators used in JavaScript
1. Bitwise AND ( & )
2. Bitwise OR ( | )
3. Bitwise XOR ( ^ )
4. Bitwise NOT ( ~ )
5. Left Shift ( << )
6. Sign Propagating Right Shift ( >> )
7. Zero fill Right Shift ( >>> )
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188. ### What is a spread operator
Spread operator allows iterables( arrays / objects / strings ) to be expanded into single arguments/elements. Let's take an example to see this behavior,
```javascript
function calculateSum(x, y, z) {
return x + y + z;
}
const numbers = [1, 2, 3];
console.log(calculateSum(...numbers)); // 6
```
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189. ### How do you determine whether object is frozen or not
Object.isFrozen() method is used to determine if an object is frozen or not.An object is frozen if all of the below conditions hold true,
1. If it is not extensible.
2. If all of its properties are non-configurable.
3. If all its data properties are non-writable.
The usage is going to be as follows,
```javascript
const object = {
property: "Welcome JS world",
};
Object.freeze(object);
console.log(Object.isFrozen(object));
```
**[⬆ Back to Top](#table-of-contents)**
190. ### How do you determine two values same or not using object
The Object.is() method determines whether two values are the same value. For example, the usage with different types of values would be,
```javascript
Object.is("hello", "hello"); // true
Object.is(window, window); // true
Object.is([], []); // false
```
Two values are the same if one of the following holds:
1. both undefined
2. both null
3. both true or both false
4. both strings of the same length with the same characters in the same order
5. both the same object (means both object have same reference)
6. both numbers and
both +0
both -0
both NaN
both non-zero and both not NaN and both have the same value.
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191. ### What is the purpose of using object is method
Some of the applications of Object's `is` method are follows,
1. It is used for comparison of two strings.
2. It is used for comparison of two numbers.
3. It is used for comparing the polarity of two numbers.
4. It is used for comparison of two objects.
**[⬆ Back to Top](#table-of-contents)**
192. ### How do you copy properties from one object to other
You can use the Object.assign() method which is used to copy the values and properties from one or more source objects to a target object. It returns the target object which has properties and values copied from the source objects. The syntax would be as below,
```javascript
Object.assign(target, ...sources);
```
Let's take example with one source and one target object,
```javascript
const target = { a: 1, b: 2 };
const source = { b: 3, c: 4 };
const returnedTarget = Object.assign(target, source);
console.log(target); // { a: 1, b: 3, c: 4 }
console.log(returnedTarget); // { a: 1, b: 3, c: 4 }
```
As observed in the above code, there is a common property(`b`) from source to target so it's value has been overwritten.
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193. ### What are the applications of assign method
Below are the some of main applications of Object.assign() method,
1. It is used for cloning an object.
2. It is used to merge objects with the same properties.
**[⬆ Back to Top](#table-of-contents)**
194. ### What is a proxy object
The Proxy object is used to define custom behavior for fundamental operations such as property lookup, assignment, enumeration, function invocation, etc. The syntax would be as follows,
```javascript
var p = new Proxy(target, handler);
```
Let's take an example of proxy object,
```javascript
var handler = {
get: function (obj, prop) {
return prop in obj ? obj[prop] : 100;
},
};
var p = new Proxy({}, handler);
p.a = 10;
p.b = null;
console.log(p.a, p.b); // 10, null
console.log("c" in p, p.c); // false, 100
```
In the above code, it uses `get` handler which define the behavior of the proxy when an operation is performed on it
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195. ### What is the purpose of seal method
The **Object.seal()** method is used to seal an object, by preventing new properties from being added to it and marking all existing properties as non-configurable. But values of present properties can still be changed as long as they are writable. Let's see the below example to understand more about seal() method
```javascript
const object = {
property: "Welcome JS world",
};
Object.seal(object);
object.property = "Welcome to object world";
console.log(Object.isSealed(object)); // true
delete object.property; // You cannot delete when sealed
console.log(object.property); //Welcome to object world
```
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196. ### What are the applications of seal method
Below are the main applications of Object.seal() method,
1. It is used for sealing objects and arrays.
2. It is used to make an object immutable.
**[⬆ Back to Top](#table-of-contents)**
197. ### What are the differences between freeze and seal methods
If an object is frozen using the Object.freeze() method then its properties become immutable and no changes can be made in them whereas if an object is sealed using the Object.seal() method then the changes can be made in the existing properties of the object.
**[⬆ Back to Top](#table-of-contents)**
198. ### How do you determine if an object is sealed or not
The Object.isSealed() method is used to determine if an object is sealed or not. An object is sealed if all of the below conditions hold true
1. If it is not extensible.
2. If all of its properties are non-configurable.
3. If it is not removable (but not necessarily non-writable).
Let's see it in the action
```javascript
const object = {
property: "Hello, Good morning",
};
Object.seal(object); // Using seal() method to seal the object
console.log(Object.isSealed(object)); // checking whether the object is sealed or not
```
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199. ### How do you get enumerable key and value pairs
The Object.entries() method is used to return an array of a given object's own enumerable string-keyed property [key, value] pairs, in the same order as that provided by a for...in loop. Let's see the functionality of object.entries() method in an example,
```javascript
const object = {
a: "Good morning",
b: 100,
};
for (let [key, value] of Object.entries(object)) {
console.log(`${key}: ${value}`); // a: 'Good morning'
// b: 100
}
```
**Note:** The order is not guaranteed as object defined.
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200. ### What is the main difference between Object.values and Object.entries method
The Object.values() method's behavior is similar to Object.entries() method but it returns an array of values instead [key,value] pairs.
```javascript
const object = {
a: "Good morning",
b: 100,
};
for (let value of Object.values(object)) {
console.log(`${value}`); // 'Good morning'
100;
}
```
**[⬆ Back to Top](#table-of-contents)**
201. ### How can you get the list of keys of any object
You can use the `Object.keys()` method which is used to return an array of a given object's own property names, in the same order as we get with a normal loop. For example, you can get the keys of a user object,
```javascript
const user = {
name: "John",
gender: "male",
age: 40,
};
console.log(Object.keys(user)); //['name', 'gender', 'age']
```
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202. ### How do you create an object with prototype
The Object.create() method is used to create a new object with the specified prototype object and properties. i.e, It uses an existing object as the prototype of the newly created object. It returns a new object with the specified prototype object and properties.
```javascript
const user = {
name: "John",
printInfo: function () {
console.log(`My name is ${this.name}.`);
},
};
const admin = Object.create(user);
admin.name = "Nick"; // Remember that "name" is a property set on "admin" but not on "user" object
admin.printInfo(); // My name is Nick
```
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203. ### What is a WeakSet
WeakSet is used to store a collection of weakly(weak references) held objects. The syntax would be as follows,
```javascript
new WeakSet([iterable]);
```
Let's see the below example to explain it's behavior,
```javascript
var ws = new WeakSet();
var user = {};
ws.add(user);
ws.has(user); // true
ws.delete(user); // removes user from the set
ws.has(user); // false, user has been removed
```
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204. ### What are the differences between WeakSet and Set
The main difference is that references to objects in Set are strong while references to objects in WeakSet are weak. i.e, An object in WeakSet can be garbage collected if there is no other reference to it.
Other differences are,
1. Sets can store any value Whereas WeakSets can store only collections of objects
2. WeakSet does not have size property unlike Set
3. WeakSet does not have methods such as clear, keys, values, entries, forEach.
4. WeakSet is not iterable.
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205. ### List down the collection of methods available on WeakSet
Below are the list of methods available on WeakSet,
1. add(value): A new object is appended with the given value to the weakset
2. delete(value): Deletes the value from the WeakSet collection.
3. has(value): It returns true if the value is present in the WeakSet Collection, otherwise it returns false.
Let's see the functionality of all the above methods in an example,
```javascript
var weakSetObject = new WeakSet();
var firstObject = {};
var secondObject = {};
// add(value)
weakSetObject.add(firstObject);
weakSetObject.add(secondObject);
console.log(weakSetObject.has(firstObject)); //true
weakSetObject.delete(secondObject);
```
**[⬆ Back to Top](#table-of-contents)**
206. ### What is a WeakMap
The WeakMap object is a collection of key/value pairs in which the keys are weakly referenced. In this case, keys must be objects and the values can be arbitrary values. The syntax is looking like as below,
```javascript
new WeakMap([iterable]);
```
Let's see the below example to explain it's behavior,
```javascript
var ws = new WeakMap();
var user = {};
ws.set(user);
ws.has(user); // true
ws.delete(user); // removes user from the map
ws.has(user); // false, user has been removed
```
**[⬆ Back to Top](#table-of-contents)**
207. ### What are the differences between WeakMap and Map
The main difference is that references to key objects in Map are strong while references to key objects in WeakMap are weak. i.e, A key object in WeakMap can be garbage collected if there is no other reference to it.
Other differences are,
1. Maps can store any key type Whereas WeakMaps can store only collections of key objects
2. WeakMap does not have size property unlike Map
3. WeakMap does not have methods such as clear, keys, values, entries, forEach.
4. WeakMap is not iterable.
**[⬆ Back to Top](#table-of-contents)**
208. ### List down the collection of methods available on WeakMap
Below are the list of methods available on WeakMap,
1. set(key, value): Sets the value for the key in the WeakMap object. Returns the WeakMap object.
2. delete(key): Removes any value associated to the key.
3. has(key): Returns a Boolean asserting whether a value has been associated to the key in the WeakMap object or not.
4. get(key): Returns the value associated to the key, or undefined if there is none.
Let's see the functionality of all the above methods in an example,
```javascript
var weakMapObject = new WeakMap();
var firstObject = {};
var secondObject = {};
// set(key, value)
weakMapObject.set(firstObject, "John");
weakMapObject.set(secondObject, 100);
console.log(weakMapObject.has(firstObject)); //true
console.log(weakMapObject.get(firstObject)); // John
weakMapObject.delete(secondObject);
```
**[⬆ Back to Top](#table-of-contents)**
209. ### What is the purpose of uneval
The uneval() is an inbuilt function which is used to create a string representation of the source code of an Object. It is a top-level function and is not associated with any object. Let's see the below example to know more about it's functionality,
```javascript
var a = 1;
uneval(a); // returns a String containing 1
uneval(function user() {}); // returns "(function user(){})"
```
The `uneval()` function has been deprecated. It is recommended to use `toString()` for functions and `JSON.toStringify()` for other cases.
```javascript
function user() {}
console.log(user.toString()); // returns "(function user(){})"
```
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210. ### How do you encode an URL
The encodeURI() function is used to encode complete URI which has special characters except (, / ? : @ & = + $ #) characters.
```javascript
var uri = "https://mozilla.org/?x=шеллы";
var encoded = encodeURI(uri);
console.log(encoded); // https://mozilla.org/?x=%D1%88%D0%B5%D0%BB%D0%BB%D1%8B
```
**[⬆ Back to Top](#table-of-contents)**
211. ### How do you decode an URL
The decodeURI() function is used to decode a Uniform Resource Identifier (URI) previously created by encodeURI().
```javascript
var uri = "https://mozilla.org/?x=шеллы";
var encoded = encodeURI(uri);
console.log(encoded); // https://mozilla.org/?x=%D1%88%D0%B5%D0%BB%D0%BB%D1%8B
try {
console.log(decodeURI(encoded)); // "https://mozilla.org/?x=шеллы"
} catch (e) {
// catches a malformed URI
console.error(e);
}
```
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212. ### How do you print the contents of web page
The window object provided a print() method which is used to print the contents of the current window. It opens a Print dialog box which lets you choose between various printing options. Let's see the usage of print method in an example,
```html
<input type="button" value="Print" onclick="window.print()" />
```
**Note:** In most browsers, it will block while the print dialog is open.
**[⬆ Back to Top](#table-of-contents)**
213. ### What is the difference between uneval and eval
The `uneval` function returns the source of a given object; whereas the `eval` function does the opposite, by evaluating that source code in a different memory area. Let's see an example to clarify the difference,
```javascript
var msg = uneval(function greeting() {
return "Hello, Good morning";
});
var greeting = eval(msg);
greeting(); // returns "Hello, Good morning"
```
**[⬆ Back to Top](#table-of-contents)**
214. ### What is an anonymous function
An anonymous function is a function without a name! Anonymous functions are commonly assigned to a variable name or used as a callback function. The syntax would be as below,
```javascript
function (optionalParameters) {
//do something
}
const myFunction = function(){ //Anonymous function assigned to a variable
//do something
};
[1, 2, 3].map(function(element){ //Anonymous function used as a callback function
//do something
});
```
Let's see the above anonymous function in an example,
```javascript
var x = function (a, b) {
return a * b;
};
var z = x(5, 10);
console.log(z); // 50
```
**[⬆ Back to Top](#table-of-contents)**
215. ### What is the precedence order between local and global variables
A local variable takes precedence over a global variable with the same name. Let's see this behavior in an example.
```javascript
var msg = "Good morning";
function greeting() {
msg = "Good Evening";
console.log(msg); // Good Evening
}
greeting();
```
**[⬆ Back to Top](#table-of-contents)**
216. ### What are javascript accessors
ECMAScript 5 introduced javascript object accessors or computed properties through getters and setters. Getters uses the `get` keyword whereas Setters uses the `set` keyword.
```javascript
var user = {
firstName: "John",
lastName: "Abraham",
language: "en",
get lang() {
return this.language;
},
set lang(lang) {
this.language = lang;
},
};
console.log(user.lang); // getter access lang as en
user.lang = "fr";
console.log(user.lang); // setter used to set lang as fr
```
**[⬆ Back to Top](#table-of-contents)**
217. ### How do you define property on Object constructor
The Object.defineProperty() static method is used to define a new property directly on an object, or modify an existing property on an object, and returns the object. Let's see an example to know how to define property,
```javascript
const newObject = {};
Object.defineProperty(newObject, "newProperty", {
value: 100,
writable: false,
});
console.log(newObject.newProperty); // 100
newObject.newProperty = 200; // It throws an error in strict mode due to writable setting
```
**[⬆ Back to Top](#table-of-contents)**
218. ### What is the difference between get and defineProperty
Both have similar results until unless you use classes. If you use `get` the property will be defined on the prototype of the object whereas using `Object.defineProperty()` the property will be defined on the instance it is applied to.
**[⬆ Back to Top](#table-of-contents)**
219. ### What are the advantages of Getters and Setters
Below are the list of benefits of Getters and Setters,
1. They provide simpler syntax
2. They are used for defining computed properties, or accessors in JS.
3. Useful to provide equivalence relation between properties and methods
4. They can provide better data quality
5. Useful for doing things behind the scenes with the encapsulated logic.
**[⬆ Back to Top](#table-of-contents)**
220. ### Can I add getters and setters using defineProperty method
Yes, You can use the `Object.defineProperty()` method to add Getters and Setters. For example, the below counter object uses increment, decrement, add and subtract properties,
```javascript
var obj = { counter: 0 };
// Define getters
Object.defineProperty(obj, "increment", {
get: function () {
this.counter++;
},
});
Object.defineProperty(obj, "decrement", {
get: function () {
this.counter--;
},
});
// Define setters
Object.defineProperty(obj, "add", {
set: function (value) {
this.counter += value;
},
});
Object.defineProperty(obj, "subtract", {
set: function (value) {
this.counter -= value;
},
});
obj.add = 10;
obj.subtract = 5;
console.log(obj.increment); //6
console.log(obj.decrement); //5
```
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221. ### What is the purpose of switch-case
The switch case statement in JavaScript is used for decision making purposes. In a few cases, using the switch case statement is going to be more convenient than if-else statements. The syntax would be as below,
```javascript
switch (expression)
{
case value1:
statement1;
break;
case value2:
statement2;
break;
.
.
case valueN:
statementN;
break;
default:
statementDefault;
}
```
The above multi-way branch statement provides an easy way to dispatch execution to different parts of code based on the value of the expression.
**[⬆ Back to Top](#table-of-contents)**
222. ### What are the conventions to be followed for the usage of switch case
Below are the list of conventions should be taken care,
1. The expression can be of type either number or string.
2. Duplicate values are not allowed for the expression.
3. The default statement is optional. If the expression passed to switch does not match with any case value then the statement within default case will be executed.
4. The break statement is used inside the switch to terminate a statement sequence.
5. The break statement is optional. But if it is omitted, the execution will continue on into the next case.
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223. ### What are primitive data types
A primitive data type is data that has a primitive value (which has no properties or methods). There are 7 types of primitive data types.
1. string
2. number
3. boolean
4. null
5. undefined
6. bigint
7. symbol
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224. ### What are the different ways to access object properties
There are 3 possible ways for accessing the property of an object.
1. **Dot notation:** It uses dot for accessing the properties
```javascript
objectName.property;
```
1. **Square brackets notation:** It uses square brackets for property access
```javascript
objectName["property"];
```
1. **Expression notation:** It uses expression in the square brackets
```javascript
objectName[expression];
```
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225. ### What are the function parameter rules
JavaScript functions follow below rules for parameters,
1. The function definitions do not specify data types for parameters.
2. Do not perform type checking on the passed arguments.
3. Do not check the number of arguments received.
i.e, The below function follows the above rules,
```javascript
function functionName(parameter1, parameter2, parameter3) {
console.log(parameter1); // 1
}
functionName(1);
```
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226. ### What is an error object
An error object is a built in error object that provides error information when an error occurs. It has two properties: name and message. For example, the below function logs error details,
```javascript
try {
greeting("Welcome");
} catch (err) {
console.log(err.name + "<br>" + err.message);
}
```
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227. ### When you get a syntax error
A SyntaxError is thrown if you try to evaluate code with a syntax error. For example, the below missing quote for the function parameter throws a syntax error
```javascript
try {
eval("greeting('welcome)"); // Missing ' will produce an error
} catch (err) {
console.log(err.name);
}
```
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228. ### What are the different error names from error object
There are 6 different types of error names returned from error object,
| Error Name | Description |
|---- | ---------
| EvalError | An error has occurred in the eval() function |
| RangeError | An error has occurred with a number "out of range" |
| ReferenceError | An error due to an illegal reference|
| SyntaxError | An error due to a syntax error|
| TypeError | An error due to a type error |
| URIError | An error due to encodeURI() |
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229. ### What are the various statements in error handling
Below are the list of statements used in an error handling,
1. **try:** This statement is used to test a block of code for errors
2. **catch:** This statement is used to handle the error
3. **throw:** This statement is used to create custom errors.
4. **finally:** This statement is used to execute code after try and catch regardless of the result.
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230. ### What are the two types of loops in javascript
1. **Entry Controlled loops:** In this kind of loop type, the test condition is tested before entering the loop body. For example, For Loop and While Loop comes under this category.
2. **Exit Controlled Loops:** In this kind of loop type, the test condition is tested or evaluated at the end of the loop body. i.e, the loop body will execute at least once irrespective of test condition true or false. For example, do-while loop comes under this category.
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231. ### What is nodejs
Node.js is a server-side platform built on Chrome's JavaScript runtime for easily building fast and scalable network applications. It is an event-based, non-blocking, asynchronous I/O runtime that uses Google's V8 JavaScript engine and libuv library.
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232. ### What is an Intl object
The Intl object is the namespace for the ECMAScript Internationalization API, which provides language sensitive string comparison, number formatting, and date and time formatting. It provides access to several constructors and language sensitive functions.
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233. ### How do you perform language specific date and time formatting
You can use the `Intl.DateTimeFormat` object which is a constructor for objects that enable language-sensitive date and time formatting. Let's see this behavior with an example,
```javascript
var date = new Date(Date.UTC(2019, 07, 07, 3, 0, 0));
console.log(new Intl.DateTimeFormat("en-GB").format(date)); // 07/08/2019
console.log(new Intl.DateTimeFormat("en-AU").format(date)); // 07/08/2019
```
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234. ### What is an Iterator
An iterator is an object which defines a sequence and a return value upon its termination. It implements the Iterator protocol with a `next()` method which returns an object with two properties: `value` (the next value in the sequence) and `done` (which is true if the last value in the sequence has been consumed).
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235. ### How does synchronous iteration works
Synchronous iteration was introduced in ES6 and it works with below set of components,
**Iterable:** It is an object which can be iterated over via a method whose key is Symbol.iterator.
**Iterator:** It is an object returned by invoking `[Symbol.iterator]()` on an iterable. This iterator object wraps each iterated element in an object and returns it via `next()` method one by one.
**IteratorResult:** It is an object returned by `next()` method. The object contains two properties; the `value` property contains an iterated element and the `done` property determines whether the element is the last element or not.
Let's demonstrate synchronous iteration with an array as below,
```javascript
const iterable = ["one", "two", "three"];
const iterator = iterable[Symbol.iterator]();
console.log(iterator.next()); // { value: 'one', done: false }
console.log(iterator.next()); // { value: 'two', done: false }
console.log(iterator.next()); // { value: 'three', done: false }
console.log(iterator.next()); // { value: 'undefined, done: true }
```
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236. ### What is an event loop
The event loop is a process that continuously monitors both the call stack and the event queue and checks whether or not the call stack is empty. If the call stack is empty and there are pending events in the event queue, the event loop dequeues the event from the event queue and pushes it to the call stack. The call stack executes the event, and any additional events generated during the execution are added to the end of the event queue.
**Note:** The event loop allows Node.js to perform non-blocking I/O operations, even though JavaScript is single-threaded, by offloading operations to the system kernel whenever possible. Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background.
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237. ### What is call stack
Call Stack is a data structure for javascript interpreters to keep track of function calls(creates execution context) in the program. It has two major actions,
1. Whenever you call a function for its execution, you are pushing it to the stack.
2. Whenever the execution is completed, the function is popped out of the stack.
Let's take an example and it's state representation in a diagram format
```javascript
function hungry() {
eatFruits();
}
function eatFruits() {
return "I'm eating fruits";
}
// Invoke the `hungry` function
hungry();
```
The above code processed in a call stack as below,
1. Add the `hungry()` function to the call stack list and execute the code.
2. Add the `eatFruits()` function to the call stack list and execute the code.
3. Delete the `eatFruits()` function from our call stack list.
4. Delete the `hungry()` function from the call stack list since there are no items anymore.
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238. ### What is an event queue
The event queue follows the queue data structure. It stores async callbacks to be added to the call stack. It is also known as the Callback Queue or Macrotask Queue.
Whenever the call stack receives an async function, it is moved into the Web API. Based on the function, Web API executes it and awaits the result. Once it is finished, it moves the callback into the event queue (the callback of the promise is moved into the microtask queue).
The event loop constantly checks whether or not the call stack is empty. Once the call stack is empty and there is a callback in the event queue, the event loop moves the callback into the call stack. But if there is a callback in the microtask queue as well, it is moved first. The microtask queue has a higher priority than the event queue.
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239. ### What is a decorator
A decorator is an expression that evaluates to a function and that takes the target, name, and decorator descriptor as arguments. Also, it optionally returns a decorator descriptor to install on the target object. Let's define admin decorator for user class at design time,
```javascript
function admin(isAdmin) {
return function(target) {
target.isAdmin = isAdmin;
}
}
@admin(true)
class User() {
}
console.log(User.isAdmin); //true
@admin(false)
class User() {
}
console.log(User.isAdmin); //false
```
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240. ### What are the properties of Intl object
Below are the list of properties available on Intl object,
1. **Collator:** These are the objects that enable language-sensitive string comparison.
2. **DateTimeFormat:** These are the objects that enable language-sensitive date and time formatting.
3. **ListFormat:** These are the objects that enable language-sensitive list formatting.
4. **NumberFormat:** Objects that enable language-sensitive number formatting.
5. **PluralRules:** Objects that enable plural-sensitive formatting and language-specific rules for plurals.
6. **RelativeTimeFormat:** Objects that enable language-sensitive relative time formatting.
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241. ### What is an Unary operator
The unary(+) operator is used to convert a variable to a number.If the variable cannot be converted, it will still become a number but with the value NaN. Let's see this behavior in an action.
```javascript
var x = "100";
var y = +x;
console.log(typeof x, typeof y); // string, number
var a = "Hello";
var b = +a;
console.log(typeof a, typeof b, b); // string, number, NaN
```
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242. ### How do you sort elements in an array
The sort() method is used to sort the elements of an array in place and returns the sorted array. The example usage would be as below,
```javascript
var months = ["Aug", "Sep", "Jan", "June"];
months.sort();
console.log(months); // ["Aug", "Jan", "June", "Sep"]
```
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243. ### What is the purpose of compareFunction while sorting arrays
The compareFunction is used to define the sort order. If omitted, the array elements are converted to strings, then sorted according to each character's Unicode code point value. Let's take an example to see the usage of compareFunction,
```javascript
let numbers = [1, 2, 5, 3, 4];
numbers.sort((a, b) => b - a);
console.log(numbers); // [5, 4, 3, 2, 1]
```
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244. ### How do you reversing an array
You can use the reverse() method to reverse the elements in an array. This method is useful to sort an array in descending order. Let's see the usage of reverse() method in an example,
```javascript
let numbers = [1, 2, 5, 3, 4];
numbers.sort((a, b) => b - a);
numbers.reverse();
console.log(numbers); // [1, 2, 3, 4 ,5]
```
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245. ### How do you find min and max value in an array
You can use `Math.min` and `Math.max` methods on array variables to find the minimum and maximum elements within an array. Let's create two functions to find the min and max value with in an array,
```javascript
var marks = [50, 20, 70, 60, 45, 30];
function findMin(arr) {
return Math.min.apply(null, arr);
}
function findMax(arr) {
return Math.max.apply(null, arr);
}
console.log(findMin(marks));
console.log(findMax(marks));
```
**[⬆ Back to Top](#table-of-contents)**
246. ### How do you find min and max values without Math functions
You can write functions which loop through an array comparing each value with the lowest value or highest value to find the min and max values. Let's create those functions to find min and max values,
```javascript
var marks = [50, 20, 70, 60, 45, 30];
function findMin(arr) {
var length = arr.length;
var min = Infinity;
while (length--) {
if (arr[length] < min) {
min = arr[length];
}
}
return min;
}
function findMax(arr) {
var length = arr.length;
var max = -Infinity;
while (length--) {
if (arr[length] > max) {
max = arr[length];
}
}
return max;
}
console.log(findMin(marks));
console.log(findMax(marks));
```
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247. ### What is an empty statement and purpose of it
The empty statement is a semicolon (;) indicating that no statement will be executed, even if JavaScript syntax requires one. Since there is no action with an empty statement you might think that it's usage is quite less, but the empty statement is occasionally useful when you want to create a loop that has an empty body. For example, you can initialize an array with zero values as below,
```javascript
// Initialize an array a
for (let i = 0; i < a.length; a[i++] = 0);
```
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248. ### How do you get metadata of a module
You can use the `import.meta` object which is a meta-property exposing context-specific meta data to a JavaScript module. It contains information about the current module, such as the module's URL. In browsers, you might get different meta data than NodeJS.
```javascript
<script type="module" src="welcome-module.js"></script>;
console.log(import.meta); // { url: "file:///home/user/welcome-module.js" }
```
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249. ### What is a comma operator
The comma operator is used to evaluate each of its operands from left to right and returns the value of the last operand. This is totally different from comma usage within arrays, objects, and function arguments and parameters. For example, the usage for numeric expressions would be as below,
```javascript
var x = 1;
x = (x++, x);
console.log(x); // 2
```
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250. ### What is the advantage of a comma operator
It is normally used to include multiple expressions in a location that requires a single expression. One of the common usages of this comma operator is to supply multiple parameters in a `for` loop. For example, the below for loop uses multiple expressions in a single location using comma operator,
```javascript
for (var a = 0, b =10; a <= 10; a++, b--)
```
You can also use the comma operator in a return statement where it processes before returning.
```javascript
function myFunction() {
var a = 1;
return (a += 10), a; // 11
}
```
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251. ### What is typescript
TypeScript is a typed superset of JavaScript created by Microsoft that adds optional types, classes, async/await, and many other features, and compiles to plain JavaScript. Angular built entirely in TypeScript and used as a primary language. You can install it globally as
```bash
npm install -g typescript
```
Let's see a simple example of TypeScript usage,
```typescript
function greeting(name: string): string {
return "Hello, " + name;
}
let user = "Sudheer";
console.log(greeting(user));
```
The greeting method allows only string type as argument.
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252. ### What are the differences between javascript and typescript
Below are the list of differences between javascript and typescript,
| feature | typescript | javascript |
| ------------------- | ------------------------------------- | ----------------------------------------------- |
| Language paradigm | Object oriented programming language | Scripting language |
| Typing support | Supports static typing | It has dynamic typing |
| Modules | Supported | Not supported |
| Interface | It has interfaces concept | Doesn't support interfaces |
| Optional parameters | Functions support optional parameters | No support of optional parameters for functions |
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253. ### What are the advantages of typescript over javascript
Below are some of the advantages of typescript over javascript,
1. TypeScript is able to find compile time errors at the development time only and it makes sures less runtime errors. Whereas javascript is an interpreted language.
2. TypeScript is strongly-typed or supports static typing which allows for checking type correctness at compile time. This is not available in javascript.
3. TypeScript compiler can compile the .ts files into ES3,ES4 and ES5 unlike ES6 features of javascript which may not be supported in some browsers.
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254. ### What is an object initializer
An object initializer is an expression that describes the initialization of an Object. The syntax for this expression is represented as a comma-delimited list of zero or more pairs of property names and associated values of an object, enclosed in curly braces ({}). This is also known as literal notation. It is one of the ways to create an object.
```javascript
var initObject = { a: "John", b: 50, c: {} };
console.log(initObject.a); // John
```
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255. ### What is a constructor method
The constructor method is a special method for creating and initializing an object created within a class. If you do not specify a constructor method, a default constructor is used. The example usage of constructor would be as below,
```javascript
class Employee {
constructor() {
this.name = "John";
}
}
var employeeObject = new Employee();
console.log(employeeObject.name); // John
```
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256. ### What happens if you write constructor more than once in a class
The "constructor" in a class is a special method and it should be defined only once in a class. i.e, If you write a constructor method more than once in a class it will throw a `SyntaxError` error.
```javascript
class Employee {
constructor() {
this.name = "John";
}
constructor() { // Uncaught SyntaxError: A class may only have one constructor
this.age = 30;
}
}
var employeeObject = new Employee();
console.log(employeeObject.name);
```
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257. ### How do you call the constructor of a parent class
You can use the `super` keyword to call the constructor of a parent class. Remember that `super()` must be called before using 'this' reference. Otherwise it will cause a reference error. Let's the usage of it,
```javascript
class Square extends Rectangle {
constructor(length) {
super(length, length);
this.name = "Square";
}
get area() {
return this.width * this.height;
}
set area(value) {
this.area = value;
}
}
```
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258. ### How do you get the prototype of an object
You can use the `Object.getPrototypeOf(obj)` method to return the prototype of the specified object. i.e. The value of the internal `prototype` property. If there are no inherited properties then `null` value is returned.
```javascript
const newPrototype = {};
const newObject = Object.create(newPrototype);
console.log(Object.getPrototypeOf(newObject) === newPrototype); // true
```
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259. ### What happens If I pass string type for getPrototype method
In ES5, it will throw a TypeError exception if the obj parameter isn't an object. Whereas in ES2015, the parameter will be coerced to an `Object`.
```javascript
// ES5
Object.getPrototypeOf("James"); // TypeError: "James" is not an object
// ES2015
Object.getPrototypeOf("James"); // String.prototype
```
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260. ### How do you set prototype of one object to another
You can use the `Object.setPrototypeOf()` method that sets the prototype (i.e., the internal `Prototype` property) of a specified object to another object or null. For example, if you want to set prototype of a square object to rectangle object would be as follows,
```javascript
Object.setPrototypeOf(Square.prototype, Rectangle.prototype);
Object.setPrototypeOf({}, null);
```
**[⬆ Back to Top](#table-of-contents)**
261. ### How do you check whether an object can be extendable or not
The `Object.isExtensible()` method is used to determine if an object is extendable or not. i.e, Whether it can have new properties added to it or not.
```javascript
const newObject = {};
console.log(Object.isExtensible(newObject)); //true
```
**Note:** By default, all the objects are extendable. i.e, The new properties can be added or modified.
**[⬆ Back to Top](#table-of-contents)**
262. ### How do you prevent an object to extend
The `Object.preventExtensions()` method is used to prevent new properties from ever being added to an object. In other words, it prevents future extensions to the object. Let's see the usage of this property,
```javascript
const newObject = {};
Object.preventExtensions(newObject); // NOT extendable
try {
Object.defineProperty(newObject, "newProperty", {
// Adding new property
value: 100,
});
} catch (e) {
console.log(e); // TypeError: Cannot define property newProperty, object is not extensible
}
```
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263. ### What are the different ways to make an object non-extensible
You can mark an object non-extensible in 3 ways,
1. Object.preventExtensions
2. Object.seal
3. Object.freeze
```javascript
var newObject = {};
Object.preventExtensions(newObject); // Prevent objects are non-extensible
Object.isExtensible(newObject); // false
var sealedObject = Object.seal({}); // Sealed objects are non-extensible
Object.isExtensible(sealedObject); // false
var frozenObject = Object.freeze({}); // Frozen objects are non-extensible
Object.isExtensible(frozenObject); // false
```
**[⬆ Back to Top](#table-of-contents)**
264. ### How do you define multiple properties on an object
The `Object.defineProperties()` method is used to define new or modify existing properties directly on an object and returning the object. Let's define multiple properties on an empty object,
```javascript
const newObject = {};
Object.defineProperties(newObject, {
newProperty1: {
value: "John",
writable: true,
},
newProperty2: {},
});
```
**[⬆ Back to Top](#table-of-contents)**
265. ### What is MEAN in javascript
The MEAN (MongoDB, Express, AngularJS, and Node.js) stack is the most popular open-source JavaScript software tech stack available for building dynamic web apps where you can write both the server-side and client-side halves of the web project entirely in JavaScript.
**[⬆ Back to Top](#table-of-contents)**
266. ### What Is Obfuscation in javascript
Obfuscation is the deliberate act of creating obfuscated javascript code(i.e, source or machine code) that is difficult for humans to understand. It is something similar to encryption, but a machine can understand the code and execute it.
Let's see the below function before Obfuscation,
```javascript
function greeting() {
console.log("Hello, welcome to JS world");
}
```
And after the code Obfuscation, it would be appeared as below,
```javascript
eval(
(function (p, a, c, k, e, d) {
e = function (c) {
return c;
};
if (!"".replace(/^/, String)) {
while (c--) {
d[c] = k[c] || c;
}
k = [
function (e) {
return d[e];
},
];
e = function () {
return "\\w+";
};
c = 1;
}
while (c--) {
if (k[c]) {
p = p.replace(new RegExp("\\b" + e(c) + "\\b", "g"), k[c]);
}
}
return p;
})(
"2 1(){0.3('4, 7 6 5 8')}",
9,
9,
"console|greeting|function|log|Hello|JS|to|welcome|world".split("|"),
0,
{}
)
);
```
**[⬆ Back to Top](#table-of-contents)**
267. ### Why do you need Obfuscation
Below are the few reasons for Obfuscation,
1. The Code size will be reduced. So data transfers between server and client will be fast.
2. It hides the business logic from outside world and protects the code from others
3. Reverse engineering is highly difficult
4. The download time will be reduced
**[⬆ Back to Top](#table-of-contents)**
268. ### What is Minification
Minification is the process of removing all unnecessary characters(empty spaces are removed) and variables will be renamed without changing it's functionality. It is also a type of obfuscation .
**[⬆ Back to Top](#table-of-contents)**
269. ### What are the advantages of minification
Normally it is recommended to use minification for heavy traffic and intensive requirements of resources. It reduces file sizes with below benefits,
1. Decreases loading times of a web page
2. Saves bandwidth usages
**[⬆ Back to Top](#table-of-contents)**
270. ### What are the differences between Obfuscation and Encryption
Below are the main differences between Obfuscation and Encryption,
| Feature | Obfuscation | Encryption |
| ------------------ | ----------------------------------------------- | ----------------------------------------------------------------------- |
| Definition | Changing the form of any data in any other form | Changing the form of information to an unreadable format by using a key |
| A key to decode | It can be decoded without any key | It is required |
| Target data format | It will be converted to a complex form | Converted into an unreadable format |
**[⬆ Back to Top](#table-of-contents)**
271. ### What are the common tools used for minification
There are many online/offline tools to minify the javascript files,
1. Google's Closure Compiler
2. UglifyJS2
3. jsmin
4. javascript-minifier.com/
5. prettydiff.com
**[⬆ Back to Top](#table-of-contents)**
272. ### How do you perform form validation using javascript
JavaScript can be used to perform HTML form validation. For example, if the form field is empty, the function needs to notify, and return false, to prevent the form being submitted.
Lets' perform user login in an html form,
```html
<form name="myForm" onsubmit="return validateForm()" method="post">
User name: <input type="text" name="uname" />
<input type="submit" value="Submit" />
</form>
```
And the validation on user login is below,
```javascript
function validateForm() {
var x = document.forms["myForm"]["uname"].value;
if (x == "") {
alert("The username shouldn't be empty");
return false;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
273. ### How do you perform form validation without javascript
You can perform HTML form validation automatically without using javascript. The validation enabled by applying the `required` attribute to prevent form submission when the input is empty.
```html
<form method="post">
<input type="text" name="uname" required />
<input type="submit" value="Submit" />
</form>
```
**Note:** Automatic form validation does not work in Internet Explorer 9 or earlier.
**[⬆ Back to Top](#table-of-contents)**
274. ### What are the DOM methods available for constraint validation
The below DOM methods are available for constraint validation on an invalid input,
1. checkValidity(): It returns true if an input element contains valid data.
2. setCustomValidity(): It is used to set the validationMessage property of an input element.
Let's take an user login form with DOM validations
```javascript
function myFunction() {
var userName = document.getElementById("uname");
if (!userName.checkValidity()) {
document.getElementById("message").innerHTML =
userName.validationMessage;
} else {
document.getElementById("message").innerHTML =
"Entered a valid username";
}
}
```
**[⬆ Back to Top](#table-of-contents)**
275. ### What are the available constraint validation DOM properties
Below are the list of some of the constraint validation DOM properties available,
1. validity: It provides a list of boolean properties related to the validity of an input element.
2. validationMessage: It displays the message when the validity is false.
3. willValidate: It indicates if an input element will be validated or not.
**[⬆ Back to Top](#table-of-contents)**
276. ### What are the list of validity properties
The validity property of an input element provides a set of properties related to the validity of data.
1. customError: It returns true, if a custom validity message is set.
2. patternMismatch: It returns true, if an element's value does not match its pattern attribute.
3. rangeOverflow: It returns true, if an element's value is greater than its max attribute.
4. rangeUnderflow: It returns true, if an element's value is less than its min attribute.
5. stepMismatch: It returns true, if an element's value is invalid according to step attribute.
6. tooLong: It returns true, if an element's value exceeds its maxLength attribute.
7. typeMismatch: It returns true, if an element's value is invalid according to type attribute.
8. valueMissing: It returns true, if an element with a required attribute has no value.
9. valid: It returns true, if an element's value is valid.
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277. ### Give an example usage of rangeOverflow property
If an element's value is greater than its max attribute then rangeOverflow property returns true. For example, the below form submission throws an error if the value is more than 100,
```html
<input id="age" type="number" max="100" />
<button onclick="myOverflowFunction()">OK</button>
```
```javascript
function myOverflowFunction() {
if (document.getElementById("age").validity.rangeOverflow) {
alert("The mentioned age is not allowed");
}
}
```
**[⬆ Back to Top](#table-of-contents)**
278. ### Is enums feature available in javascript
No, javascript does not natively support enums. But there are different kinds of solutions to simulate them even though they may not provide exact equivalents. For example, you can use freeze or seal on object,
```javascript
var DaysEnum = Object.freeze({"monday":1, "tuesday":2, "wednesday":3, ...})
```
**[⬆ Back to Top](#table-of-contents)**
279. ### What is an enum
An enum is a type restricting variables to one value from a predefined set of constants. JavaScript has no enums but typescript provides built-in enum support.
```javascript
enum Color {
RED, GREEN, BLUE
}
```
**[⬆ Back to Top](#table-of-contents)**
280. ### How do you list all properties of an object
You can use the `Object.getOwnPropertyNames()` method which returns an array of all properties found directly in a given object. Let's the usage of it in an example,
```javascript
const newObject = {
a: 1,
b: 2,
c: 3,
};
console.log(Object.getOwnPropertyNames(newObject));
["a", "b", "c"];
```
**[⬆ Back to Top](#table-of-contents)**
281. ### How do you get property descriptors of an object
You can use the `Object.getOwnPropertyDescriptors()` method which returns all own property descriptors of a given object. The example usage of this method is below,
```javascript
const newObject = {
a: 1,
b: 2,
c: 3,
};
const descriptorsObject = Object.getOwnPropertyDescriptors(newObject);
console.log(descriptorsObject.a.writable); //true
console.log(descriptorsObject.a.configurable); //true
console.log(descriptorsObject.a.enumerable); //true
console.log(descriptorsObject.a.value); // 1
```
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282. ### What are the attributes provided by a property descriptor
A property descriptor is a record which has the following attributes
1. value: The value associated with the property
2. writable: Determines whether the value associated with the property can be changed or not
3. configurable: Returns true if the type of this property descriptor can be changed and if the property can be deleted from the corresponding object.
4. enumerable: Determines whether the property appears during enumeration of the properties on the corresponding object or not.
5. set: A function which serves as a setter for the property
6. get: A function which serves as a getter for the property
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283. ### How do you extend classes
The `extends` keyword is used in class declarations/expressions to create a class which is a child of another class. It can be used to subclass custom classes as well as built-in objects. The syntax would be as below,
```javascript
class ChildClass extends ParentClass { ... }
```
Let's take an example of Square subclass from Polygon parent class,
```javascript
class Square extends Rectangle {
constructor(length) {
super(length, length);
this.name = "Square";
}
get area() {
return this.width * this.height;
}
set area(value) {
this.area = value;
}
}
```
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284. ### How do I modify the url without reloading the page
The `window.location.href` property will be helpful to modify the url but it reloads the page. HTML5 introduced the `history.pushState()` and `history.replaceState()` methods, which allow you to add and modify history entries, respectively. For example, you can use pushState as below,
```javascript
window.history.pushState("page2", "Title", "/page2.html");
```
**[⬆ Back to Top](#table-of-contents)**
285. ### How do you check whether an array includes a particular value or not
The `Array#includes()` method is used to determine whether an array includes a particular value among its entries by returning either true or false. Let's see an example to find an element(numeric and string) within an array.
```javascript
var numericArray = [1, 2, 3, 4];
console.log(numericArray.includes(3)); // true
var stringArray = ["green", "yellow", "blue"];
console.log(stringArray.includes("blue")); //true
```
**[⬆ Back to Top](#table-of-contents)**
286. ### How do you compare scalar arrays
You can use length and every method of arrays to compare two scalar(compared directly using ===) arrays. The combination of these expressions can give the expected result,
```javascript
const arrayFirst = [1, 2, 3, 4, 5];
const arraySecond = [1, 2, 3, 4, 5];
console.log(
arrayFirst.length === arraySecond.length &&
arrayFirst.every((value, index) => value === arraySecond[index])
); // true
```
If you would like to compare arrays irrespective of order then you should sort them before,
```javascript
const arrayFirst = [2, 3, 1, 4, 5];
const arraySecond = [1, 2, 3, 4, 5];
console.log(
arrayFirst.length === arraySecond.length &&
arrayFirst.sort().every((value, index) => value === arraySecond[index])
); //true
```
**[⬆ Back to Top](#table-of-contents)**
287. ### How to get the value from get parameters
The `new URL()` object accepts the url string and `searchParams` property of this object can be used to access the get parameters. Remember that you may need to use polyfill or `window.location` to access the URL in older browsers(including IE).
```javascript
let urlString = "http://www.some-domain.com/about.html?x=1&y=2&z=3"; //window.location.href
let url = new URL(urlString);
let parameterZ = url.searchParams.get("z");
console.log(parameterZ); // 3
```
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288. ### How do you print numbers with commas as thousand separators
You can use the `Number.prototype.toLocaleString()` method which returns a string with a language-sensitive representation such as thousand separator,currency etc of this number.
```javascript
function convertToThousandFormat(x) {
return x.toLocaleString(); // 12,345.679
}
console.log(convertToThousandFormat(12345.6789));
```
**[⬆ Back to Top](#table-of-contents)**
289. ### What is the difference between java and javascript
Both are totally unrelated programming languages and no relation between them. Java is statically typed, compiled, runs on its own VM. Whereas Javascript is dynamically typed, interpreted, and runs in a browser and nodejs environments. Let's see the major differences in a tabular format,
| Feature | Java | JavaScript |
|---- | ---- | -----
| Typed | It's a strongly typed language | It's a dynamic typed language |
| Paradigm | Object oriented programming | Prototype based programming |
| Scoping | Block scoped | Function-scoped |
| Concurrency | Thread based | event based |
| Memory | Uses more memory | Uses less memory. Hence it will be used for web pages |
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290. ### Does JavaScript supports namespace
JavaScript doesn’t support namespace by default. So if you create any element(function, method, object, variable) then it becomes global and pollutes the global namespace. Let's take an example of defining two functions without any namespace,
```javascript
function func1() {
console.log("This is a first definition");
}
function func1() {
console.log("This is a second definition");
}
func1(); // This is a second definition
```
It always calls the second function definition. In this case, namespace will solve the name collision problem.
**[⬆ Back to Top](#table-of-contents)**
291. ### How do you declare namespace
Even though JavaScript lacks namespaces, we can use Objects , IIFE to create namespaces.
1. **Using Object Literal Notation:** Let's wrap variables and functions inside an Object literal which acts as a namespace. After that you can access them using object notation
```javascript
var namespaceOne = {
function func1() {
console.log("This is a first definition");
}
}
var namespaceTwo = {
function func1() {
console.log("This is a second definition");
}
}
namespaceOne.func1(); // This is a first definition
namespaceTwo.func1(); // This is a second definition
```
1. **Using IIFE (Immediately invoked function expression):** The outer pair of parentheses of IIFE creates a local scope for all the code inside of it and makes the anonymous function a function expression. Due to that, you can create the same function in two different function expressions to act as a namespace.
```javascript
(function () {
function fun1() {
console.log("This is a first definition");
}
fun1();
})();
(function () {
function fun1() {
console.log("This is a second definition");
}
fun1();
})();
```
1. **Using a block and a let/const declaration:** In ECMAScript 6, you can simply use a block and a let declaration to restrict the scope of a variable to a block.
```javascript
{
let myFunction = function fun1() {
console.log("This is a first definition");
};
myFunction();
}
//myFunction(): ReferenceError: myFunction is not defined.
{
let myFunction = function fun1() {
console.log("This is a second definition");
};
myFunction();
}
//myFunction(): ReferenceError: myFunction is not defined.
```
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292. ### How do you invoke javascript code in an iframe from parent page
Initially iFrame needs to be accessed using either `document.getElementBy` or `window.frames`. After that `contentWindow` property of iFrame gives the access for targetFunction
```javascript
document.getElementById("targetFrame").contentWindow.targetFunction();
window.frames[0].frameElement.contentWindow.targetFunction(); // Accessing iframe this way may not work in latest versions chrome and firefox
```
**[⬆ Back to Top](#table-of-contents)**
293. ### How do get the timezone offset from date
You can use the `getTimezoneOffset` method of the date object. This method returns the time zone difference, in minutes, from current locale (host system settings) to UTC
```javascript
var offset = new Date().getTimezoneOffset();
console.log(offset); // -480
```
**[⬆ Back to Top](#table-of-contents)**
294. ### How do you load CSS and JS files dynamically
You can create both link and script elements in the DOM and append them as child to head tag. Let's create a function to add script and style resources as below,
```javascript
function loadAssets(filename, filetype) {
if (filetype == "css") {
// External CSS file
var fileReference = document.createElement("link");
fileReference.setAttribute("rel", "stylesheet");
fileReference.setAttribute("type", "text/css");
fileReference.setAttribute("href", filename);
} else if (filetype == "js") {
// External JavaScript file
var fileReference = document.createElement("script");
fileReference.setAttribute("type", "text/javascript");
fileReference.setAttribute("src", filename);
}
if (typeof fileReference != "undefined")
document.getElementsByTagName("head")[0].appendChild(fileReference);
}
```
**[⬆ Back to Top](#table-of-contents)**
295. ### What are the different methods to find HTML elements in DOM
If you want to access any element in an HTML page, you need to start with accessing the document object. Later you can use any of the below methods to find the HTML element,
1. document.getElementById(id): It finds an element by Id
2. document.getElementsByTagName(name): It finds an element by tag name
3. document.getElementsByClassName(name): It finds an element by class name
**[⬆ Back to Top](#table-of-contents)**
296. ### What is jQuery
jQuery is a popular cross-browser JavaScript library that provides Document Object Model (DOM) traversal, event handling, animations and AJAX interactions by minimizing the discrepancies across browsers. It is widely famous with its philosophy of “Write less, do more”. For example, you can display welcome message on the page load using jQuery as below,
```javascript
$(document).ready(function () {
// It selects the document and apply the function on page load
alert("Welcome to jQuery world");
});
```
**Note:** You can download it from jquery's official site or install it from CDNs, like google.
**[⬆ Back to Top](#table-of-contents)**
297. ### What is V8 JavaScript engine
V8 is an open source high-performance JavaScript engine used by the Google Chrome browser, written in C++. It is also being used in the node.js project. It implements ECMAScript and WebAssembly, and runs on Windows 7 or later, macOS 10.12+, and Linux systems that use x64, IA-32, ARM, or MIPS processors.
**Note:** It can run standalone, or can be embedded into any C++ application.
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298. ### Why do we call javascript as dynamic language
JavaScript is a loosely typed or a dynamic language because variables in JavaScript are not directly associated with any particular value type, and any variable can be assigned/reassigned with values of all types.
```javascript
let age = 50; // age is a number now
age = "old"; // age is a string now
age = true; // age is a boolean
```
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299. ### What is a void operator
The `void` operator evaluates the given expression and then returns undefined(i.e, without returning value). The syntax would be as below,
```javascript
void expression;
void expression;
```
Let's display a message without any redirection or reload
```javascript
<a href="javascript:void(alert('Welcome to JS world'))">
Click here to see a message
</a>
```
**Note:** This operator is often used to obtain the undefined primitive value, using "void(0)".
**[⬆ Back to Top](#table-of-contents)**
300. ### How to set the cursor to wait
The cursor can be set to wait in JavaScript by using the property "cursor". Let's perform this behavior on page load using the below function.
```javascript
function myFunction() {
window.document.body.style.cursor = "wait";
}
```
and this function invoked on page load
```html
<body onload="myFunction()"></body>
```
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301. ### How do you create an infinite loop
You can create infinite loops using for and while loops without using any expressions. The for loop construct or syntax is better approach in terms of ESLint and code optimizer tools,
```javascript
for (;;) {}
while (true) {}
```
**[⬆ Back to Top](#table-of-contents)**
302. ### Why do you need to avoid with statement
JavaScript's with statement was intended to provide a shorthand for writing recurring accesses to objects. So it can help reduce file size by reducing the need to repeat a lengthy object reference without performance penalty. Let's take an example where it is used to avoid redundancy when accessing an object several times.
```javascript
a.b.c.greeting = "welcome";
a.b.c.age = 32;
```
Using `with` it turns this into:
```javascript
with (a.b.c) {
greeting = "welcome";
age = 32;
}
```
But this `with` statement creates performance problems since one cannot predict whether an argument will refer to a real variable or to a property inside the with argument.
**[⬆ Back to Top](#table-of-contents)**
303. ### What is the output of below for loops
```javascript
for (var i = 0; i < 4; i++) {
// global scope
setTimeout(() => console.log(i));
}
for (let i = 0; i < 4; i++) {
// block scope
setTimeout(() => console.log(i));
}
```
The output of the above for loops is 4 4 4 4 and 0 1 2 3
**Explanation:** Due to the event queue/loop of javascript, the `setTimeout` callback function is called after the loop has been executed. Since the variable i is declared with the `var` keyword it became a global variable and the value was equal to 4 using iteration when the time `setTimeout` function is invoked. Hence, the output of the first loop is `4 4 4 4`.
Whereas in the second loop, the variable i is declared as the `let` keyword it becomes a block scoped variable and it holds a new value(0, 1 ,2 3) for each iteration. Hence, the output of the first loop is `0 1 2 3`.
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304. ### List down some of the features of ES6
Below are the list of some new features of ES6,
1. Support for constants or immutable variables
2. Block-scope support for variables, constants and functions
3. Arrow functions
4. Default parameters
5. Rest and Spread Parameters
6. Template Literals
7. Multi-line Strings
8. Destructuring Assignment
9. Enhanced Object Literals
10. Promises
11. Classes
12. Modules
**[⬆ Back to Top](#table-of-contents)**
305. ### What is ES6
ES6 is the sixth edition of the javascript language and it was released in June 2015. It was initially known as ECMAScript 6 (ES6) and later renamed to ECMAScript 2015. Almost all the modern browsers support ES6 but for the old browsers there are many transpilers, like Babel.js etc.
**[⬆ Back to Top](#table-of-contents)**
306. ### Can I redeclare let and const variables
No, you cannot redeclare let and const variables. If you do, it throws below error
```bash
Uncaught SyntaxError: Identifier 'someVariable' has already been declared
```
**Explanation:** The variable declaration with `var` keyword refers to a function scope and the variable is treated as if it were declared at the top of the enclosing scope due to hoisting feature. So all the multiple declarations contributing to the same hoisted variable without any error. Let's take an example of re-declaring variables in the same scope for both var and let/const variables.
```javascript
var name = "John";
function myFunc() {
var name = "Nick";
var name = "Abraham"; // Re-assigned in the same function block
alert(name); // Abraham
}
myFunc();
alert(name); // John
```
The block-scoped multi-declaration throws syntax error,
```javascript
let name = "John";
function myFunc() {
let name = "Nick";
let name = "Abraham"; // Uncaught SyntaxError: Identifier 'name' has already been declared
alert(name);
}
myFunc();
alert(name);
```
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307. ### Is const variable makes the value immutable
No, the const variable doesn't make the value immutable. But it disallows subsequent assignments(i.e, You can declare with assignment but can't assign another value later)
```javascript
const userList = [];
userList.push("John"); // Can mutate even though it can't re-assign
console.log(userList); // ['John']
```
**[⬆ Back to Top](#table-of-contents)**
308. ### What are default parameters
In ES5, we need to depend on logical OR operators to handle default values of function parameters. Whereas in ES6, Default function parameters feature allows parameters to be initialized with default values if no value or undefined is passed. Let's compare the behavior with an examples,
```javascript
//ES5
var calculateArea = function (height, width) {
height = height || 50;
width = width || 60;
return width * height;
};
console.log(calculateArea()); //300
```
The default parameters makes the initialization more simpler,
```javascript
//ES6
var calculateArea = function (height = 50, width = 60) {
return width * height;
};
console.log(calculateArea()); //300
```
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309. ### What are template literals
Template literals or template strings are string literals allowing embedded expressions. These are enclosed by the back-tick (`) character instead of double or single quotes.
In ES6, this feature enables using dynamic expressions as below,
```javascript
var greeting = `Welcome to JS World, Mr. ${firstName} ${lastName}.`;
```
In ES5, you need break string like below,
```javascript
var greeting = 'Welcome to JS World, Mr. ' + firstName + ' ' + lastName.`
```
**Note:** You can use multi-line strings and string interpolation features with template literals.
**[⬆ Back to Top](#table-of-contents)**
310. ### How do you write multi-line strings in template literals
In ES5, you would have to use newline escape characters('\\n') and concatenation symbols(+) in order to get multi-line strings.
```javascript
console.log("This is string sentence 1\n" + "This is string sentence 2");
```
Whereas in ES6, You don't need to mention any newline sequence character,
```javascript
console.log(`This is string sentence
'This is string sentence 2`);
```
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311. ### What are nesting templates
The nesting template is a feature supported within template literals syntax to allow inner backticks inside a placeholder ${ } within the template. For example, the below nesting template is used to display the icons based on user permissions whereas outer template checks for platform type,
```javascript
const iconStyles = `icon ${
isMobilePlatform()
? ""
: `icon-${user.isAuthorized ? "submit" : "disabled"}`
}`;
```
You can write the above use case without nesting template features as well. However, the nesting template feature is more compact and readable.
```javascript
//Without nesting templates
const iconStyles = `icon ${
isMobilePlatform()
? ""
: user.isAuthorized
? "icon-submit"
: "icon-disabled"
}`;
```
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312. ### What are tagged templates
Tagged templates are the advanced form of templates in which tags allow you to parse template literals with a function. The tag function accepts the first parameter as an array of strings and remaining parameters as expressions. This function can also return manipulated strings based on parameters. Let's see the usage of this tagged template behavior of an IT professional skill set in an organization,
```javascript
var user1 = "John";
var skill1 = "JavaScript";
var experience1 = 15;
var user2 = "Kane";
var skill2 = "JavaScript";
var experience2 = 5;
function myInfoTag(strings, userExp, experienceExp, skillExp) {
var str0 = strings[0]; // "Mr/Ms. "
var str1 = strings[1]; // " is a/an "
var str2 = strings[2]; // "in"
var expertiseStr;
if (experienceExp > 10) {
expertiseStr = "expert developer";
} else if (skillExp > 5 && skillExp <= 10) {
expertiseStr = "senior developer";
} else {
expertiseStr = "junior developer";
}
return `${str0}${userExp}${str1}${expertiseStr}${str2}${skillExp}`;
}
var output1 = myInfoTag`Mr/Ms. ${user1} is a/an ${experience1} in ${skill1}`;
var output2 = myInfoTag`Mr/Ms. ${user2} is a/an ${experience2} in ${skill2}`;
console.log(output1); // Mr/Ms. John is a/an expert developer in JavaScript
console.log(output2); // Mr/Ms. Kane is a/an junior developer in JavaScript
```
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313. ### What are raw strings
ES6 provides a raw strings feature using the `String.raw()` method which is used to get the raw string form of template strings. This feature allows you to access the raw strings as they were entered, without processing escape sequences. For example, the usage would be as below,
```javascript
var calculationString = String.raw`The sum of numbers is \n${
1 + 2 + 3 + 4
}!`;
console.log(calculationString); // The sum of numbers is \n10!
```
If you don't use raw strings, the newline character sequence will be processed by displaying the output in multiple lines
```javascript
var calculationString = `The sum of numbers is \n${1 + 2 + 3 + 4}!`;
console.log(calculationString);
// The sum of numbers is
// 10!
```
Also, the raw property is available on the first argument to the tag function
```javascript
function tag(strings) {
console.log(strings.raw[0]);
}
```
**[⬆ Back to Top](#table-of-contents)**
314. ### What is destructuring assignment
The destructuring assignment is a JavaScript expression that makes it possible to unpack values from arrays or properties from objects into distinct variables.
Let's get the month values from an array using destructuring assignment
```javascript
var [one, two, three] = ["JAN", "FEB", "MARCH"];
console.log(one); // "JAN"
console.log(two); // "FEB"
console.log(three); // "MARCH"
```
and you can get user properties of an object using destructuring assignment,
```javascript
var { name, age } = { name: "John", age: 32 };
console.log(name); // John
console.log(age); // 32
```
**[⬆ Back to Top](#table-of-contents)**
315. ### What are default values in destructuring assignment
A variable can be assigned a default value when the value unpacked from the array or object is undefined during destructuring assignment. It helps to avoid setting default values separately for each assignment. Let's take an example for both arrays and object use cases,
**Arrays destructuring:**
```javascript
var x, y, z;
[x = 2, y = 4, z = 6] = [10];
console.log(x); // 10
console.log(y); // 4
console.log(z); // 6
```
**Objects destructuring:**
```javascript
var { x = 2, y = 4, z = 6 } = { x: 10 };
console.log(x); // 10
console.log(y); // 4
console.log(z); // 6
```
**[⬆ Back to Top](#table-of-contents)**
316. ### How do you swap variables in destructuring assignment
If you don't use destructuring assignment, swapping two values requires a temporary variable. Whereas using a destructuring feature, two variable values can be swapped in one destructuring expression. Let's swap two number variables in array destructuring assignment,
```javascript
var x = 10,
y = 20;
[x, y] = [y, x];
console.log(x); // 20
console.log(y); // 10
```
**[⬆ Back to Top](#table-of-contents)**
317. ### What are enhanced object literals
Object literals make it easy to quickly create objects with properties inside the curly braces. For example, it provides shorter syntax for common object property definition as below.
```javascript
//ES6
var x = 10,
y = 20;
obj = { x, y };
console.log(obj); // {x: 10, y:20}
//ES5
var x = 10,
y = 20;
obj = { x: x, y: y };
console.log(obj); // {x: 10, y:20}
```
**[⬆ Back to Top](#table-of-contents)**
318. ### What are dynamic imports
The dynamic imports using `import()` function syntax allows us to load modules on demand by using promises or the async/await syntax. Currently this feature is in [stage4 proposal](https://github.com/tc39/proposal-dynamic-import). The main advantage of dynamic imports is reduction of our bundle's sizes, the size/payload response of our requests and overall improvements in the user experience.
The syntax of dynamic imports would be as below,
```javascript
import("./Module").then((Module) => Module.method());
```
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319. ### What are the use cases for dynamic imports
Below are some of the use cases of using dynamic imports over static imports,
1. Import a module on-demand or conditionally. For example, if you want to load a polyfill on legacy browser
```javascript
if (isLegacyBrowser()) {
import(···)
.then(···);
}
```
1. Compute the module specifier at runtime. For example, you can use it for internationalization.
```javascript
import(`messages_${getLocale()}.js`).then(···);
```
1. Import a module from within a regular script instead a module.
**[⬆ Back to Top](#table-of-contents)**
320. ### What are typed arrays
Typed arrays are array-like objects from ECMAScript 6 API for handling binary data. JavaScript provides 8 Typed array types,
1. Int8Array: An array of 8-bit signed integers
2. Int16Array: An array of 16-bit signed integers
3. Int32Array: An array of 32-bit signed integers
4. Uint8Array: An array of 8-bit unsigned integers
5. Uint16Array: An array of 16-bit unsigned integers
6. Uint32Array: An array of 32-bit unsigned integers
7. Float32Array: An array of 32-bit floating point numbers
8. Float64Array: An array of 64-bit floating point numbers
For example, you can create an array of 8-bit signed integers as below
```javascript
const a = new Int8Array();
// You can pre-allocate n bytes
const bytes = 1024;
const a = new Int8Array(bytes);
```
**[⬆ Back to Top](#table-of-contents)**
321. ### What are the advantages of module loaders
The module loaders provides the below features,
1. Dynamic loading
2. State isolation
3. Global namespace isolation
4. Compilation hooks
5. Nested virtualization
**[⬆ Back to Top](#table-of-contents)**
322. ### What is collation
Collation is used for sorting a set of strings and searching within a set of strings. It is parameterized by locale and aware of Unicode. Let's take comparison and sorting features,
1. **Comparison:**
```javascript
var list = ["ä", "a", "z"]; // In German, "ä" sorts with "a" Whereas in Swedish, "ä" sorts after "z"
var l10nDE = new Intl.Collator("de");
var l10nSV = new Intl.Collator("sv");
console.log(l10nDE.compare("ä", "z") === -1); // true
console.log(l10nSV.compare("ä", "z") === +1); // true
```
1. **Sorting:**
```javascript
var list = ["ä", "a", "z"]; // In German, "ä" sorts with "a" Whereas in Swedish, "ä" sorts after "z"
var l10nDE = new Intl.Collator("de");
var l10nSV = new Intl.Collator("sv");
console.log(list.sort(l10nDE.compare)); // [ "a", "ä", "z" ]
console.log(list.sort(l10nSV.compare)); // [ "a", "z", "ä" ]
```
**[⬆ Back to Top](#table-of-contents)**
323. ### What is for...of statement
The for...of statement creates a loop iterating over iterable objects or elements such as built-in String, Array, Array-like objects (like arguments or NodeList), TypedArray, Map, Set, and user-defined iterables. The basic usage of for...of statement on arrays would be as below,
```javascript
let arrayIterable = [10, 20, 30, 40, 50];
for (let value of arrayIterable) {
value++;
console.log(value); // 11 21 31 41 51
}
```
**[⬆ Back to Top](#table-of-contents)**
324. ### What is the output of below spread operator array
```javascript
[..."John Resig"];
```
The output of the array is ['J', 'o', 'h', 'n', '', 'R', 'e', 's', 'i', 'g']
**Explanation:** The string is an iterable type and the spread operator within an array maps every character of an iterable to one element. Hence, each character of a string becomes an element within an Array.
**[⬆ Back to Top](#table-of-contents)**
325. ### Is PostMessage secure
Yes, postMessages can be considered very secure as long as the programmer/developer is careful about checking the origin and source of an arriving message. But if you try to send/receive a message without verifying its source will create cross-site scripting attacks.
**[⬆ Back to Top](#table-of-contents)**
326. ### What are the problems with postmessage target origin as wildcard
The second argument of postMessage method specifies which origin is allowed to receive the message. If you use the wildcard “\*” as an argument then any origin is allowed to receive the message. In this case, there is no way for the sender window to know if the target window is at the target origin when sending the message. If the target window has been navigated to another origin, the other origin would receive the data. Hence, this may lead to XSS vulnerabilities.
```javascript
targetWindow.postMessage(message, "*");
```
**[⬆ Back to Top](#table-of-contents)**
327. ### How do you avoid receiving postMessages from attackers
Since the listener listens for any message, an attacker can trick the application by sending a message from the attacker’s origin, which gives an impression that the receiver received the message from the actual sender’s window. You can avoid this issue by validating the origin of the message on the receiver's end using the “message.origin” attribute. For examples, let's check the sender's origin [http://www.some-sender.com](http://www.some-sender.com) on receiver side [www.some-receiver.com](www.some-receiver.com),
```javascript
//Listener on http://www.some-receiver.com/
window.addEventListener("message", function(message){
if(/^http://www\.some-sender\.com$/.test(message.origin)){
console.log('You received the data from valid sender', message.data);
}
});
```
**[⬆ Back to Top](#table-of-contents)**
328. ### Can I avoid using postMessages completely
You cannot avoid using postMessages completely(or 100%). Even though your application doesn’t use postMessage considering the risks, a lot of third party scripts use postMessage to communicate with the third party service. So your application might be using postMessage without your knowledge.
**[⬆ Back to Top](#table-of-contents)**
329. ### Is postMessages synchronous
The postMessages are synchronous in IE8 browser but they are asynchronous in IE9 and all other modern browsers (i.e, IE9+, Firefox, Chrome, Safari).Due to this asynchronous behaviour, we use a callback mechanism when the postMessage is returned.
**[⬆ Back to Top](#table-of-contents)**
330. ### What paradigm is Javascript
JavaScript is a multi-paradigm language, supporting imperative/procedural programming, Object-Oriented Programming and functional programming. JavaScript supports Object-Oriented Programming with prototypical inheritance.
**[⬆ Back to Top](#table-of-contents)**
331. ### What is the difference between internal and external javascript
**Internal JavaScript:** It is the source code within the script tag.
**External JavaScript:** The source code is stored in an external file(stored with .js extension) and referred with in the tag.
**[⬆ Back to Top](#table-of-contents)**
332. ### Is JavaScript faster than server side script
Yes, JavaScript is faster than server side scripts. Because JavaScript is a client-side script it does not require any web server’s help for its computation or calculation. So JavaScript is always faster than any server-side script like ASP, PHP, etc.
**[⬆ Back to Top](#table-of-contents)**
333. ### How do you get the status of a checkbox
You can apply the `checked` property on the selected checkbox in the DOM. If the value is `true` it means the checkbox is checked, otherwise it is unchecked. For example, the below HTML checkbox element can be access using javascript as below:
```html
<input type="checkbox" id="checkboxname" value="Agree" /> Agree the
conditions<br />
```
```javascript
console.log(document.getElementById(‘checkboxname’).checked); // true or false
```
**[⬆ Back to Top](#table-of-contents)**
334. ### What is the purpose of double tilde operator
The double tilde operator(~~) is known as double NOT bitwise operator. This operator is a slightly quicker substitute for Math.floor().
**[⬆ Back to Top](#table-of-contents)**
335. ### How do you convert character to ASCII code
You can use the `String.prototype.charCodeAt()` method to convert string characters to ASCII numbers. For example, let's find ASCII code for the first letter of 'ABC' string,
```javascript
"ABC".charCodeAt(0); // returns 65
```
Whereas `String.fromCharCode()` method converts numbers to equal ASCII characters.
```javascript
String.fromCharCode(65, 66, 67); // returns 'ABC'
```
**[⬆ Back to Top](#table-of-contents)**
336. ### What is ArrayBuffer
An ArrayBuffer object is used to represent a generic, fixed-length raw binary data buffer. You can create it as below,
```javascript
let buffer = new ArrayBuffer(16); // create a buffer of length 16
alert(buffer.byteLength); // 16
```
To manipulate an ArrayBuffer, we need to use a “view” object.
```javascript
//Create a DataView referring to the buffer
let view = new DataView(buffer);
```
**[⬆ Back to Top](#table-of-contents)**
337. ### What is the output of below string expression
```javascript
console.log("Welcome to JS world"[0]);
```
The output of the above expression is "W".
**Explanation:** The bracket notation with specific index on a string returns the character at a specific location. Hence, it returns the character "W" of the string. Since this is not supported in IE7 and below versions, you may need to use the .charAt() method to get the desired result.
**[⬆ Back to Top](#table-of-contents)**
338. ### What is the purpose of Error object
The Error constructor creates an error object and the instances of error objects are thrown when runtime errors occur. The Error object can also be used as a base object for user-defined exceptions. The syntax of error object would be as below,
```javascript
new Error([message[, fileName[, lineNumber]]])
```
You can throw user defined exceptions or errors using Error object in try...catch block as below,
```javascript
try {
if (withdraw > balance)
throw new Error("Oops! You don't have enough balance");
} catch (e) {
console.log(e.name + ": " + e.message);
}
```
**[⬆ Back to Top](#table-of-contents)**
339. ### What is the purpose of EvalError object
The EvalError object indicates an error regarding the global `eval()` function. Even though this exception is not thrown by JavaScript anymore, the EvalError object remains for compatibility. The syntax of this expression would be as below,
```javascript
new EvalError([message[, fileName[, lineNumber]]])
```
You can throw EvalError with in try...catch block as below,
```javascript
try {
throw new EvalError('Eval function error', 'someFile.js', 100);
} catch (e) {
console.log(e.message, e.name, e.fileName); // "Eval function error", "EvalError", "someFile.js"
```
**[⬆ Back to Top](#table-of-contents)**
340. ### What are the list of cases error thrown from non-strict mode to strict mode
When you apply 'use strict'; syntax, some of the below cases will throw a SyntaxError before executing the script
1. When you use Octal syntax
```javascript
var n = 022;
```
1. Using `with` statement
2. When you use delete operator on a variable name
3. Using eval or arguments as variable or function argument name
4. When you use newly reserved keywords
5. When you declare a function in a block
```javascript
if (someCondition) {
function f() {}
}
```
Hence, the errors from above cases are helpful to avoid errors in development/production environments.
**[⬆ Back to Top](#table-of-contents)**
341. ### Do all objects have prototypes
No. All objects have prototypes except for the base object which is created by the user, or an object that is created using the new keyword.
**[⬆ Back to Top](#table-of-contents)**
342. ### What is the difference between a parameter and an argument
Parameter is the variable name of a function definition whereas an argument represents the value given to a function when it is invoked. Let's explain this with a simple function
```javascript
function myFunction(parameter1, parameter2, parameter3) {
console.log(arguments[0]); // "argument1"
console.log(arguments[1]); // "argument2"
console.log(arguments[2]); // "argument3"
}
myFunction("argument1", "argument2", "argument3");
```
**[⬆ Back to Top](#table-of-contents)**
343. ### What is the purpose of some method in arrays
The some() method is used to test whether at least one element in the array passes the test implemented by the provided function. The method returns a boolean value. Let's take an example to test for any odd elements,
```javascript
var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var odd = (element) => element % 2 !== 0;
console.log(array.some(odd)); // true (the odd element exists)
```
**[⬆ Back to Top](#table-of-contents)**
344. ### How do you combine two or more arrays
The concat() method is used to join two or more arrays by returning a new array containing all the elements. The syntax would be as below,
```javascript
array1.concat(array2, array3, ..., arrayX)
```
Let's take an example of array's concatenation with veggies and fruits arrays,
```javascript
var veggies = ["Tomato", "Carrot", "Cabbage"];
var fruits = ["Apple", "Orange", "Pears"];
var veggiesAndFruits = veggies.concat(fruits);
console.log(veggiesAndFruits); // Tomato, Carrot, Cabbage, Apple, Orange, Pears
```
**[⬆ Back to Top](#table-of-contents)**
345. ### What is the difference between Shallow and Deep copy
There are two ways to copy an object,
**Shallow Copy:**
Shallow copy is a bitwise copy of an object. A new object is created that has an exact copy of the values in the original object. If any of the fields of the object are references to other objects, just the reference addresses are copied i.e., only the memory address is copied.
**Example**
```javascript
var empDetails = {
name: "John",
age: 25,
expertise: "Software Developer",
};
```
to create a duplicate
```javascript
var empDetailsShallowCopy = empDetails; //Shallow copying!
```
if we change some property value in the duplicate one like this:
```javascript
empDetailsShallowCopy.name = "Johnson";
```
The above statement will also change the name of `empDetails`, since we have a shallow copy. That means we're losing the original data as well.
**Deep copy:**
A deep copy copies all fields, and makes copies of dynamically allocated memory pointed to by the fields. A deep copy occurs when an object is copied along with the objects to which it refers.
**Example**
```javascript
var empDetails = {
name: "John",
age: 25,
expertise: "Software Developer",
};
```
Create a deep copy by using the properties from the original object into new variable
```javascript
var empDetailsDeepCopy = {
name: empDetails.name,
age: empDetails.age,
expertise: empDetails.expertise,
};
```
Now if you change `empDetailsDeepCopy.name`, it will only affect `empDetailsDeepCopy` & not `empDetails`
**[⬆ Back to Top](#table-of-contents)**
346. ### How do you create specific number of copies of a string
The `repeat()` method is used to construct and return a new string which contains the specified number of copies of the string on which it was called, concatenated together. Remember that this method has been added to the ECMAScript 2015 specification.
Let's take an example of Hello string to repeat it 4 times,
```javascript
"Hello".repeat(4); // 'HelloHelloHelloHello'
```
347. ### How do you return all matching strings against a regular expression
The `matchAll()` method can be used to return an iterator of all results matching a string against a regular expression. For example, the below example returns an array of matching string results against a regular expression,
```javascript
let regexp = /Hello(\d?))/g;
let greeting = "Hello1Hello2Hello3";
let greetingList = [...greeting.matchAll(regexp)];
console.log(greetingList[0]); //Hello1
console.log(greetingList[1]); //Hello2
console.log(greetingList[2]); //Hello3
```
**[⬆ Back to Top](#table-of-contents)**
348. ### How do you trim a string at the beginning or ending
The `trim` method of string prototype is used to trim on both sides of a string. But if you want to trim especially at the beginning or ending of the string then you can use `trimStart/trimLeft` and `trimEnd/trimRight` methods. Let's see an example of these methods on a greeting message,
```javascript
var greeting = " Hello, Goodmorning! ";
console.log(greeting); // " Hello, Goodmorning! "
console.log(greeting.trimStart()); // "Hello, Goodmorning! "
console.log(greeting.trimLeft()); // "Hello, Goodmorning! "
console.log(greeting.trimEnd()); // " Hello, Goodmorning!"
console.log(greeting.trimRight()); // " Hello, Goodmorning!"
```
**[⬆ Back to Top](#table-of-contents)**
349. ### What is the output of below console statement with unary operator
Let's take console statement with unary operator as given below,
```javascript
console.log(+"Hello");
```
The output of the above console log statement returns NaN. Because the element is prefixed by the unary operator and the JavaScript interpreter will try to convert that element into a number type. Since the conversion fails, the value of the statement results in NaN value.
**[⬆ Back to Top](#table-of-contents)**
350. ### Does javascript uses mixins
Mixin is a generic object-oriented programming term - is a class containing methods that can be used by other classes without a need to inherit from it. In JavaScript we can only inherit from a single object. ie. There can be only one `[[prototype]]` for an object.
But sometimes we require to extend more than one, to overcome this we can use Mixin which helps to copy methods to the prototype of another class.
Say for instance, we've two classes `User` and `CleanRoom`. Suppose we need to add `CleanRoom` functionality to `User`, so that user can clean the room at demand. Here's where concept called mixins comes into picture.
```javascript
// mixin
let cleanRoomMixin = {
cleanRoom() {
alert(`Hello ${this.name}, your room is clean now`);
},
sayBye() {
alert(`Bye ${this.name}`);
},
};
// usage:
class User {
constructor(name) {
this.name = name;
}
}
// copy the methods
Object.assign(User.prototype, cleanRoomMixin);
// now User can clean the room
new User("Dude").cleanRoom(); // Hello Dude, your room is clean now!
```
**[⬆ Back to Top](#table-of-contents)**
351. ### What is a thunk function
A thunk is just a function which delays the evaluation of the value. It doesn’t take any arguments but gives the value whenever you invoke the thunk. i.e, It is used not to execute now but it will be sometime in the future. Let's take a synchronous example,
```javascript
const add = (x, y) => x + y;
const thunk = () => add(2, 3);
thunk(); // 5
```
**[⬆ Back to Top](#table-of-contents)**
352. ### What are asynchronous thunks
The asynchronous thunks are useful to make network requests. Let's see an example of network requests,
```javascript
function fetchData(fn) {
fetch("https://jsonplaceholder.typicode.com/todos/1")
.then((response) => response.json())
.then((json) => fn(json));
}
const asyncThunk = function () {
return fetchData(function getData(data) {
console.log(data);
});
};
asyncThunk();
```
The `getData` function won't be called immediately but it will be invoked only when the data is available from API endpoint. The setTimeout function is also used to make our code asynchronous. The best real time example is redux state management library which uses the asynchronous thunks to delay the actions to dispatch.
**[⬆ Back to Top](#table-of-contents)**
353. ### What is the output of below function calls
**Code snippet:**
```javascript
const circle = {
radius: 20,
diameter() {
return this.radius * 2;
},
perimeter: () => 2 * Math.PI * this.radius,
};
```
```javascript
console.log(circle.diameter());
console.log(circle.perimeter());
```
**Output:**
The output is 40 and NaN. Remember that diameter is a regular function, whereas the value of perimeter is an arrow function. The `this` keyword of a regular function(i.e, diameter) refers to the surrounding scope which is a class(i.e, Shape object). Whereas this keyword of perimeter function refers to the surrounding scope which is a window object. Since there is no radius property on window objects it returns an undefined value and the multiple of number value returns NaN value.
**[⬆ Back to Top](#table-of-contents)**
354. ### How to remove all line breaks from a string
The easiest approach is using regular expressions to detect and replace newlines in the string. In this case, we use replace function along with string to replace with, which in our case is an empty string.
```javascript
function remove_linebreaks( var message ) {
return message.replace( /[\r\n]+/gm, "" );
}
```
In the above expression, g and m are for global and multiline flags.
**[⬆ Back to Top](#table-of-contents)**
355. ### What is the difference between reflow and repaint
A _repaint_ occurs when changes are made which affect the visibility of an element, but not its layout. Examples of this include outline, visibility, or background color. A _reflow_ involves changes that affect the layout of a portion of the page (or the whole page). Resizing the browser window, changing the font, content changing (such as user typing text), using JavaScript methods involving computed styles, adding or removing elements from the DOM, and changing an element's classes are a few of the things that can trigger reflow. Reflow of an element causes the subsequent reflow of all child and ancestor elements as well as any elements following it in the DOM.
**[⬆ Back to Top](#table-of-contents)**
356. ### What happens with negating an array
Negating an array with `!` character will coerce the array into a boolean. Since Arrays are considered to be truthy So negating it will return `false`.
```javascript
console.log(![]); // false
```
**[⬆ Back to Top](#table-of-contents)**
357. ### What happens if we add two arrays
If you add two arrays together, it will convert them both to strings and concatenate them. For example, the result of adding arrays would be as below,
```javascript
console.log(["a"] + ["b"]); // "ab"
console.log([] + []); // ""
console.log(![] + []); // "false", because ![] returns false.
```
**[⬆ Back to Top](#table-of-contents)**
358. ### What is the output of prepend additive operator on falsy values
If you prepend the additive(+) operator on falsy values(null, undefined, NaN, false, ""), the falsy value converts to a number value zero. Let's display them on browser console as below,
```javascript
console.log(+null); // 0
console.log(+undefined); // NaN
console.log(+false); // 0
console.log(+NaN); // NaN
console.log(+""); // 0
```
**[⬆ Back to Top](#table-of-contents)**
359. ### How do you create self string using special characters
The self string can be formed with the combination of `[]()!+` characters. You need to remember the below conventions to achieve this pattern.
1. Since Arrays are truthful values, negating the arrays will produce false: ![] === false
2. As per JavaScript coercion rules, the addition of arrays together will toString them: [] + [] === ""
3. Prepend an array with + operator will convert an array to false, the negation will make it true and finally converting the result will produce value '1': +(!(+[])) === 1
By applying the above rules, we can derive below conditions
```javascript
(![] + [] === "false" + !+[]) === 1;
```
Now the character pattern would be created as below,
```javascript
s e l f
^^^^^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^
(![] + [])[3] + (![] + [])[4] + (![] + [])[2] + (![] + [])[0]
^^^^^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^
(![] + [])[+!+[]+!+[]+!+[]] +
(![] + [])[+!+[]+!+[]+!+[]+!+[]] +
(![] + [])[+!+[]+!+[]] +
(![] + [])[+[]]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(![]+[])[+!+[]+!+[]+!+[]]+(![]+[])[+!+[]+!+[]+!+[]+!+[]]+(![]+[])[+!+[]+!+[]]+(![]+[])[+[]]
```
**[⬆ Back to Top](#table-of-contents)**
360. ### How do you remove falsy values from an array
You can apply the filter method on the array by passing Boolean as a parameter. This way it removes all falsy values(0, undefined, null, false and "") from the array.
```javascript
const myArray = [false, null, 1, 5, undefined];
myArray.filter(Boolean); // [1, 5] // is same as myArray.filter(x => x);
```
**[⬆ Back to Top](#table-of-contents)**
361. ### How do you get unique values of an array
You can get unique values of an array with the combination of `Set` and rest expression/spread(...) syntax.
```javascript
console.log([...new Set([1, 2, 4, 4, 3])]); // [1, 2, 4, 3]
```
**[⬆ Back to Top](#table-of-contents)**
362. ### What is destructuring aliases
Sometimes you would like to have a destructured variable with a different name than the property name. In that case, you'll use a `: newName` to specify a name for the variable. This process is called destructuring aliases.
```javascript
const obj = { x: 1 };
// Grabs obj.x as as { otherName }
const { x: otherName } = obj;
```
**[⬆ Back to Top](#table-of-contents)**
363. ### How do you map the array values without using map method
You can map the array values without using the `map` method by just using the `from` method of Array. Let's map city names from Countries array,
```javascript
const countries = [
{ name: "India", capital: "Delhi" },
{ name: "US", capital: "Washington" },
{ name: "Russia", capital: "Moscow" },
{ name: "Singapore", capital: "Singapore" },
{ name: "China", capital: "Beijing" },
{ name: "France", capital: "Paris" },
];
const cityNames = Array.from(countries, ({ capital }) => capital);
console.log(cityNames); // ['Delhi, 'Washington', 'Moscow', 'Singapore', 'Beijing', 'Paris']
```
**[⬆ Back to Top](#table-of-contents)**
364. ### How do you empty an array
You can empty an array quickly by setting the array length to zero.
```javascript
let cities = ["Singapore", "Delhi", "London"];
cities.length = 0; // cities becomes []
```
**[⬆ Back to Top](#table-of-contents)**
365. ### How do you rounding numbers to certain decimals
You can round numbers to a certain number of decimals using `toFixed` method from native javascript.
```javascript
let pie = 3.141592653;
pie = pie.toFixed(3); // 3.142
```
**[⬆ Back to Top](#table-of-contents)**
366. ### What is the easiest way to convert an array to an object
You can convert an array to an object with the same data using spread(...) operator.
```javascript
var fruits = ["banana", "apple", "orange", "watermelon"];
var fruitsObject = { ...fruits };
console.log(fruitsObject); // {0: "banana", 1: "apple", 2: "orange", 3: "watermelon"}
```
**[⬆ Back to Top](#table-of-contents)**
367. ### How do you create an array with some data
You can create an array with some data or an array with the same values using `fill` method.
```javascript
var newArray = new Array(5).fill("0");
console.log(newArray); // ["0", "0", "0", "0", "0"]
```
**[⬆ Back to Top](#table-of-contents)**
368. ### What are the placeholders from console object
Below are the list of placeholders available from console object,
1. %o — It takes an object,
2. %s — It takes a string,
3. %d — It is used for a decimal or integer
These placeholders can be represented in the console.log as below
```javascript
const user = { name: "John", id: 1, city: "Delhi" };
console.log(
"Hello %s, your details %o are available in the object form",
"John",
user
); // Hello John, your details {name: "John", id: 1, city: "Delhi"} are available in object
```
**[⬆ Back to Top](#table-of-contents)**
369. ### Is it possible to add CSS to console messages
Yes, you can apply CSS styles to console messages similar to html text on the web page.
```javascript
console.log(
"%c The text has blue color, with large font and red background",
"color: blue; font-size: x-large; background: red"
);
```
The text will be displayed as below,
**Note:** All CSS styles can be applied to console messages.
**[⬆ Back to Top](#table-of-contents)**
370. ### What is the purpose of dir method of console object
The `console.dir()` is used to display an interactive list of the properties of the specified JavaScript object as JSON.
```javascript
const user = { name: "John", id: 1, city: "Delhi" };
console.dir(user);
```
The user object displayed in JSON representation
**[⬆ Back to Top](#table-of-contents)**
371. ### Is it possible to debug HTML elements in console
Yes, it is possible to get and debug HTML elements in the console just like inspecting elements.
```javascript
const element = document.getElementsByTagName("body")[0];
console.log(element);
```
It prints the HTML element in the console,
**[⬆ Back to Top](#table-of-contents)**
372. ### How do you display data in a tabular format using console object
The `console.table()` is used to display data in the console in a tabular format to visualize complex arrays or objects.
```js
const users = [
{ name: "John", id: 1, city: "Delhi" },
{ name: "Max", id: 2, city: "London" },
{ name: "Rod", id: 3, city: "Paris" },
];
console.table(users);
```
The data visualized in a table format,
**Not:** Remember that `console.table()` is not supported in IE.
**[⬆ Back to Top](#table-of-contents)**
373. ### How do you verify that an argument is a Number or not
The combination of IsNaN and isFinite methods are used to confirm whether an argument is a number or not.
```javascript
function isNumber(n) {
return !isNaN(parseFloat(n)) && isFinite(n);
}
```
**[⬆ Back to Top](#table-of-contents)**
374. ### How do you create copy to clipboard button
You need to select the content(using .select() method) of the input element and execute the copy command with execCommand (i.e, execCommand('copy')). You can also execute other system commands like cut and paste.
```javascript
document.querySelector("#copy-button").onclick = function () {
// Select the content
document.querySelector("#copy-input").select();
// Copy to the clipboard
document.execCommand("copy");
};
```
**[⬆ Back to Top](#table-of-contents)**
375. ### What is the shortcut to get timestamp
You can use `new Date().getTime()` to get the current timestamp. There is an alternative shortcut to get the value.
```javascript
console.log(+new Date());
console.log(Date.now());
```
**[⬆ Back to Top](#table-of-contents)**
376. ### How do you flattening multi dimensional arrays
Flattening bi-dimensional arrays is trivial with Spread operator.
```javascript
const biDimensionalArr = [11, [22, 33], [44, 55], [66, 77], 88, 99];
const flattenArr = [].concat(...biDimensionalArr); // [11, 22, 33, 44, 55, 66, 77, 88, 99]
```
But you can make it work with multi-dimensional arrays by recursive calls,
```javascript
function flattenMultiArray(arr) {
const flattened = [].concat(...arr);
return flattened.some((item) => Array.isArray(item))
? flattenMultiArray(flattened)
: flattened;
}
const multiDimensionalArr = [11, [22, 33], [44, [55, 66, [77, [88]], 99]]];
const flatArr = flattenMultiArray(multiDimensionalArr); // [11, 22, 33, 44, 55, 66, 77, 88, 99]
```
Also you can use the `flat` method of Array.
```javascript
const arr = [1, [2, 3], 4, 5, [6, 7]];
const fllattenArr = arr.flat(); // [1, 2, 3, 4, 5, 6, 7]
// And for multiDemensional arrays
const multiDimensionalArr = [11, [22, 33], [44, [55, 66, [77, [88]], 99]]];
const oneStepFlat = multiDimensionalArr.flat(1); // [11, 22, 33, 44, [55, 66, [77, [88]], 99]]
const towStep = multiDimensionalArr.flat(2); // [11, 22, 33, 44, 55, 66, [77, [88]], 99]
const fullyFlatArray = multiDimensionalArr.flat(Infinity); // [11, 22, 33, 44, 55, 66, 77, 88, 99]
```
**[⬆ Back to Top](#table-of-contents)**
377. ### What is the easiest multi condition checking
You can use `indexOf` to compare input with multiple values instead of checking each value as one condition.
```javascript
// Verbose approach
if (
input === "first" ||
input === 1 ||
input === "second" ||
input === 2
) {
someFunction();
}
// Shortcut
if (["first", 1, "second", 2].indexOf(input) !== -1) {
someFunction();
}
```
**[⬆ Back to Top](#table-of-contents)**
378. ### How do you capture browser back button
The `beforeunload` event is triggered when the window, the document and its resources are about to be unloaded. This event is helpful to warn users about losing the current data and detect back button event.
```javascript
window.addEventListener('beforeunload', () => {
console.log('Clicked browser back button');
});
```
You can also use `popstate` event to detect the browser back button.
**Note:** The history entry has been activated using `history.pushState` method.
```javascript
window.addEventListener('popstate', () => {
console.log('Clicked browser back button');
box.style.backgroundColor = 'white';
});
const box = document.getElementById('div');
box.addEventListener('click', () => {
box.style.backgroundColor = 'blue';
window.history.pushState({}, null, null);
});
```
In the preceeding code, When the box element clicked, its background color appears in blue color and changed to while color upon clicking the browser back button using `popstate` event handler. The `state` property of `popstate` contains the copy of history entry's state object.
**[⬆ Back to Top](#table-of-contents)**
379. ### How do you disable right click in the web page
The right click on the page can be disabled by returning false from the `oncontextmenu` attribute on the body element.
```html
<body oncontextmenu="return false;"></body>
```
**[⬆ Back to Top](#table-of-contents)**
380. ### What are wrapper objects
Primitive Values like string,number and boolean don't have properties and methods but they are temporarily converted or coerced to an object(Wrapper object) when you try to perform actions on them. For example, if you apply toUpperCase() method on a primitive string value, it does not throw an error but returns uppercase of the string.
```javascript
let name = "john";
console.log(name.toUpperCase()); // Behind the scenes treated as console.log(new String(name).toUpperCase());
```
i.e, Every primitive except null and undefined have Wrapper Objects and the list of wrapper objects are String,Number,Boolean,Symbol and BigInt.
**[⬆ Back to Top](#table-of-contents)**
381. ### What is AJAX
AJAX stands for Asynchronous JavaScript and XML and it is a group of related technologies(HTML, CSS, JavaScript, XMLHttpRequest API etc) used to display data asynchronously. i.e. We can send data to the server and get data from the server without reloading the web page.
**[⬆ Back to Top](#table-of-contents)**
382. ### What are the different ways to deal with Asynchronous Code
Below are the list of different ways to deal with Asynchronous code.
1. Callbacks
2. Promises
3. Async/await
4. Third-party libraries such as async.js,bluebird etc
**[⬆ Back to Top](#table-of-contents)**
383. ### How to cancel a fetch request
Until a few days back, One shortcoming of native promises is no direct way to cancel a fetch request. But the new `AbortController` from js specification allows you to use a signal to abort one or multiple fetch calls.
The basic flow of cancelling a fetch request would be as below,
1. Create an `AbortController` instance
2. Get the signal property of an instance and pass the signal as a fetch option for signal
3. Call the AbortController's abort property to cancel all fetches that use that signal
For example, let's pass the same signal to multiple fetch calls will cancel all requests with that signal,
```javascript
const controller = new AbortController();
const { signal } = controller;
fetch("http://localhost:8000", { signal })
.then((response) => {
console.log(`Request 1 is complete!`);
})
.catch((e) => {
if (e.name === "AbortError") {
// We know it's been canceled!
}
});
fetch("http://localhost:8000", { signal })
.then((response) => {
console.log(`Request 2 is complete!`);
})
.catch((e) => {
if (e.name === "AbortError") {
// We know it's been canceled!
}
});
// Wait 2 seconds to abort both requests
setTimeout(() => controller.abort(), 2000);
```
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384. ### What is web speech API
Web speech API is used to enable modern browsers recognize and synthesize speech(i.e, voice data into web apps). This API has been introduced by W3C Community in the year 2012. It has two main parts,
1. **SpeechRecognition (Asynchronous Speech Recognition or Speech-to-Text):** It provides the ability to recognize voice context from an audio input and respond accordingly. This is accessed by the `SpeechRecognition` interface.
The below example shows on how to use this API to get text from speech,
```javascript
window.SpeechRecognition =
window.webkitSpeechRecognition || window.SpeechRecognition; // webkitSpeechRecognition for Chrome and SpeechRecognition for FF
const recognition = new window.SpeechRecognition();
recognition.onresult = (event) => {
// SpeechRecognitionEvent type
const speechToText = event.results[0][0].transcript;
console.log(speechToText);
};
recognition.start();
```
In this API, browser is going to ask you for permission to use your microphone
1. **SpeechSynthesis (Text-to-Speech):** It provides the ability to recognize voice context from an audio input and respond. This is accessed by the `SpeechSynthesis` interface.
For example, the below code is used to get voice/speech from text,
```javascript
if ("speechSynthesis" in window) {
var speech = new SpeechSynthesisUtterance("Hello World!");
speech.lang = "en-US";
window.speechSynthesis.speak(speech);
}
```
The above examples can be tested on chrome(33+) browser's developer console.
**Note:** This API is still a working draft and only available in Chrome and Firefox browsers(ofcourse Chrome only implemented the specification)
**[⬆ Back to Top](#table-of-contents)**
385. ### What is minimum timeout throttling
Both browser and NodeJS javascript environments throttles with a minimum delay that is greater than 0ms. That means even though setting a delay of 0ms will not happen instantaneously.
**Browsers:** They have a minimum delay of 4ms. This throttle occurs when successive calls are triggered due to callback nesting(certain depth) or after a certain number of successive intervals.
Note: The older browsers have a minimum delay of 10ms.
**Nodejs:** They have a minimum delay of 1ms. This throttle happens when the delay is larger than 2147483647 or less than 1.
The best example to explain this timeout throttling behavior is the order of below code snippet.
```javascript
function runMeFirst() {
console.log("My script is initialized");
}
setTimeout(runMeFirst, 0);
console.log("Script loaded");
```
and the output would be in
```cmd
Script loaded
My script is initialized
```
If you don't use `setTimeout`, the order of logs will be sequential.
```javascript
function runMeFirst() {
console.log("My script is initialized");
}
runMeFirst();
console.log("Script loaded");
```
and the output is,
```cmd
My script is initialized
Script loaded
```
**[⬆ Back to Top](#table-of-contents)**
386. ### How do you implement zero timeout in modern browsers
You can't use setTimeout(fn, 0) to execute the code immediately due to minimum delay of greater than 0ms. But you can use window.postMessage() to achieve this behavior.
**[⬆ Back to Top](#table-of-contents)**
387. ### What are tasks in event loop
A task is any javascript code/program which is scheduled to be run by the standard mechanisms such as initially starting to run a program, run an event callback, or an interval or timeout being fired. All these tasks are scheduled on a task queue.
Below are the list of use cases to add tasks to the task queue,
1. When a new javascript program is executed directly from console or running by the `<script>` element, the task will be added to the task queue.
2. When an event fires, the event callback added to task queue
3. When a setTimeout or setInterval is reached, the corresponding callback added to task queue
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388. ### What is microtask
Microtask is the javascript code which needs to be executed immediately after the currently executing task/microtask is completed. They are kind of blocking in nature. i.e, The main thread will be blocked until the microtask queue is empty.
The main sources of microtasks are Promise.resolve, Promise.reject, MutationObservers, IntersectionObservers etc
**Note:** All of these microtasks are processed in the same turn of the event loop.
**[⬆ Back to Top](#table-of-contents)**
389. ### What are different event loops
In JavaScript, there are multiple event loops that can be used depending on the context of your application. The most common event loops are:
1. The Browser Event Loop
2. The Node.js Event Loop
- Browser Event Loop: The Browser Event Loop is used in client-side JavaScript applications and is responsible for handling events that occur within the browser environment, such as user interactions (clicks, keypresses, etc.), HTTP requests, and other asynchronous actions.
- The Node.js Event Loop is used in server-side JavaScript applications and is responsible for handling events that occur within the Node.js runtime environment, such as file I/O, network I/O, and other asynchronous actions.
**[⬆ Back to Top](#table-of-contents)**
390. ### What is the purpose of queueMicrotask
The `queueMicrotask` function is used to schedule a microtask, which is a function that will be executed asynchronously in the microtask queue. The purpose of `queueMicrotask` is to ensure that a function is executed after the current task has finished, but before the browser performs any rendering or handles user events.
Example:
```javascript
console.log("Start"); //1
queueMicrotask(() => {
console.log("Inside microtask"); // 3
});
console.log("End"); //2
```
By using queueMicrotask, you can ensure that certain tasks or callbacks are executed at the earliest opportunity during the JavaScript event loop, making it useful for performing work that needs to be done asynchronously but with higher priority than regular `setTimeout` or `setInterval` callbacks.
**[⬆ Back to Top](#table-of-contents)**
391. ### How do you use javascript libraries in typescript file
It is known that not all JavaScript libraries or frameworks have TypeScript declaration files. But if you still want to use libraries or frameworks in our TypeScript files without getting compilation errors, the only solution is `declare` keyword along with a variable declaration. For example, let's imagine you have a library called `customLibrary` that doesn’t have a TypeScript declaration and have a namespace called `customLibrary` in the global namespace. You can use this library in typescript code as below,
```javascript
declare var customLibrary;
```
In the runtime, typescript will provide the type to the `customLibrary` variable as `any` type. The another alternative without using declare keyword is below
```javascript
var customLibrary: any;
```
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392. ### What are the differences between promises and observables
Some of the major difference in a tabular form
| Promises | Observables |
| ------------------------------------------------------------------ | ---------------------------------------------------------------------------------------- |
| Emits only a single value at a time | Emits multiple values over a period of time(stream of values ranging from 0 to multiple) |
| Eager in nature; they are going to be called immediately | Lazy in nature; they require subscription to be invoked |
| Promise is always asynchronous even though it resolved immediately | Observable can be either synchronous or asynchronous |
| Doesn't provide any operators | Provides operators such as map, forEach, filter, reduce, retry, and retryWhen etc |
| Cannot be canceled | Canceled by using unsubscribe() method |
**[⬆ Back to Top](#table-of-contents)**
393. ### What is heap
Heap(Or memory heap) is the memory location where objects are stored when we define variables. i.e, This is the place where all the memory allocations and de-allocation take place. Both heap and call-stack are two containers of JS runtime.
Whenever runtime comes across variables and function declarations in the code it stores them in the Heap.
**[⬆ Back to Top](#table-of-contents)**
394. ### What is an event table
Event Table is a data structure that stores and keeps track of all the events which will be executed asynchronously like after some time interval or after the resolution of some API requests. i.e Whenever you call a setTimeout function or invoke async operation, it is added to the Event Table.
It doesn't not execute functions on it’s own. The main purpose of the event table is to keep track of events and send them to the Event Queue as shown in the below diagram.
**[⬆ Back to Top](#table-of-contents)**
395. ### What is a microTask queue
Microtask Queue is the new queue where all the tasks initiated by promise objects get processed before the callback queue.
The microtasks queue are processed before the next rendering and painting jobs. But if these microtasks are running for a long time then it leads to visual degradation.
**[⬆ Back to Top](#table-of-contents)**
396. ### What is the difference between shim and polyfill
A shim is a library that brings a new API to an older environment, using only the means of that environment. It isn't necessarily restricted to a web application. For example, es5-shim.js is used to emulate ES5 features on older browsers (mainly pre IE9).
Whereas polyfill is a piece of code (or plugin) that provides the technology that you, the developer, expect the browser to provide natively.
In a simple sentence, A polyfill is a shim for a browser API.
**[⬆ Back to Top](#table-of-contents)**
397. ### How do you detect primitive or non primitive value type
In JavaScript, primitive types include boolean, string, number, BigInt, null, Symbol and undefined. Whereas non-primitive types include the Objects. But you can easily identify them with the below function,
```javascript
var myPrimitive = 30;
var myNonPrimitive = {};
function isPrimitive(val) {
return Object(val) !== val;
}
isPrimitive(myPrimitive);
isPrimitive(myNonPrimitive);
```
If the value is a primitive data type, the Object constructor creates a new wrapper object for the value. But If the value is a non-primitive data type (an object), the Object constructor will give the same object.
**[⬆ Back to Top](#table-of-contents)**
398. ### What is babel
Babel is a JavaScript transpiler to convert ECMAScript 2015+ code into a backwards compatible version of JavaScript in current and older browsers or environments. Some of the main features are listed below,
1. Transform syntax
2. Polyfill features that are missing in your target environment (using @babel/polyfill)
3. Source code transformations (or codemods)
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399. ### Is Node.js completely single threaded
Node is a single thread, but some of the functions included in the Node.js standard library(e.g, fs module functions) are not single threaded. i.e, Their logic runs outside of the Node.js single thread to improve the speed and performance of a program.
**[⬆ Back to Top](#table-of-contents)**
400. ### What are the common use cases of observables
Some of the most common use cases of observables are web sockets with push notifications, user input changes, repeating intervals, etc
**[⬆ Back to Top](#table-of-contents)**
401. ### What is RxJS
RxJS (Reactive Extensions for JavaScript) is a library for implementing reactive programming using observables that makes it easier to compose asynchronous or callback-based code. It also provides utility functions for creating and working with observables.
**[⬆ Back to Top](#table-of-contents)**
402. ### What is the difference between Function constructor and function declaration
The functions which are created with `Function constructor` do not create closures to their creation contexts but they are always created in the global scope. i.e, the function can access its own local variables and global scope variables only. Whereas function declarations can access outer function variables(closures) too.
Let's see this difference with an example,
**Function Constructor:**
```javascript
var a = 100;
function createFunction() {
var a = 200;
return new Function("return a;");
}
console.log(createFunction()()); // 100
```
**Function declaration:**
```javascript
var a = 100;
function createFunction() {
var a = 200;
return function func() {
return a;
};
}
console.log(createFunction()()); // 200
```
**[⬆ Back to Top](#table-of-contents)**
403. ### What is a Short circuit condition
Short circuit conditions are meant for condensed way of writing simple if statements. Let's demonstrate the scenario using an example. If you would like to login to a portal with an authentication condition, the expression would be as below,
```javascript
if (authenticate) {
loginToPorta();
}
```
Since the javascript logical operators evaluated from left to right, the above expression can be simplified using && logical operator
```javascript
authenticate && loginToPorta();
```
**[⬆ Back to Top](#table-of-contents)**
404. ### What is the easiest way to resize an array
The length property of an array is useful to resize or empty an array quickly. Let's apply length property on number array to resize the number of elements from 5 to 2,
```javascript
var array = [1, 2, 3, 4, 5];
console.log(array.length); // 5
array.length = 2;
console.log(array.length); // 2
console.log(array); // [1,2]
```
and the array can be emptied too
```javascript
var array = [1, 2, 3, 4, 5];
array.length = 0;
console.log(array.length); // 0
console.log(array); // []
```
**[⬆ Back to Top](#table-of-contents)**
405. ### What is an observable
An Observable is basically a function that can return a stream of values either synchronously or asynchronously to an observer over time. The consumer can get the value by calling `subscribe()` method.
Let's look at a simple example of an Observable
```javascript
import { Observable } from "rxjs";
const observable = new Observable((observer) => {
setTimeout(() => {
observer.next("Message from a Observable!");
}, 3000);
});
observable.subscribe((value) => console.log(value));
```
**Note:** Observables are not part of the JavaScript language yet but they are being proposed to be added to the language
**[⬆ Back to Top](#table-of-contents)**
406. ### What is the difference between function and class declarations
The main difference between function declarations and class declarations is `hoisting`. The function declarations are hoisted but not class declarations.
**Classes:**
```javascript
const user = new User(); // ReferenceError
class User {}
```
**Constructor Function:**
```javascript
const user = new User(); // No error
function User() {}
```
**[⬆ Back to Top](#table-of-contents)**
407. ### What is an async function
An async function is a function declared with the `async` keyword which enables asynchronous, promise-based behavior to be written in a cleaner style by avoiding promise chains. These functions can contain zero or more `await` expressions.
Let's take a below async function example,
```javascript
async function logger() {
let data = await fetch("http://someapi.com/users"); // pause until fetch returns
console.log(data);
}
logger();
```
It is basically syntax sugar over ES2015 promises and generators.
**[⬆ Back to Top](#table-of-contents)**
408. ### How do you prevent promises swallowing errors
While using asynchronous code, JavaScript’s ES6 promises can make your life a lot easier without having callback pyramids and error handling on every second line. But Promises have some pitfalls and the biggest one is swallowing errors by default.
Let's say you expect to print an error to the console for all the below cases,
```javascript
Promise.resolve("promised value").then(function () {
throw new Error("error");
});
Promise.reject("error value").catch(function () {
throw new Error("error");
});
new Promise(function (resolve, reject) {
throw new Error("error");
});
```
But there are many modern JavaScript environments that won't print any errors. You can fix this problem in different ways,
1. **Add catch block at the end of each chain:** You can add catch block to the end of each of your promise chains
```javascript
Promise.resolve("promised value")
.then(function () {
throw new Error("error");
})
.catch(function (error) {
console.error(error.stack);
});
```
But it is quite difficult to type for each promise chain and verbose too.
2. **Add done method:** You can replace first solution's then and catch blocks with done method
```javascript
Promise.resolve("promised value").done(function () {
throw new Error("error");
});
```
Let's say you want to fetch data using HTTP and later perform processing on the resulting data asynchronously. You can write `done` block as below,
```javascript
getDataFromHttp()
.then(function (result) {
return processDataAsync(result);
})
.done(function (processed) {
displayData(processed);
});
```
In future, if the processing library API changed to synchronous then you can remove `done` block as below,
```javascript
getDataFromHttp().then(function (result) {
return displayData(processDataAsync(result));
});
```
and then you forgot to add `done` block to `then` block leads to silent errors.
3. **Extend ES6 Promises by Bluebird:**
Bluebird extends the ES6 Promises API to avoid the issue in the second solution. This library has a “default” onRejection handler which will print all errors from rejected Promises to stderr. After installation, you can process unhandled rejections
```javascript
Promise.onPossiblyUnhandledRejection(function (error) {
throw error;
});
```
and discard a rejection, just handle it with an empty catch
```javascript
Promise.reject("error value").catch(function () {});
```
**[⬆ Back to Top](#table-of-contents)**
409. ### What is deno
Deno is a simple, modern and secure runtime for JavaScript and TypeScript that uses V8 JavaScript engine and the Rust programming language.
**[⬆ Back to Top](#table-of-contents)**
410. ### How do you make an object iterable in javascript
By default, plain objects are not iterable. But you can make the object iterable by defining a `Symbol.iterator` property on it.
Let's demonstrate this with an example,
```javascript
const collection = {
one: 1,
two: 2,
three: 3,
[Symbol.iterator]() {
const values = Object.keys(this);
let i = 0;
return {
next: () => {
return {
value: this[values[i++]],
done: i > values.length,
};
},
};
},
};
const iterator = collection[Symbol.iterator]();
console.log(iterator.next()); // → {value: 1, done: false}
console.log(iterator.next()); // → {value: 2, done: false}
console.log(iterator.next()); // → {value: 3, done: false}
console.log(iterator.next()); // → {value: undefined, done: true}
```
The above process can be simplified using a generator function,
```javascript
const collection = {
one: 1,
two: 2,
three: 3,
[Symbol.iterator]: function* () {
for (let key in this) {
yield this[key];
}
},
};
const iterator = collection[Symbol.iterator]();
console.log(iterator.next()); // {value: 1, done: false}
console.log(iterator.next()); // {value: 2, done: false}
console.log(iterator.next()); // {value: 3, done: false}
console.log(iterator.next()); // {value: undefined, done: true}
```
**[⬆ Back to Top](#table-of-contents)**
411. ### What is a Proper Tail Call
First, we should know about tail call before talking about "Proper Tail Call". A tail call is a subroutine or function call performed as the final action of a calling function. Whereas **Proper tail call(PTC)** is a technique where the program or code will not create additional stack frames for a recursion when the function call is a tail call.
For example, the below classic or head recursion of factorial function relies on stack for each step. Each step need to be processed upto `n * factorial(n - 1)`
```javascript
function factorial(n) {
if (n === 0) {
return 1;
}
return n * factorial(n - 1);
}
console.log(factorial(5)); //120
```
But if you use Tail recursion functions, they keep passing all the necessary data it needs down the recursion without relying on the stack.
```javascript
function factorial(n, acc = 1) {
if (n === 0) {
return acc;
}
return factorial(n - 1, n * acc);
}
console.log(factorial(5)); //120
```
The above pattern returns the same output as the first one. But the accumulator keeps track of total as an argument without using stack memory on recursive calls.
**[⬆ Back to Top](#table-of-contents)**
412. ### How do you check an object is a promise or not
If you don't know if a value is a promise or not, wrapping the value as `Promise.resolve(value)` which returns a promise
```javascript
function isPromise(object) {
if (Promise && Promise.resolve) {
return Promise.resolve(object) == object;
} else {
throw "Promise not supported in your environment";
}
}
var i = 1;
var promise = new Promise(function (resolve, reject) {
resolve();
});
console.log(isPromise(i)); // false
console.log(isPromise(promise)); // true
```
Another way is to check for `.then()` handler type
```javascript
function isPromise(value) {
return Boolean(value && typeof value.then === "function");
}
var i = 1;
var promise = new Promise(function (resolve, reject) {
resolve();
});
console.log(isPromise(i)); // false
console.log(isPromise(promise)); // true
```
**[⬆ Back to Top](#table-of-contents)**
413. ### How to detect if a function is called as constructor
You can use `new.target` pseudo-property to detect whether a function was called as a constructor(using the new operator) or as a regular function call.
1. If a constructor or function invoked using the new operator, new.target returns a reference to the constructor or function.
2. For function calls, new.target is undefined.
```javascript
function Myfunc() {
if (new.target) {
console.log("called with new");
} else {
console.log("not called with new");
}
}
new Myfunc(); // called with new
Myfunc(); // not called with new
Myfunc.call({}); // not called with new
```
**[⬆ Back to Top](#table-of-contents)**
414. ### What are the differences between arguments object and rest parameter
There are three main differences between arguments object and rest parameters
1. The arguments object is an array-like but not an array. Whereas the rest parameters are array instances.
2. The arguments object does not support methods such as sort, map, forEach, or pop. Whereas these methods can be used in rest parameters.
3. The rest parameters are only the ones that haven’t been given a separate name, while the arguments object contains all arguments passed to the function
**[⬆ Back to Top](#table-of-contents)**
415. ### What are the differences between spread operator and rest parameter
Rest parameter collects all remaining elements into an array. Whereas Spread operator allows iterables( arrays / objects / strings ) to be expanded into single arguments/elements. i.e, Rest parameter is opposite to the spread operator.
**[⬆ Back to Top](#table-of-contents)**
416. ### What are the different kinds of generators
There are five kinds of generators,
1. **Generator function declaration:**
```javascript
function* myGenFunc() {
yield 1;
yield 2;
yield 3;
}
const genObj = myGenFunc();
```
2. **Generator function expressions:**
```javascript
const myGenFunc = function* () {
yield 1;
yield 2;
yield 3;
};
const genObj = myGenFunc();
```
3. **Generator method definitions in object literals:**
```javascript
const myObj = {
*myGeneratorMethod() {
yield 1;
yield 2;
yield 3;
},
};
const genObj = myObj.myGeneratorMethod();
```
4. **Generator method definitions in class:**
```javascript
class MyClass {
*myGeneratorMethod() {
yield 1;
yield 2;
yield 3;
}
}
const myObject = new MyClass();
const genObj = myObject.myGeneratorMethod();
```
5. **Generator as a computed property:**
```javascript
const SomeObj = {
*[Symbol.iterator]() {
yield 1;
yield 2;
yield 3;
},
};
console.log(Array.from(SomeObj)); // [ 1, 2, 3 ]
```
**[⬆ Back to Top](#table-of-contents)**
417. ### What are the built-in iterables
Below are the list of built-in iterables in javascript,
1. Arrays and TypedArrays
2. Strings: Iterate over each character or Unicode code-points
3. Maps: iterate over its key-value pairs
4. Sets: iterates over their elements
5. arguments: An array-like special variable in functions
6. DOM collection such as NodeList
**[⬆ Back to Top](#table-of-contents)**
418. ### What are the differences between for...of and for...in statements
Both for...in and for...of statements iterate over js data structures. The only difference is over what they iterate:
1. for..in iterates over all enumerable property keys of an object
2. for..of iterates over the values of an iterable object.
Let's explain this difference with an example,
```javascript
let arr = ["a", "b", "c"];
arr.newProp = "newVlue";
// key are the property keys
for (let key in arr) {
console.log(key); // 0, 1, 2 & newValue
}
// value are the property values
for (let value of arr) {
console.log(value); // a, b, c
}
```
Since for..in loop iterates over the keys of the object, the first loop logs 0, 1, 2 and newProp while iterating over the array object. The for..of loop iterates over the values of a arr data structure and logs a, b, c in the console.
**[⬆ Back to Top](#table-of-contents)**
419. ### How do you define instance and non-instance properties
The Instance properties must be defined inside of class methods. For example, name and age properties defined inside constructor as below,
```javascript
class Person {
constructor(name, age) {
this.name = name;
this.age = age;
}
}
```
But Static(class) and prototype data properties must be defined outside of the ClassBody declaration. Let's assign the age value for Person class as below,
```javascript
Person.staticAge = 30;
Person.prototype.prototypeAge = 40;
```
**[⬆ Back to Top](#table-of-contents)**
420. ### What is the difference between isNaN and Number.isNaN?
1. **isNaN**: The global function `isNaN` converts the argument to a Number and returns true if the resulting value is NaN.
2. **Number.isNaN**: This method does not convert the argument. But it returns true when the type is a Number and value is NaN.
Let's see the difference with an example,
```javascript
isNaN(‘hello’); // true
Number.isNaN('hello'); // false
```
**[⬆ Back to Top](#table-of-contents)**
421. ### How to invoke an IIFE without any extra brackets?
Immediately Invoked Function Expressions(IIFE) requires a pair of parenthesis to wrap the function which contains set of statements.
```js
(function (dt) {
console.log(dt.toLocaleTimeString());
})(new Date());
```
Since both IIFE and void operator discard the result of an expression, you can avoid the extra brackets using `void operator` for IIFE as below,
```js
void (function (dt) {
console.log(dt.toLocaleTimeString());
})(new Date());
```
**[⬆ Back to Top](#table-of-contents)**
422. ### Is that possible to use expressions in switch cases?
You might have seen expressions used in switch condition but it is also possible to use for switch cases by assigning true value for the switch condition. Let's see the weather condition based on temparature as an example,
```js
const weather = (function getWeather(temp) {
switch (true) {
case temp < 0:
return "freezing";
case temp < 10:
return "cold";
case temp < 24:
return "cool";
default:
return "unknown";
}
})(10);
```
**[⬆ Back to Top](#table-of-contents)**
423. ### What is the easiest way to ignore promise errors?
The easiest and safest way to ignore promise errors is void that error. This approach is ESLint friendly too.
```js
await promise.catch((e) => void e);
```
**[⬆ Back to Top](#table-of-contents)**
424. ### How do style the console output using CSS?
You can add CSS styling to the console output using the CSS format content specifier %c. The console string message can be appended after the specifier and CSS style in another argument. Let's print the red the color text using console.log and CSS specifier as below,
```js
console.log("%cThis is a red text", "color:red");
```
It is also possible to add more styles for the content. For example, the font-size can be modified for the above text
```js
console.log(
"%cThis is a red text with bigger font",
"color:red; font-size:20px"
);
```
**[⬆ Back to Top](#table-of-contents)**
425. ### What is nullish coalescing operator (??)?
It is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand. This can be contrasted with the logical OR (||) operator, which returns the right-hand side operand if the left operand is any falsy value, not only null or undefined.
```js
console.log(null ?? true); // true
console.log(false ?? true); // false
console.log(undefined ?? true); // true
```
**[⬆ Back to Top](#table-of-contents)**
426. ### How do you group and nest console output?
The `console.group()` can be used to group related log messages to be able to easily read the logs and use console.groupEnd()to close the group. Along with this, you can also nest groups which allows to output message in hierarchical manner.
For example, if you’re logging a user’s details:
```js
console.group("User Details");
console.log("name: Sudheer Jonna");
console.log("job: Software Developer");
// Nested Group
console.group("Address");
console.log("Street: Commonwealth");
console.log("City: Los Angeles");
console.log("State: California");
// Close nested group
console.groupEnd();
// Close outer group
console.groupEnd();
```
You can also use `console.groupCollapsed()` instead of `console.group()` if you want the groups to be collapsed by default.
**[⬆ Back to Top](#table-of-contents)**
427. ### What is the difference between dense and sparse arrays?
An array contains items at each index starting from first(0) to last(array.length - 1) is called as Dense array. Whereas if at least one item is missing at any index, the array is called as sparse.
Let's see the below two kind of arrays,
```js
const avengers = ["Ironman", "Hulk", "CaptainAmerica"];
console.log(avengers[0]); // 'Ironman'
console.log(avengers[1]); // 'Hulk'
console.log(avengers[2]); // 'CaptainAmerica'
console.log(avengers.length); // 3
const justiceLeague = ["Superman", "Aquaman", , "Batman"];
console.log(justiceLeague[0]); // 'Superman'
console.log(justiceLeague[1]); // 'Aquaman'
console.log(justiceLeague[2]); // undefined
console.log(justiceLeague[3]); // 'Batman'
console.log(justiceLeague.length); // 4
```
**[⬆ Back to Top](#table-of-contents)**
428. ### What are the different ways to create sparse arrays?
There are 4 different ways to create sparse arrays in JavaScript
1. **Array literal:** Omit a value when using the array literal
```js
const justiceLeague = ["Superman", "Aquaman", , "Batman"];
console.log(justiceLeague); // ['Superman', 'Aquaman', empty ,'Batman']
```
2. **Array() constructor:** Invoking Array(length) or new Array(length)
```js
const array = Array(3);
console.log(array); // [empty, empty ,empty]
```
3. **Delete operator:** Using delete array[index] operator on the array
```js
const justiceLeague = ["Superman", "Aquaman", "Batman"];
delete justiceLeague[1];
console.log(justiceLeague); // ['Superman', empty, ,'Batman']
```
4. **Increase length property:** Increasing length property of an array
```js
const justiceLeague = ["Superman", "Aquaman", "Batman"];
justiceLeague.length = 5;
console.log(justiceLeague); // ['Superman', 'Aquaman', 'Batman', empty, empty]
```
**[⬆ Back to Top](#table-of-contents)**
429. ### What is the difference between setTimeout, setImmediate and process.nextTick?
1. **Set Timeout:** setTimeout() is to schedule execution of a one-time callback after delay milliseconds.
2. **Set Immediate:** The setImmediate function is used to execute a function right after the current event loop finishes.
3. **Process NextTick:** If process.nextTick() is called in a given phase, all the callbacks passed to process.nextTick() will be resolved before the event loop continues. This will block the event loop and create I/O Starvation if process.nextTick() is called recursively.
**[⬆ Back to Top](#table-of-contents)**
430. ### How do you reverse an array without modifying original array?
The `reverse()` method reverses the order of the elements in an array but it mutates the original array. Let's take a simple example to demonistrate this case,
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.reverse();
console.log(newArray); // [ 5, 4, 3, 2, 1]
console.log(originalArray); // [ 5, 4, 3, 2, 1]
```
There are few solutions that won't mutate the original array. Let's take a look.
1. **Using slice and reverse methods:**
In this case, just invoke the `slice()` method on the array to create a shallow copy followed by `reverse()` method call on the copy.
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.slice().reverse(); //Slice an array gives a new copy
console.log(originalArray); // [1, 2, 3, 4, 5]
console.log(newArray); // [ 5, 4, 3, 2, 1]
```
2. **Using spread and reverse methods:**
In this case, let's use the spread syntax (...) to create a copy of the array followed by `reverse()` method call on the copy.
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = [...originalArray].reverse();
console.log(originalArray); // [1, 2, 3, 4, 5]
console.log(newArray); // [ 5, 4, 3, 2, 1]
```
3. **Using reduce and spread methods:**
Here execute a reducer function on an array elements and append the accumulated array on right side using spread syntax
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.reduce((accumulator, value) => {
return [value, ...accumulator];
}, []);
console.log(originalArray); // [1, 2, 3, 4, 5]
console.log(newArray); // [ 5, 4, 3, 2, 1]
```
4. **Using reduceRight and spread methods:**
Here execute a right reducer function(i.e. opposite direction of reduce method) on an array elements and append the accumulated array on left side using spread syntax
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.reduceRight((accumulator, value) => {
return [...accumulator, value];
}, []);
console.log(originalArray); // [1, 2, 3, 4, 5]
console.log(newArray); // [ 5, 4, 3, 2, 1]
```
5. **Using reduceRight and push methods:**
Here execute a right reducer function(i.e. opposite direction of reduce method) on an array elements and push the iterated value to the accumulator
```javascript
const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.reduceRight((accumulator, value) => {
accumulator.push(value);
return accumulator;
}, []);
console.log(originalArray); // [1, 2, 3, 4, 5]
console.log(newArray); // [ 5, 4, 3, 2, 1]
```
**[⬆ Back to Top](#table-of-contents)**
431. ### How do you create custom HTML element?
The creation of custom HTML elements involves two main steps,
1. **Define your custom HTML element:** First you need to define some custom class by extending HTMLElement class.
After that define your component properties (styles,text etc) using `connectedCallback` method.
**Note:** The browser exposes a function called `customElements.define` inorder to reuse the element.
```javascript
class CustomElement extends HTMLElement {
connectedCallback() {
this.innerHTML = "This is a custom element";
}
}
customElements.define("custom-element", CustomElement);
```
2. **Use custome element just like other HTML element:** Declare your custom element as a HTML tag.
```javascript
<body>
<custom-element>
</body>
```
**[⬆ Back to Top](#table-of-contents)**
432. ### What is global execution context?
The global execution context is the default or first execution context that is created by the JavaScript engine before any code is executed(i.e, when the file first loads in the browser). All the global code that is not inside a function or object will be executed inside this global execution context. Since JS engine is single threaded there will be only one global environment and there will be only one global execution context.
For example, the below code other than code inside any function or object is executed inside the global execution context.
```javascript
var x = 10;
function A() {
console.log("Start function A");
function B() {
console.log("In function B");
}
B();
}
A();
console.log("GlobalContext");
```
**[⬆ Back to Top](#table-of-contents)**
433. ### What is function execution context?
Whenever a function is invoked, the JavaScript engine creates a different type of Execution Context known as a Function Execution Context (FEC) within the Global Execution Context (GEC) to evaluate and execute the code within that function.
**[⬆ Back to Top](#table-of-contents)**
434. ### What is debouncing?
Debouncing is a programming pattern that allows delaying execution of some piece of code until a specified time to avoid unnecessary _CPU cycles, API calls and improve performance_. The debounce function make sure that your code is only triggered once per user input. The common usecases are Search box suggestions, text-field auto-saves, and eliminating double-button clicks.
Let's say you want to show suggestions for a search query, but only after a visitor has finished typing it. So here you write a debounce function where the user keeps writing the characters with in 500ms then previous timer cleared out using `clearTimeout` and reschedule API call/DB query for a new time—300 ms in the future.
```js
function debounce(func, timeout = 500) {
let timer;
return (...args) => {
clearTimeout(timer);
timer = setTimeout(() => {
func.apply(this, args);
}, timeout);
};
}
function fetchResults() {
console.log("Fetching input suggestions");
}
const processChange = debounce(() => fetchResults());
```
The _debounce()_ function can be used on input, button and window events
**Input:**
```html
<input type="text" onkeyup="processChange()" />
```
**Button:**
```html
<button onclick="processChange()">Click me</button>
```
**Windows event:**
```html
window.addEventListener("scroll", processChange);
```
**[⬆ Back to Top](#table-of-contents)**
435. ### What is throttling?
Throttling is a technique used to limit the execution of an event handler function, even when this event triggers continuously due to user actions. The common use cases are browser resizing, window scrolling etc.
The below example creates a throttle function to reduce the number of events for each pixel change and trigger scroll event for each 100ms except for the first event.
```js
const throttle = (func, limit) => {
let inThrottle;
return (...args) => {
if (!inThrottle) {
func.apply(this, args);
inThrottle = true;
setTimeout(() => (inThrottle = false), limit);
}
};
};
window.addEventListener("scroll", () => {
throttle(handleScrollAnimation, 100);
});
```
**[⬆ Back to Top](#table-of-contents)**
436. ### What is optional chaining?
According to MDN official docs, the optional chaining operator (?.) permits reading the value of a property located deep within a chain of connected objects without having to expressly validate that each reference in the chain is valid.
The ?. operator is like the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined. When used with function calls, it returns undefined if the given function does not exist.
```js
const adventurer = {
name: "Alice",
cat: {
name: "Dinah",
},
};
const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined
console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined
```
**[⬆ Back to Top](#table-of-contents)**
437. ### What is an environment record?
According to ECMAScript specification 262 (9.1):
> [Environment Record](https://262.ecma-international.org/12.0/#sec-environment-records) is a specification type used to define the association of Identifiers to specific variables and functions, based upon the lexical nesting structure of ECMAScript code.
Usually an Environment Record is associated with some specific syntactic structure of ECMAScript code such as a FunctionDeclaration, a BlockStatement, or a Catch clause of a TryStatement.
Each time such code is evaluated, a new Environment Record is created to record the identifier bindings that are created by that code.
**[⬆ Back to Top](#table-of-contents)**
438. ### How to verify if a variable is an array?
It is possible to check if a variable is an array instance using 3 different ways,
1. Array.isArray() method:
The `Array.isArray(value)` utility function is used to determine whether value is an array or not. This function returns a true boolean value if the variable is an array and a false value if it is not.
```javascript
const numbers = [1, 2, 3];
const user = { name: "John" };
Array.isArray(numbers); // true
Array.isArray(user); //false
```
2. instanceof operator:
The instanceof operator is used to check the type of an array at run time. It returns true if the type of a variable is an Array other false for other type.
```javascript
const numbers = [1, 2, 3];
const user = { name: "John" };
console.log(numbers instanceof Array); // true
console.log(user instanceof Array); // false
```
3. Checking constructor type:
The constructor property of the variable is used to determine whether the variable Array type or not.
```javascript
const numbers = [1, 2, 3];
const user = { name: "John" };
console.log(numbers.constructor === Array); // true
console.log(user.constructor === Array); // false
```
**[⬆ Back to Top](#table-of-contents)**
439. ### What is pass by value and pass by reference?
Pass-by-value creates a new space in memory and makes a copy of a value. Primitives such as string, number, boolean etc will actually create a new copy. Hence, updating one value doesn't impact the other value. i.e, The values are independent of each other.
```javascript
let a = 5;
let b = a;
b++;
console.log(a, b); //5, 6
```
In the above code snippet, the value of `a` is assigned to `b` and the variable `b` has been incremented. Since there is a new space created for variable `b`, any update on this variable doesn't impact the variable `a`.
Pass by reference doesn't create a new space in memory but the new variable adopts a memory address of an initial variable. Non-primitives such as objects, arrays and functions gets the reference of the initiable variable. i.e, updating one value will impact the other variable.
```javascript
let user1 = {
name: "John",
age: 27,
};
let user2 = user1;
user2.age = 30;
console.log(user1.age, user2.age); // 30, 30
```
In the above code snippet, updating the `age` property of one object will impact the other property due to the same reference.
**[⬆ Back to Top](#table-of-contents)**
440. ### What are the differences between primitives and non-primitives?
JavaScript language has both primitives and non-primitives but there are few differences between them as below,
| Primitives | Non-primitives |
| -------------------------- | -------------------- |
| These types are predefined | Created by developer |
| These are immutable | Mutable |
| Compare by value | Compare by reference |
| Stored in Stack | Stored in heap |
| Contain certain value | Can contain NULL too |
**[⬆ Back to Top](#table-of-contents)**
441. ### How do you create your own bind method using either call or apply method?
The custom bind function needs to be created on Function prototype inorder to use it as other builtin functions. This custom function should return a function similar to original bind method and the implementation of inner function needs to use apply method call.
The function which is going to bind using custom `myOwnBind` method act as the attached function(`boundTargetFunction`) and argument as the object for `apply` method call.
```js
Function.prototype.myOwnBind = function (whoIsCallingMe) {
if (typeof this !== "function") {
throw new Error(this + "cannot be bound as it's not callable");
}
const boundTargetFunction = this;
return function () {
boundTargetFunction.apply(whoIsCallingMe, arguments);
};
};
```
**[⬆ Back to Top](#table-of-contents)**
442. ### What are the differences between pure and impure functions?
Some of the major differences between pure and impure function are as below,
| Pure function | Impure function |
| ----------------------------------- | --------------------------------------------------------------------- |
| It has no side effects | It causes side effects |
| It is always return the same result | It returns different result on each call |
| Easy to read and debug | Difficult to read and debug because they are affected by extenal code |
**[⬆ Back to Top](#table-of-contents)**
445. ### What is referential transparency?
An expression in javascript that can be replaced by its value without affecting the behaviour of the program is called referential transparency. Pure functions are referentially transparent.
```javascript
const add = (x, y) => x + y;
const multiplyBy2 = (x) => x * 2;
//Now add (2, 3) can be replaced by 5.
multiplyBy2(add(2, 3));
```
**[⬆ Back to Top](#table-of-contents)**
446. ### What are the possible side-effects in javascript?
A side effect is the modification of the state through the invocation of a function or expression. These side effects make our function impure by default. Below are some side effects which make function impure,
- Making an HTTP request. Asynchronous functions such as fetch and promise are impure.
- DOM manipulations
- Mutating the input data
- Printing to a screen or console: For example, console.log() and alert()
- Fetching the current time
- Math.random() calls: Modifies the internal state of Math object
**[⬆ Back to Top](#table-of-contents)**
447. ### What are compose and pipe functions?
The "compose" and "pipe" are two techniques commonly used in functional programming to simplify complex operations and make code more readable. They are not native to JavaScript and higher-order functions. the `compose()` applies right to left any number of functions to the output of the previous function.
**[⬆ Back to Top](#table-of-contents)**
448. ### What is module pattern?
Module pattern is a designed pattern used to wrap a set of variables and functions together in a single scope returned as an object. JavaScript doesn't have access specifiers similar to other languages(Java, Python, etc) to provide private scope. It uses IIFE (Immediately invoked function expression) to allow for private scopes. i.e., a closure that protect variables and methods.
The module pattern looks like below,
```javascript
(function () {
// Private variables or functions goes here.
return {
// Return public variables or functions here.
};
})();
```
Let's see an example of a module pattern for an employee with private and public access,
```javascript
const createEmployee = (function () {
// Private
const name = "John";
const department = "Sales";
const getEmployeeName = () => name;
const getDepartmentName = () => department;
// Public
return {
name,
department,
getName: () => getEmployeeName(),
getDepartment: () => getDepartmentName(),
};
})();
console.log(createEmployee.name);
console.log(createEmployee.department);
console.log(createEmployee.getName());
console.log(createEmployee.getDepartment());
```
**Note:** It mimic the concepts of classes with private variables and methods.
**[⬆ Back to Top](#table-of-contents)**
449. ### What is Function Composition?
It is an approach where the result of one function is passed on to the next function, which is passed to another until the final function is executed for the final result.
```javascript
//example
const double = (x) => x * 2;
const square = (x) => x * x;
var output1 = double(2);
var output2 = square(output1);
console.log(output2);
var output_final = square(double(2));
console.log(output_final);
```
**[⬆ Back to Top](#table-of-contents)**
450. ### How to use await outside of async function prior to ES2022?
Prior to ES2022, if you attempted to use an await outside of an async function resulted in a SyntaxError.
```javascript
await Promise.resolve(console.log("Hello await")); // SyntaxError: await is only valid in async function
```
But you can fix this issue with an alternative IIFE (Immediately Invoked Function Expression) to get access to the feature.
```javascript
(async function () {
await Promise.resolve(console.log("Hello await")); // Hello await
})();
```
In ES2022, you can write top-level await without writing any hacks.
```javascript
await Promise.resolve(console.log("Hello await")); //Hello await
```
**[⬆ Back to Top](#table-of-contents)**
451. ### What is the purpose of the this keyword in JavaScript?
* The `this` keyword in JavaScript is a special variable that is used within a function to refer to the object on which the function is invoked. The value of this depends on how the function is called. It allows functions to access and interact with the object they are bound to.
* The this keyword in JavaScript is a reference to the object that owns or invokes the current function. Its value is determined by the calling context.
**Example 1: this in a Global Context**
```javascript
console.log(this);
```
* In a global context, this refers to the global object (e.g., window in a browser).
**Example 2: this in a Function**
```javascript
function displayThis() {
console.log(this);
}
displayThis();
```
* In a regular function, this refers to the global object.
**Example 3: this in a Method**
```javascript
const person = {
name: 'John',
greet: function() {
console.log('Hello, ' + this.name);
}
};
person.greet();
```
* In a method, this refers to the object that owns the method (person in the case).
**Example 4: this in an Event Handler**
```javascript
document.getElementById('myButton').addEventListener('click', function() {
console.log(this);
});
```
* In an event handler, this refers to the element that triggered the event (the button in this case).
**[⬆ Back to Top](#table-of-contents)**
452. ### What are the uses of closures?
**[⬆ Back to Top](#table-of-contents)**
### Coding Exercise
#### 1. What is the output of below code
```javascript
var car = new Vehicle("Honda", "white", "2010", "UK");
console.log(car);
function Vehicle(model, color, year, country) {
this.model = model;
this.color = color;
this.year = year;
this.country = country;
}
```
- 1: Undefined
- 2: ReferenceError
- 3: null
- 4: {model: "Honda", color: "white", year: "2010", country: "UK"}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The function declarations are hoisted similar to any variables. So the placement for `Vehicle` function declaration doesn't make any difference.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 2. What is the output of below code
```javascript
function foo() {
let x = (y = 0);
x++;
y++;
return x;
}
console.log(foo(), typeof x, typeof y);
```
- 1: 1, undefined and undefined
- 2: ReferenceError: X is not defined
- 3: 1, undefined and number
- 4: 1, number and number
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Of course the return value of `foo()` is 1 due to the increment operator. But the statement `let x = y = 0` declares a local variable x. Whereas y declared as a global variable accidentally. This statement is equivalent to,
```javascript
let x;
window.y = 0;
x = window.y;
```
Since the block scoped variable x is undefined outside of the function, the type will be undefined too. Whereas the global variable `y` is available outside the function, the value is 0 and type is number.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 3. What is the output of below code
```javascript
function main() {
console.log("A");
setTimeout(function print() {
console.log("B");
}, 0);
console.log("C");
}
main();
```
- 1: A, B and C
- 2: B, A and C
- 3: A and C
- 4: A, C and B
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The statements order is based on the event loop mechanism. The order of statements follows the below order,
1. At first, the main function is pushed to the stack.
2. Then the browser pushes the first statement of the main function( i.e, A's console.log) to the stack, executing and popping out immediately.
3. But `setTimeout` statement moved to Browser API to apply the delay for callback.
4. In the meantime, C's console.log added to stack, executed and popped out.
5. The callback of `setTimeout` moved from Browser API to message queue.
6. The `main` function popped out from stack because there are no statements to execute
7. The callback moved from message queue to the stack since the stack is empty.
8. The console.log for B is added to the stack and display on the console.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 4. What is the output of below equality check
```javascript
console.log(0.1 + 0.2 === 0.3);
```
- 1: false
- 2: true
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
This is due to the float point math problem. Since the floating point numbers are encoded in binary format, the addition operations on them lead to rounding errors. Hence, the comparison of floating points doesn't give expected results.
You can find more details about the explanation here [0.30000000000000004.com/](https://0.30000000000000004.com/)
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 5. What is the output of below code
```javascript
var y = 1;
if (function f() {}) {
y += typeof f;
}
console.log(y);
```
- 1: 1function
- 2: 1object
- 3: ReferenceError
- 4: 1undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The main points in the above code snippets are,
1. You can see function expression instead function declaration inside if statement. So it always returns true.
2. Since it is not declared(or assigned) anywhere, f is undefined and typeof f is undefined too.
In other words, it is same as
```javascript
var y = 1;
if ("foo") {
y += typeof f;
}
console.log(y);
```
**Note:** It returns 1object for MS Edge browser
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 6. What is the output of below code
```javascript
function foo() {
return;
{
message: "Hello World";
}
}
console.log(foo());
```
- 1: Hello World
- 2: Object {message: "Hello World"}
- 3: Undefined
- 4: SyntaxError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
This is a semicolon issue. Normally semicolons are optional in JavaScript. So if there are any statements(in this case, return) missing semicolon, it is automatically inserted immediately. Hence, the function returned as undefined.
Whereas if the opening curly brace is along with the return keyword then the function is going to be returned as expected.
```javascript
function foo() {
return {
message: "Hello World",
};
}
console.log(foo()); // {message: "Hello World"}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 7. What is the output of below code
```javascript
var myChars = ["a", "b", "c", "d"];
delete myChars[0];
console.log(myChars);
console.log(myChars[0]);
console.log(myChars.length);
```
- 1: [empty, 'b', 'c', 'd'], empty, 3
- 2: [null, 'b', 'c', 'd'], empty, 3
- 3: [empty, 'b', 'c', 'd'], undefined, 4
- 4: [null, 'b', 'c', 'd'], undefined, 4
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
The `delete` operator will delete the object property but it will not reindex the array or change its length. So the number or elements or length of the array won't be changed.
If you try to print myChars then you can observe that it doesn't set an undefined value, rather the property is removed from the array. The newer versions of Chrome use `empty` instead of `undefined` to make the difference a bit clearer.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 8. What is the output of below code in latest Chrome
```javascript
var array1 = new Array(3);
console.log(array1);
var array2 = [];
array2[2] = 100;
console.log(array2);
var array3 = [, , ,];
console.log(array3);
```
- 1: [undefined × 3], [undefined × 2, 100], [undefined × 3]
- 2: [empty × 3], [empty × 2, 100], [empty × 3]
- 3: [null × 3], [null × 2, 100], [null × 3]
- 4: [], [100], []
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
The latest chrome versions display `sparse array`(they are filled with holes) using this empty x n notation. Whereas the older versions have undefined x n notation.
**Note:** The latest version of FF displays `n empty slots` notation.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 9. What is the output of below code
```javascript
const obj = {
prop1: function () {
return 0;
},
prop2() {
return 1;
},
["prop" + 3]() {
return 2;
},
};
console.log(obj.prop1());
console.log(obj.prop2());
console.log(obj.prop3());
```
- 1: 0, 1, 2
- 2: 0, { return 1 }, 2
- 3: 0, { return 1 }, { return 2 }
- 4: 0, 1, undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
ES6 provides method definitions and property shorthands for objects. So both prop2 and prop3 are treated as regular function values.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 10. What is the output of below code
```javascript
console.log(1 < 2 < 3);
console.log(3 > 2 > 1);
```
- 1: true, true
- 2: true, false
- 3: SyntaxError, SyntaxError,
- 4: false, false
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
The important point is that if the statement contains the same operators(e.g, < or >) then it can be evaluated from left to right.
The first statement follows the below order,
1. console.log(1 < 2 < 3);
2. console.log(true < 3);
3. console.log(1 < 3); // True converted as `1` during comparison
4. True
Whereas the second statement follows the below order,
1. console.log(3 > 2 > 1);
2. console.log(true > 1);
3. console.log(1 > 1); // False converted as `0` during comparison
4. False
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 11. What is the output of below code in non-strict mode
```javascript
function printNumbers(first, second, first) {
console.log(first, second, first);
}
printNumbers(1, 2, 3);
```
- 1: 1, 2, 3
- 2: 3, 2, 3
- 3: SyntaxError: Duplicate parameter name not allowed in this context
- 4: 1, 2, 1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
In non-strict mode, the regular JavaScript functions allow duplicate named parameters. The above code snippet has duplicate parameters on 1st and 3rd parameters.
The value of the first parameter is mapped to the third argument which is passed to the function. Hence, the 3rd argument overrides the first parameter.
**Note:** In strict mode, duplicate parameters will throw a Syntax Error.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 12. What is the output of below code
```javascript
const printNumbersArrow = (first, second, first) => {
console.log(first, second, first);
};
printNumbersArrow(1, 2, 3);
```
- 1: 1, 2, 3
- 2: 3, 2, 3
- 3: SyntaxError: Duplicate parameter name not allowed in this context
- 4: 1, 2, 1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Unlike regular functions, the arrow functions doesn't not allow duplicate parameters in either strict or non-strict mode. So you can see `SyntaxError` in the console.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 13. What is the output of below code
```javascript
const arrowFunc = () => arguments.length;
console.log(arrowFunc(1, 2, 3));
```
- 1: ReferenceError: arguments is not defined
- 2: 3
- 3: undefined
- 4: null
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Arrow functions do not have an `arguments, super, this, or new.target` bindings. So any reference to `arguments` variable tries to resolve to a binding in a lexically enclosing environment. In this case, the arguments variable is not defined outside of the arrow function. Hence, you will receive a reference error.
Where as the normal function provides the number of arguments passed to the function
```javascript
const func = function () {
return arguments.length;
};
console.log(func(1, 2, 3));
```
But If you still want to use an arrow function then rest operator on arguments provides the expected arguments
```javascript
const arrowFunc = (...args) => args.length;
console.log(arrowFunc(1, 2, 3));
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 14. What is the output of below code
```javascript
console.log(String.prototype.trimLeft.name === "trimLeft");
console.log(String.prototype.trimLeft.name === "trimStart");
```
- 1: True, False
- 2: False, True
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
In order to be consistent with functions like `String.prototype.padStart`, the standard method name for trimming the whitespaces is considered as `trimStart`. Due to web web compatibility reasons, the old method name 'trimLeft' still acts as an alias for 'trimStart'. Hence, the prototype for 'trimLeft' is always 'trimStart'
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 15. What is the output of below code
```javascript
console.log(Math.max());
```
- 1: undefined
- 2: Infinity
- 3: 0
- 4: -Infinity
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
-Infinity is the initial comparant because almost every other value is bigger. So when no arguments are provided, -Infinity is going to be returned.
**Note:** Zero number of arguments is a valid case.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 16. What is the output of below code
```javascript
console.log(10 == [10]);
console.log(10 == [[[[[[[10]]]]]]]);
```
- 1: True, True
- 2: True, False
- 3: False, False
- 4: False, True
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
As per the comparison algorithm in the ECMAScript specification(ECMA-262), the above expression converted into JS as below
```javascript
10 === Number([10].valueOf().toString()); // 10
```
So it doesn't matter about number brackets([]) around the number, it is always converted to a number in the expression.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 17. What is the output of below code
```javascript
console.log(10 + "10");
console.log(10 - "10");
```
- 1: 20, 0
- 2: 1010, 0
- 3: 1010, 10-10
- 4: NaN, NaN
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
The concatenation operator(+) is applicable for both number and string types. So if any operand is string type then both operands concatenated as strings. Whereas subtract(-) operator tries to convert the operands as number type.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 18. What is the output of below code
```javascript
console.log([0] == false);
if ([0]) {
console.log("I'm True");
} else {
console.log("I'm False");
}
```
- 1: True, I'm True
- 2: True, I'm False
- 3: False, I'm True
- 4: False, I'm False
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
In comparison operators, the expression `[0]` converted to Number([0].valueOf().toString()) which is resolved to false. Whereas `[0]` just becomes a truthy value without any conversion because there is no comparison operator.
</p>
</details>
#### 19. What is the output of below code
```javascript
console.log([1, 2] + [3, 4]);
```
- 1: [1,2,3,4]
- 2: [1,2][3,4]
- 3: SyntaxError
- 4: 1,23,4
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The + operator is not meant or defined for arrays. So it converts arrays into strings and concatenates them.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 20. What is the output of below code
```javascript
const numbers = new Set([1, 1, 2, 3, 4]);
console.log(numbers);
const browser = new Set("Firefox");
console.log(browser);
```
- 1: {1, 2, 3, 4}, {"F", "i", "r", "e", "f", "o", "x"}
- 2: {1, 2, 3, 4}, {"F", "i", "r", "e", "o", "x"}
- 3: [1, 2, 3, 4], ["F", "i", "r", "e", "o", "x"]
- 4: {1, 1, 2, 3, 4}, {"F", "i", "r", "e", "f", "o", "x"}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Since `Set` object is a collection of unique values, it won't allow duplicate values in the collection. At the same time, it is case sensitive data structure.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 21. What is the output of below code
```javascript
console.log(NaN === NaN);
```
- 1: True
- 2: False
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
JavaScript follows IEEE 754 spec standards. As per this spec, NaNs are never equal for floating-point numbers.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 22. What is the output of below code
```javascript
let numbers = [1, 2, 3, 4, NaN];
console.log(numbers.indexOf(NaN));
```
- 1: 4
- 2: NaN
- 3: SyntaxError
- 4: -1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The `indexOf` uses strict equality operator(===) internally and `NaN === NaN` evaluates to false. Since indexOf won't be able to find NaN inside an array, it returns -1 always.
But you can use `Array.prototype.findIndex` method to find out the index of NaN in an array or You can use `Array.prototype.includes` to check if NaN is present in an array or not.
```javascript
let numbers = [1, 2, 3, 4, NaN];
console.log(numbers.findIndex(Number.isNaN)); // 4
console.log(numbers.includes(NaN)); // true
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 23. What is the output of below code
```javascript
let [a, ...b,] = [1, 2, 3, 4, 5];
console.log(a, b);
```
- 1: 1, [2, 3, 4, 5]
- 2: 1, {2, 3, 4, 5}
- 3: SyntaxError
- 4: 1, [2, 3, 4]
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
When using rest parameters, trailing commas are not allowed and will throw a SyntaxError.
If you remove the trailing comma then it displays 1st answer
```javascript
let [a, ...b] = [1, 2, 3, 4, 5];
console.log(a, b); // 1, [2, 3, 4, 5]
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 25. What is the output of below code
```javascript
async function func() {
return 10;
}
console.log(func());
```
- 1: Promise {\<fulfilled\>: 10}
- 2: 10
- 3: SyntaxError
- 4: Promise {\<rejected\>: 10}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Async functions always return a promise. But even if the return value of an async function is not explicitly a promise, it will be implicitly wrapped in a promise. The above async function is equivalent to below expression,
```javascript
function func() {
return Promise.resolve(10);
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 26. What is the output of below code
```javascript
async function func() {
await 10;
}
console.log(func());
```
- 1: Promise {\<fulfilled\>: 10}
- 2: 10
- 3: SyntaxError
- 4: Promise {\<resolved\>: undefined}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The await expression returns value 10 with promise resolution and the code after each await expression can be treated as existing in a `.then` callback. In this case, there is no return expression at the end of the function. Hence, the default return value of `undefined` is returned as the resolution of the promise. The above async function is equivalent to below expression,
```javascript
function func() {
return Promise.resolve(10).then(() => undefined);
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 27. What is the output of below code
```javascript
function delay() {
return new Promise(resolve => setTimeout(resolve, 2000));
}
async function delayedLog(item) {
await delay();
console.log(item);
}
async function processArray(array) {
array.forEach(item => {
await delayedLog(item);
})
}
processArray([1, 2, 3, 4]);
```
- 1: SyntaxError
- 2: 1, 2, 3, 4
- 3: 4, 4, 4, 4
- 4: 4, 3, 2, 1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Even though “processArray” is an async function, the anonymous function that we use for `forEach` is synchronous. If you use await inside a synchronous function then it throws a syntax error.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 28. What is the output of below code
```javascript
function delay() {
return new Promise((resolve) => setTimeout(resolve, 2000));
}
async function delayedLog(item) {
await delay();
console.log(item);
}
async function process(array) {
array.forEach(async (item) => {
await delayedLog(item);
});
console.log("Process completed!");
}
process([1, 2, 3, 5]);
```
- 1: 1 2 3 5 and Process completed!
- 2: 5 5 5 5 and Process completed!
- 3: Process completed! and 5 5 5 5
- 4: Process completed! and 1 2 3 5
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The forEach method will not wait until all items are finished but it just runs the tasks and goes next. Hence, the last statement is displayed first followed by a sequence of promise resolutions.
But you control the array sequence using for..of loop,
```javascript
async function processArray(array) {
for (const item of array) {
await delayedLog(item);
}
console.log("Process completed!");
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 29. What is the output of below code
```javascript
var set = new Set();
set.add("+0").add("-0").add(NaN).add(undefined).add(NaN);
console.log(set);
```
- 1: Set(4) {"+0", "-0", NaN, undefined}
- 2: Set(3) {"+0", NaN, undefined}
- 3: Set(5) {"+0", "-0", NaN, undefined, NaN}
- 4: Set(4) {"+0", NaN, undefined, NaN}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Set has few exceptions from equality check,
1. All NaN values are equal
2. Both +0 and -0 considered as different values
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 30. What is the output of below code
```javascript
const sym1 = Symbol("one");
const sym2 = Symbol("one");
const sym3 = Symbol.for("two");
const sym4 = Symbol.for("two");
console.log(sym1 === sym2, sym3 === sym4);
```
- 1: true, true
- 2: true, false
- 3: false, true
- 4: false, false
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Symbol follows below conventions,
1. Every symbol value returned from Symbol() is unique irrespective of the optional string.
2. `Symbol.for()` function creates a symbol in a global symbol registry list. But it doesn't necessarily create a new symbol on every call, it checks first if a symbol with the given key is already present in the registry and returns the symbol if it is found. Otherwise a new symbol created in the registry.
**Note:** The symbol description is just useful for debugging purposes.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 31. What is the output of below code
```javascript
const sym1 = new Symbol("one");
console.log(sym1);
```
- 1: SyntaxError
- 2: one
- 3: Symbol('one')
- 4: Symbol
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
`Symbol` is a just a standard function and not an object constructor(unlike other primitives new Boolean, new String and new Number). So if you try to call it with the new operator will result in a TypeError
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 32. What is the output of below code
```javascript
let myNumber = 100;
let myString = "100";
if (!typeof myNumber === "string") {
console.log("It is not a string!");
} else {
console.log("It is a string!");
}
if (!typeof myString === "number") {
console.log("It is not a number!");
} else {
console.log("It is a number!");
}
```
- 1: SyntaxError
- 2: It is not a string!, It is not a number!
- 3: It is not a string!, It is a number!
- 4: It is a string!, It is a number!
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The return value of `typeof myNumber` or `typeof myString` is always a truthy value (either "number" or "string"). The ! operator operates on either `typeof myNumber` or `typeof myString`, converting them to boolean values. Since the value of both `!typeof myNumber` and `!typeof myString` is false, the if condition fails, and control goes to else block.
To make the ! operator operate on the equality expression, one needs to add parentheses:
```
if (!(typeof myNumber === "string"))
```
Or simply use the inequality operator:
```
if (typeof myNumber !== "string")
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 33. What is the output of below code
```javascript
console.log(
JSON.stringify({ myArray: ["one", undefined, function () {}, Symbol("")] })
);
console.log(
JSON.stringify({ [Symbol.for("one")]: "one" }, [Symbol.for("one")])
);
```
- 1: {"myArray":['one', undefined, {}, Symbol]}, {}
- 2: {"myArray":['one', null,null,null]}, {}
- 3: {"myArray":['one', null,null,null]}, "{ [Symbol.for('one')]: 'one' }, [Symbol.for('one')]"
- 4: {"myArray":['one', undefined, function(){}, Symbol('')]}, {}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
The symbols has below constraints,
1. The undefined, Functions, and Symbols are not valid JSON values. So those values are either omitted (in an object) or changed to null (in an array). Hence, it returns null values for the value array.
2. All Symbol-keyed properties will be completely ignored. Hence it returns an empty object({}).
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 34. What is the output of below code
```javascript
class A {
constructor() {
console.log(new.target.name);
}
}
class B extends A {
constructor() {
super();
}
}
new A();
new B();
```
- 1: A, A
- 2: A, B
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Using constructors, `new.target` refers to the constructor (points to the class definition of class which is initialized) that was directly invoked by new. This also applies to the case if the constructor is in a parent class and was delegated from a child constructor.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 35. What is the output of below code
```javascript
const [x, ...y, z] = [1, 2, 3, 4];
console.log(x, y, z);
```
- 1: 1, [2, 3], 4
- 2: 1, [2, 3, 4], undefined
- 3: 1, [2], 3
- 4: SyntaxError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
It throws a syntax error because the rest element should not have a trailing comma. You should always consider using a rest operator as the last element.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 36. What is the output of below code
```javascript
const { a: x = 10, b: y = 20 } = { a: 30 };
console.log(x);
console.log(y);
```
- 1: 30, 20
- 2: 10, 20
- 3: 10, undefined
- 4: 30, undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
The object property follows below rules,
1. The object properties can be retrieved and assigned to a variable with a different name
2. The property assigned a default value when the retrieved value is `undefined`
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 37. What is the output of below code
```javascript
function area({ length = 10, width = 20 }) {
console.log(length * width);
}
area();
```
- 1: 200
- 2: Error
- 3: undefined
- 4: 0
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
If you leave out the right-hand side assignment for the destructuring object, the function will look for at least one argument to be supplied when invoked. Otherwise you will receive an error `Error: Cannot read property 'length' of undefined` as mentioned above.
You can avoid the error with either of the below changes,
1. **Pass at least an empty object:**
```javascript
function area({ length = 10, width = 20 }) {
console.log(length * width);
}
area({});
```
2. **Assign default empty object:**
```javascript
function area({ length = 10, width = 20 } = {}) {
console.log(length * width);
}
area();
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 38. What is the output of below code
```javascript
const props = [
{ id: 1, name: "John" },
{ id: 2, name: "Jack" },
{ id: 3, name: "Tom" },
];
const [, , { name }] = props;
console.log(name);
```
- 1: Tom
- 2: Error
- 3: undefined
- 4: John
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
It is possible to combine Array and Object destructuring. In this case, the third element in the array props accessed first followed by name property in the object.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 39. What is the output of below code
```javascript
function checkType(num = 1) {
console.log(typeof num);
}
checkType();
checkType(undefined);
checkType("");
checkType(null);
```
- 1: number, undefined, string, object
- 2: undefined, undefined, string, object
- 3: number, number, string, object
- 4: number, number, number, number
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
If the function argument is set implicitly(not passing argument) or explicitly to undefined, the value of the argument is the default parameter. Whereas for other falsy values('' or null), the value of the argument is passed as a parameter.
Hence, the result of function calls categorized as below,
1. The first two function calls logs number type since the type of default value is number
2. The type of '' and null values are string and object type respectively.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 40. What is the output of below code
```javascript
function add(item, items = []) {
items.push(item);
return items;
}
console.log(add("Orange"));
console.log(add("Apple"));
```
- 1: ['Orange'], ['Orange', 'Apple']
- 2: ['Orange'], ['Apple']
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Since the default argument is evaluated at call time, a new object is created each time the function is called. So in this case, the new array is created and an element pushed to the default empty array.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 41. What is the output of below code
```javascript
function greet(greeting, name, message = greeting + " " + name) {
console.log([greeting, name, message]);
}
greet("Hello", "John");
greet("Hello", "John", "Good morning!");
```
- 1: SyntaxError
- 2: ['Hello', 'John', 'Hello John'], ['Hello', 'John', 'Good morning!']
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Since parameters defined earlier are available to later default parameters, this code snippet doesn't throw any error.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 42. What is the output of below code
```javascript
function outer(f = inner()) {
function inner() {
return "Inner";
}
}
outer();
```
- 1: ReferenceError
- 2: Inner
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
The functions and variables declared in the function body cannot be referred from default value parameter initializers. If you still try to access, it throws a run-time ReferenceError(i.e, `inner` is not defined).
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 43. What is the output of below code
```javascript
function myFun(x, y, ...manyMoreArgs) {
console.log(manyMoreArgs);
}
myFun(1, 2, 3, 4, 5);
myFun(1, 2);
```
- 1: [3, 4, 5], undefined
- 2: SyntaxError
- 3: [3, 4, 5], []
- 4: [3, 4, 5], [undefined]
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
The rest parameter is used to hold the remaining parameters of a function and it becomes an empty array if the argument is not provided.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 44. What is the output of below code
```javascript
const obj = { key: "value" };
const array = [...obj];
console.log(array);
```
- 1: ['key', 'value']
- 2: TypeError
- 3: []
- 4: ['key']
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Spread syntax can be applied only to iterable objects. By default, Objects are not iterable, but they become iterable when used in an Array, or with iterating functions such as `map(), reduce(), and assign()`. If you still try to do it, it still throws `TypeError: obj is not iterable`.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 45. What is the output of below code
```javascript
function* myGenFunc() {
yield 1;
yield 2;
yield 3;
}
var myGenObj = new myGenFunc();
console.log(myGenObj.next().value);
```
- 1: 1
- 2: undefined
- 3: SyntaxError
- 4: TypeError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
Generators are not constructible type. But if you still proceed to do, there will be an error saying "TypeError: myGenFunc is not a constructor"
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 46. What is the output of below code
```javascript
function* yieldAndReturn() {
yield 1;
return 2;
yield 3;
}
var myGenObj = yieldAndReturn();
console.log(myGenObj.next());
console.log(myGenObj.next());
console.log(myGenObj.next());
```
- 1: { value: 1, done: false }, { value: 2, done: true }, { value: undefined, done: true }
- 2: { value: 1, done: false }, { value: 2, done: false }, { value: undefined, done: true }
- 3: { value: 1, done: false }, { value: 2, done: true }, { value: 3, done: true }
- 4: { value: 1, done: false }, { value: 2, done: false }, { value: 3, done: true }
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
A return statement in a generator function will make the generator finish. If a value is returned, it will be set as the value property of the object and done property to true. When a generator is finished, subsequent next() calls return an object of this form: `{value: undefined, done: true}`.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 47. What is the output of below code
```javascript
const myGenerator = (function* () {
yield 1;
yield 2;
yield 3;
})();
for (const value of myGenerator) {
console.log(value);
break;
}
for (const value of myGenerator) {
console.log(value);
}
```
- 1: 1,2,3 and 1,2,3
- 2: 1,2,3 and 4,5,6
- 3: 1 and 1
- 4: 1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The generator should not be re-used once the iterator is closed. i.e, Upon exiting a loop(on completion or using break & return), the generator is closed and trying to iterate over it again does not yield any more results. Hence, the second loop doesn't print any value.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 48. What is the output of below code
```javascript
const num = 0o38;
console.log(num);
```
- 1: SyntaxError
- 2: 38
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
If you use an invalid number(outside of 0-7 range) in the octal literal, JavaScript will throw a SyntaxError. In ES5, it treats the octal literal as a decimal number.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 49. What is the output of below code
```javascript
const squareObj = new Square(10);
console.log(squareObj.area);
class Square {
constructor(length) {
this.length = length;
}
get area() {
return this.length * this.length;
}
set area(value) {
this.area = value;
}
}
```
- 1: 100
- 2: ReferenceError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Unlike function declarations, class declarations are not hoisted. i.e, First You need to declare your class and then access it, otherwise it will throw a ReferenceError "Uncaught ReferenceError: Square is not defined".
**Note:** Class expressions also applies to the same hoisting restrictions of class declarations.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 50. What is the output of below code
```javascript
function Person() {}
Person.prototype.walk = function () {
return this;
};
Person.run = function () {
return this;
};
let user = new Person();
let walk = user.walk;
console.log(walk());
let run = Person.run;
console.log(run());
```
- 1: undefined, undefined
- 2: Person, Person
- 3: SyntaxError
- 4: Window, Window
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
When a regular or prototype method is called without a value for **this**, the methods return an initial this value if the value is not undefined. Otherwise global window object will be returned. In our case, the initial `this` value is undefined so both methods return window objects.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 51. What is the output of below code
```javascript
class Vehicle {
constructor(name) {
this.name = name;
}
start() {
console.log(`${this.name} vehicle started`);
}
}
class Car extends Vehicle {
start() {
console.log(`${this.name} car started`);
super.start();
}
}
const car = new Car("BMW");
console.log(car.start());
```
- 1: SyntaxError
- 2: BMW vehicle started, BMW car started
- 3: BMW car started, BMW vehicle started
- 4: BMW car started, BMW car started
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
The super keyword is used to call methods of a superclass. Unlike other languages the super invocation doesn't need to be a first statement. i.e, The statements will be executed in the same order of code.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 52. What is the output of below code
```javascript
const USER = { age: 30 };
USER.age = 25;
console.log(USER.age);
```
- 1: 30
- 2: 25
- 3: Uncaught TypeError
- 4: SyntaxError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Even though we used constant variables, the content of it is an object and the object's contents (e.g properties) can be altered. Hence, the change is going to be valid in this case.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 53. What is the output of below code
```javascript
console.log("🙂" === "🙂");
```
- 1: false
- 2: true
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Emojis are unicodes and the unicode for smile symbol is "U+1F642". The unicode comparision of same emojies is equivalent to string comparison. Hence, the output is always true.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 54. What is the output of below code?
```javascript
console.log(typeof typeof typeof true);
```
- 1: string
- 2: boolean
- 3: NaN
- 4: number
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
The typeof operator on any primitive returns a string value. So even if you apply the chain of typeof operators on the return value, it is always string.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 55. What is the output of below code?
```javascript
let zero = new Number(0);
if (zero) {
console.log("If");
} else {
console.log("Else");
}
```
- 1: If
- 2: Else
- 3: NaN
- 4: SyntaxError
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
1. The type of operator on new Number always returns object. i.e, typeof new Number(0) --> object.
2. Objects are always truthy in if block
Hence the above code block always goes to if section.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 55. What is the output of below code in non strict mode?
```javascript
let msg = "Good morning!!";
msg.name = "John";
console.log(msg.name);
```
- 1: ""
- 2: Error
- 3: John
- 4: Undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
It returns undefined for non-strict mode and returns Error for strict mode. In non-strict mode, the wrapper object is going to be created and get the mentioned property. But the object get disappeared after accessing the property in next line.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 56. What is the output of below code?
```javascript
let count = 10;
(function innerFunc() {
if (count === 10) {
let count = 11;
console.log(count);
}
console.log(count);
})();
```
- 1: 11, 10
- 2: 11, 11
- 3: 10, 11
- 4: 10, 10
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
11 and 10 is logged to the console.
The innerFunc is a closure which captures the count variable from the outerscope. i.e, 10. But the conditional has another local variable `count` which overwrites the ourter `count` variable. So the first console.log displays value 11.
Whereas the second console.log logs 10 by capturing the count variable from outerscope.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 57. What is the output of below code ?
- 1: console.log(true && 'hi');
- 2: console.log(true && 'hi' && 1);
- 3: console.log(true && '' && 0);
<details><summary><b>Answer</b></summary>
- 1: hi
- 2: 1
- 3: ''
Reason : The operator returns the value of the first falsy operand encountered when evaluating from left to right, or the value of the last operand if they are all truthy.
**Note:** Below these values are consider as falsy value
- 1: 0
- 2: ''
- 3: null
- 4: undefined
- 5: NAN
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 58. What is the output of below code ?
```javascript
let arr = [1, 2, 3];
let str = "1,2,3";
console.log(arr == str);
```
- 1: false
- 2: Error
- 3: true
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Arrays have their own implementation of `toString` method that returns a comma-separated list of elements. So the above code snippet returns true. In order to avoid conversion of array type, we should use === for comparison.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 59. What is the output of below code?
```javascript
getMessage();
var getMessage = () => {
console.log("Good morning");
};
```
- 1: Good morning
- 2: getMessage is not a function
- 3: getMessage is not defined
- 4: Undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Hoisting will move variables and functions to be the top of scope. Even though getMessage is an arrow function the above function will considered as a varible due to it's variable declaration or assignment. So the variables will have undefined value in memory phase and throws an error '`getMessage` is not a function' at the code execution phase.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 60. What is the output of below code?
```javascript
let quickPromise = Promise.resolve();
quickPromise.then(() => console.log("promise finished"));
console.log("program finished");
```
- 1: program finished
- 2: Cannot predict the order
- 3: program finished, promise finished
- 4: promise finished, program finished
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Even though a promise is resolved immediately, it won't be executed immediately because its **.then/catch/finally** handlers or callbacks(aka task) are pushed into the queue. Whenever the JavaScript engine becomes free from the current program, it pulls a task from the queue and executes it. This is the reason why last statement is printed first before the log of promise handler.
**Note:** We call the above queue as "MicroTask Queue"
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 61. What is the output of below code?
```javascript
console
.log("First line")
[("a", "b", "c")].forEach((element) => console.log(element));
console.log("Third line");
```
- 1: `First line`, then print `a, b, c` in a new line, and finally print `Third line` as next line
- 2: `First line`, then print `a, b, c` in a first line, and print `Third line` as next line
- 3: Missing semi-colon error
- 4: Cannot read properties of undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
When JavaScript encounters a line break without a semicolon, the JavaScript parser will automatically add a semicolon based on a set of rules called `Automatic Semicolon Insertion` which determines whether line break as end of statement or not to insert semicolon. But it does not assume a semicolon before square brackets [...]. So the first two lines considered as a single statement as below.
```javascript
console
.log("First line")
[("a", "b", "c")].forEach((element) => console.log(element));
```
Hence, there will be **cannot read properties of undefined** error while applying the array square bracket on log function.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 62. Write a function that returns a random HEX color
<details><summary><b>Solution 1 (Iterative generation)</b></summary>
<p>
```javascript
const HEX_ALPHABET = [
"0",
"1",
"2",
"3",
"4",
"5",
"6",
"7",
"8",
"9",
"a",
"b",
"c",
"d",
"e",
"f",
];
const HEX_PREFIX = "#";
const HEX_LENGTH = 6;
function generateRandomHex() {
let randomHex = "";
for (let i = 0; i < HEX_LENGTH; i++) {
const randomIndex = Math.floor(Math.random() * HEX_ALPHABET.length);
randomHex += HEX_ALPHABET[randomIndex];
}
return HEX_PREFIX + randomHex;
}
```
</p>
</details>
<details><summary><b>Solution 2 (One-liner)</b></summary>
<p>
```javascript
const HEX_PREFIX = "#";
const HEX_RADIX = 16;
const HEX_LENGTH = 6;
function generateRandomHex() {
return (
HEX_PREFIX +
Math.floor(Math.random() * 0xffffff)
.toString(HEX_RADIX)
.padStart(HEX_LENGTH, "0")
);
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 63. What is the output of below code?
```javascript
var of = ["of"];
for (var of of of) {
console.log(of);
}
```
- 1: of
- 2: SyntaxError: Unexpected token of
- 3: SyntaxError: Identifier 'of' has already been declared
- 4: ReferenceError: of is not defined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
In JavaScript, `of` is not considered as a reserved keyword. So the variable declaration with `of` is accepted and prints the array value `of` using for..of loop.
But if you use reserved keyword such as `in` then there will be a syntax error saying `SyntaxError: Unexpected token in`,
```javascript
var in = ['in'];
for(var in in in) {
console.log(in[in]);
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 64. What is the output of below code?
```javascript
const numbers = [11, 25, 31, 23, 33, 18, 200];
numbers.sort();
console.log(numbers);
```
- 1: [11, 18, 23, 25, 31, 33, 200]
- 2: [11, 18, 200, 23, 25, 31, 33]
- 3: [11, 25, 31, 23, 33, 18, 200]
- 4: Cannot sort numbers
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
By default, the sort method sorts elements alphabetically. This is because elemented converted to strings and strings compared in UTF-16 code units order. Hence, you will see the above numbers not sorted as expected. In order to sort numerically just supply a comparator function which handles numeric sorts.
```javascript
const numbers = [11, 25, 31, 23, 33, 18, 200];
numbers.sort((a, b) => a - b);
console.log(numbers);
```
**Note:** Sort() method changes the original array.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 65. What is the output order of below code?
```javascript
setTimeout(() => {
console.log("1");
}, 0);
Promise.resolve("hello").then(() => console.log("2"));
console.log("3");
```
- 1: 1, 2, 3
- 2: 1, 3, 2
- 3: 3, 1, 2
- 4: 3, 2, 1
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
When the JavaScript engine parses the above code, the first two statements are asynchronous which will be executed later and third statement is synchronous statement which will be moved to callstack, executed and prints the number 3 in the console. Next, Promise is native in ES6 and it will be moved to Job queue which has high priority than callback queue in the execution order. At last, since setTimeout is part of WebAPI the callback function moved to callback queue and executed. Hence, you will see number 2 printed first followed by 1.
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 66. What is the output of below code?
```javascript
console.log(name);
console.log(message());
var name = "John";
(function message() {
console.log("Hello John: Welcome");
});
```
- 1: John, Hello John: Welcome
- 2: undefined, Hello John, Welcome
- 3: Reference error: name is not defined, Reference error: message is not defined
- 4: undefined, Reference error: message is not defined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
IIFE(Immediately Invoked Function Expression) is just like any other function expression which won't be hoisted. Hence, there will be a reference error for message call.
The behavior would be the same with below function expression of message1,
```javascript
console.log(name);
console.log(message());
var name = 'John';
var message = function () {
console.log('Hello John: Welcome');
});
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 67. What is the output of below code?
```javascript
message();
function message() {
console.log("Hello");
}
function message() {
console.log("Bye");
}
```
- 1: Reference error: message is not defined
- 2: Hello
- 3: Bye
- 4: Compile time error
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
As part of hoisting, initially JavaScript Engine or compiler will store first function in heap memory but later rewrite or replaces with redefined function content.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 68. What is the output of below code?
```javascript
var currentCity = "NewYork";
var changeCurrentCity = function () {
console.log("Current City:", currentCity);
var currentCity = "Singapore";
console.log("Current City:", currentCity);
};
changeCurrentCity();
```
- 1: NewYork, Singapore
- 2: NewYork, NewYork
- 3: undefined, Singapore
- 4: Singapore, Singapore
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
Due to hositing feature, the variables declared with `var` will have `undefined` value in the creation phase so the outer variable `currentCity` will get same `undefined` value. But after few lines of code JavaScript engine found a new function call(`changeCurrentCity()`) to update the current city with `var` re-declaration. Since each function call will create a new execution context, the same variable will have `undefined` value before the declaration and new value(`Singapore`) after the declarion. Hence, the value `undefined` print first followed by new value `Singapore` in the execution phase.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 69. What is the output of below code in an order?
```javascript
function second() {
var message;
console.log(message);
}
function first() {
var message = "first";
second();
console.log(message);
}
var message = "default";
first();
console.log(message);
```
- 1: undefined, first, default
- 2: default, default, default
- 3: first, first, default
- 4: undefined, undefined, undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Each context(global or functional) has it's own variable environment and the callstack of variables in a LIFO order. So you can see the message variable value from second, first functions in an order followed by global context message variable value at the end.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 70. What is the output of below code?
```javascript
var expressionOne = function functionOne() {
console.log("functionOne");
};
functionOne();
```
- 1: functionOne is not defined
- 2: functionOne
- 3: console.log("functionOne")
- 4: undefined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
The function call `functionOne` is not going to be part of scope chain and it has it's own execution context with the enclosed variable environment. i.e, It won't be accessed from global context. Hence, there will be an error while invoking the function as `functionOne is not defined`.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 71. What is the output of below code?
```javascript
const user = {
name: "John",
eat() {
console.log(this);
var eatFruit = function () {
console.log(this);
};
eatFruit();
},
};
user.eat();
```
- 1: {name: "John", eat: f}, {name: "John", eat: f}
- 2: Window {...}, Window {...}
- 3: {name: "John", eat: f}, undefined
- 4: {name: "John", eat: f}, Window {...}
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
`this` keyword is dynamic scoped but not lexically scoped . In other words, it doesn't matter where `this` has been written but how it has been invoked really matter. In the above code snippet, the `user` object invokes `eat` function so `this` keyword refers to `user` object but `eatFruit` has been invoked by `eat` function and `this` will have default `Window` object.
The above pit fall fixed by three ways,
1. In ES6, the arrow function will make `this` keyword as lexically scoped. Since the surrounding object of `this` object is `user` object, the `eatFruit` function will contain `user` object for `this` object.
```javascript
const user = {
name: "John",
eat() {
console.log(this);
var eatFruit = () => {
console.log(this);
};
eatFruit();
},
};
user.eat();
```
The next two solutions have been used before ES6 introduced.
2. It is possible create a reference of `this` into a separate variable and use that new variable inplace of `this` keyword inside `eatFruit` function. This is a common practice in jQuery and AngularJS before ES6 introduced.
```javascript
const user = {
name: "John",
eat() {
console.log(this);
var self = this;
var eatFruit = () => {
console.log(self);
};
eatFruit();
},
};
user.eat();
```
3. The `eatFruit` function can bind explicitly with `this` keyword where it refers `Window` object.
```javascript
const user = {
name: "John",
eat() {
console.log(this);
var eatFruit = function () {
console.log(this);
};
return eatFruit.bind(this);
},
};
user.eat()();
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 72. What is the output of below code?
```javascript
let message = "Hello World!";
message[0] = "J";
console.log(message);
let name = "John";
name = name + " Smith";
console.log(name);
```
- 1: Jello World!, John Smith
- 2: Jello World!, John
- 3: Hello World!, John Smith
- 4: Hello World!, John
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
In JavaScript, primitives are immutable i.e. there is no way to change a primitive value once it gets created. So when you try to update the string's first character, there is no change in the string value and prints the same initial value `Hello World!`. Whereas in the later example, the concatenated value is re-assigned to the same variable which will result into creation of new memory block with the reference pointing to `John Smith` value and the old memory block value(`John`) will be garbage collected.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 73. What is the output of below code?
```javascript
let user1 = {
name: "Jacob",
age: 28,
};
let user2 = {
name: "Jacob",
age: 28,
};
console.log(user1 === user2);
```
- 1: True
- 2: False
- 3: Compile time error
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
In JavaScript, the variables such as objects, arrays and functions comes under pass by reference. When you try to compare two objects with same content, it is going to compare memory address or reference of those variables. These variables always create separate memory blocks hence the comparison is always going to return false value.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 74. What is the output of below code?
```javascript
function greeting() {
setTimeout(function () {
console.log(message);
}, 5000);
const message = "Hello, Good morning";
}
greeting();
```
- 1: Undefined
- 2: Reference error:
- 3: Hello, Good morning
- 4: null
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
The variable `message` is still treated as closure(since it has been used in inner function) eventhough it has been declared after setTimeout function. The function with in setTimeout function will be sent to WebAPI and the variable declaration executed with in 5 seconds with the assigned value. Hence, the text declared for the variable will be displayed.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 75. What is the output of below code?
```javascript
const a = new Number(10);
const b = 10;
console.log(a === b);
```
- 1: False
- 2: True
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 1
Eventhough both variables `a` and `b` refer a number value, the first declaration is based on constructor function and the type of the variable is going to be `object` type. Whereas the second declaration is primitive assignment with a number and the type is `number` type. Hence, the equality operator `===` will output `false` value.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 76. What is the type of below function?
```javascript
function add(a, b) {
console.log("The input arguments are: ", a, b);
return a + b;
}
```
- 1: Pure function
- 2: Impure function
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
Eventhough the above function returns the same result for the same arguments(input) that are passed in the function, the `console.log()` statement causes a function to have side effects because it affects the state of an external code. i.e, the `console` object's state and depends on it to perform the job. Hence, the above function considered as impure function.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 77. What is the output of below code?
```javascript
const promiseOne = new Promise((resolve, reject) => setTimeout(resolve, 4000));
const promiseTwo = new Promise((resolve, reject) => setTimeout(reject, 4000));
Promise.all([promiseOne, promiseTwo]).then((data) => console.log(data));
```
- 1: [{status: "fullfilled", value: undefined}, {status: "rejected", reason: undefined}]
- 2: [{status: "fullfilled", value: undefined}, Uncaught(in promise)]
- 3: Uncaught (in promise)
- 4: [Uncaught(in promise), Uncaught(in promise)]
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
The above promises settled at the same time but one of them resolved and other one rejected. When you use `.all` method on these promises, the result will be short circuted by throwing an error due to rejection in second promise. But If you use `.allSettled` method then result of both the promises will be returned irrespective of resolved or rejected promise status without throwing any error.
```javascript
Promise.allSettled([promiseOne, promiseTwo]).then((data) => console.log(data));
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 78. What is the output of below code?
```javascript
try {
setTimeout(() => {
console.log("try block");
throw new Error(`An exception is thrown`);
}, 1000);
} catch (err) {
console.log("Error: ", err);
}
```
- 1: try block, Error: An exception is thrown
- 2: Error: An exception is thrown
- 3: try block, Uncaught Error: Exception is thrown
- 4: Uncaught Error: Exception is thrown
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 3
If you put `setTimeout` and `setInterval` methods inside the try clause and an exception is thrown, the catch clause will not catch any of them. This is because the try...catch statement works synchronously, and the function in the above code is executed asynchronously after a certain period of time. Hence, you will see runtime exception without catching the error. To resolve this issue, you have to put the try...catch block inside the function as below,
```javascript
setTimeout(() => {
try {
console.log("try block");
throw new Error(`An exception is thrown`);
} catch (err) {
console.log("Error: ", err);
}
}, 1000);
```
You can use `.catch()` function in promises to avoid these issues with asynchronous code.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 79. What is the output of below code?
```javascript
let a = 10;
if (true) {
let a = 20;
console.log(a, "inside");
}
console.log(a, "outside");
```
- 1: 20, "inside" and 20, "outside"
- 2: 20, "inside" and 10, "outside"
- 3: 10, "inside" and 10, "outside"
- 4: 10, "inside" and 20, "outside"
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 2
The variable "a" declared inside "if" has block scope and does not affect the value of the outer "a" variable.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 80. What is the output of below code?
```javascript
let arr = [1, 2, 3, 4, 5, -6, 7];
arr.length = 0;
console.log(arr);
```
- 1: 0
- 2: Undefined
- 3: null
- 4: [ ]
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The length of the array 'arr' has been set to 0, so the array becomes empty.
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
#### 81. How do you verify two strings are anagrams?
An anagram is a word or phrase formed by rearranging all the letters of a different word or phrase exactly once. For example, the anagrams of "eat" word are "tea" and "ate".
You can split each word into characters, followed by sort action and later join them back. After that you can compare those two words to verify whether those two words are anagrams or not.
```javascript
function verifyAnagrams(word1, word2) {
return word1.split("").sort().join("") === word2.split("").sort().join("")
}
console.log(verifyAnagrams("eat", "ate"));
```
**[⬆ Back to Top](#table-of-contents)**
#### 82. What is the output of below code?
```javascript
printHello();
printMessage();
function printHello() {
console.log('Hello')
function printMessage() {
console.log("Good day")
}
}
```
- 1: Hello, Good day
- 2: Reference Error: printHello is not defined, Reference Error: printMessage is not defined
- 3: Reference Error: printHello is not defined, Good day
- 4: Hello, Reference Error: printMessage is not defined
<details><summary><b>Answer</b></summary>
<p>
##### Answer: 4
The function `printHello` is hoisted to the top of the global scope and prints "Hello" to the console. Even `printMessage` function is hoisted, but it is lifted to the local scope(in "printHello") it was declared in. That is the reason you will endup with reference error for second function call.
But if the second function is invoked in the first function itself, there won't be any reference error.
```javascript
printHello();
function printHello() {
printMessage();
console.log('Hello')
function printMessage() {
console.log("Good day")
}
}
```
</p>
</details>
---
**[⬆ Back to Top](#table-of-contents)**
## Disclaimer
The questions provided in this repository are the summary of frequently asked questions across numerous companies. We cannot guarantee that these questions will actually be asked during your interview process, nor should you focus on memorizing all of them. The primary purpose is for you to get a sense of what some companies might ask — do not get discouraged if you don't know the answer to all of them — that is ok!
Good luck with your interview 😊
---
| List of 1000 JavaScript Interview Questions | angular,interview,interview-practice,interview-preparation,interview-questions,javascript,javascript-applications,react,vuejs | 2024-03-29T05:04:39Z | 2024-03-29T05:04:16Z | null | 1 | 0 | 1 | 0 | 0 | 8 | null | null | JavaScript |
micz/ThunderAI | main | #  ThunderAI
ThunderAI is a Thunderbird Addon that uses the capabilities of ChatGPT to enhance email management.
It enables users to analyze, write, correct, and optimize their emails, facilitating more effective and professional communication.
ThunderAI is a tool for anyone looking to improve their email quality, both in content and grammar, making the writing process quicker and more intuitive.
There is no need for an API key and is possibile to use this extension even with a free account!
Starting from version 1.1.0, you can also define your own **custom prompts**! Find out how [here](https://micz.it/thunderdbird-addon-thunderai/custom-prompts/)!
<br>
## Translations
Do you want to help translating this addon?
[Find out how!](https://micz.it/thunderdbird-addon-thunderai/translate/)
<br>
## Changelog
ThunderAI's changes are logged [here](CHANGELOG.md).
<br>
<br>Thanks to:
<ul><li><a href="https://github.com/KudoAI/chatgpt.js">chatgpt.js</a> for providing methods to interact with the ChatGTP frontend.</li>
<li><a href="https://github.com/ali-raheem/Aify">Aify</a> for inspiration and certains methods to process the text from ChatGPT.</li>
</ul>
<i>The specific references are described in the corresponding source files.</i>
| ThunderAI is a Thunderbird Addon that uses the capabilities of ChatGPT to enhance email management. | chatgpt,thunderbird,thunderbird-addon,javascript,thunderbird-extension | 2024-03-30T09:44:56Z | 2024-05-22T19:39:25Z | 2024-05-22T19:19:42Z | 1 | 6 | 238 | 11 | 1 | 8 | null | GPL-3.0 | JavaScript |
Daniel-16/recipe-sharing | main | null | This project is a recipe sharing app built using Next.js, Node.js, Express, and MongoDB. Its main purpose is to provide users with a platform to share their recipes and receive votes for their creations. | express,javascript,jsonwebtoken,mongodb,mongoose,nextjs,nodejs,react,typescript | 2024-04-05T19:59:07Z | 2024-05-23T11:34:27Z | null | 1 | 47 | 99 | 0 | 2 | 8 | null | null | TypeScript |
celelab/hackjs | main | <div align="center"><a name="readme-top"></a>
<img src="./public/favicon.svg" width="72" height="72" />
# HackJS
HackJS is a free programming challenge platform that is inspired by AdventJS. <br />
It presents a space story full of new JavaScript programming challenges. <br />
[Report Bug](https://github.com/celelab/hackjs/issues) · [Request Feature](https://github.com/celelab/hackjs/issues)
</div>
> \[!IMPORTANT]
>
> **Star Us**, You will receive all release notifications from GitHub without any delay \~ ⭐️
## ⌨️ Local Development
You can use GitHub Codespaces for online development:
[](https://codespaces.new/celelab/hackjs)
Or clone it for local development:
```sh
git clone https://github.com/celelab/hackjs.git
cd hackjs
pnpm install
pnpm dev
```
<div align="right">
[🔼 Back to top](#readme-top)
</div>
## 🤝 Contributing
> \[!NOTE]
>
> For now we are NOT open to code contributions so as not to break the Dev Hackathon regulations, other types of contributions are welcome, such as reporting errors, suggesting new functions
>
<div align="right">
[🔼 Back to top](#readme-top)
</div>
---
Copyright © 2024 [César Leañez](https://github.com/celelab).
<br />
This project is [Apache License 2.0](./LICENSE) licensed.
| Mejorar tus habilidades de programación en JavaScript a través de una variedad de ejercicios prácticos y desafiantes. Desarrollo para la Hackatón del Dev | challenges,hackathon,hackathon-project,javascript,programming,programming-challenges,react,2024,hackjs,astro | 2024-03-24T23:41:51Z | 2024-04-25T07:17:16Z | null | 1 | 0 | 27 | 0 | 1 | 7 | null | NOASSERTION | Astro |
minsion/front-end-interview | main | ## 前端55道常见面试题
### 1、什么是 MVVM、mvc 模型？
MVC: MVC 即 model-view-controller（模型-视图-控制器)是项目的一种分层架构思想，它把复杂的业务逻辑， 抽离为职能单一的小模块，每个模块看似相互独立，其实又各自有相互依赖关系。它的好处是： 保证了模块的智能单一性，方便程序的开发、维护、耦合度低。
mvvm: MVVM：MVVM 即 Model-View-ViewModel，(模型-视图-控制器)它是一种双向数据绑定的模式， 用 viewModel 来建立起 model 数据层和 view 视图层的连接，数据改变会影响视图，视图改变会影响数据
### 2、vue 双向数据绑定的原理？
vue.js 是采用数据劫持结合发布者-订阅者模式的方式，通过Object.defineProperty()来劫持各个属性的setter，getter，在数据变动时发布消息给订阅者，触发相应的监听回调。 具体步骤： 第一步： 需要 observe 的数据对象进行递归遍历，包括子属性对象的属性，都加上 setter 和getter 这样的话，给这个对象的某个值赋值，就会触发 setter，那么就能监听到了数据变化
第二步： compile 解析模板指令，将模板中的变量替换成数据，然后初始化渲染页面视图，并将每个指令对应的节点绑定更新函数，添加监听数据的订阅者，一旦数据有变动，收到通知，更新视图
第三步： Watcher 订阅者是 Observer 和 Compile 之间通信的桥梁，主要做的事情是: 1、在自身实例化时往属性订阅器(dep)里面添加自己 2、自身必须有一个 update() 方法 3、待属性变动 dep.notice() 通知时，能调用自身的 update() 方法，并触发 Compile 中绑定的回调，则功成身退。
第四步：MVVM 作为数据绑定的入口，整合 Observer、Compile 和 Watcher 三者，通过 Observer 来监听自己的 model 数据变化， 通过 Compile 来解析编译模板指令，最终利用 Watcher 搭起 Observer 和 Compile 之间的通信桥梁，达到数据变化 -> 视图更新； 视图交互变化(input) -> 数据 model 变更的双向绑定效果。
### 3、vue 的生命周期有哪些？
vue 实例从创建到销毁的过程就是生命周期。 也就是从开始创建、初始化数据、编译模板、挂在 dom -> 渲染、更新 -> 渲染、准备销毁、销毁等一系列过程 vue 的声明周期常见的主要分为4 大阶段 8 大钩子函数 另外三个生命周期函数不常用 keep-alive 主要用于保留组件状态或避免重新渲染。 activated只有在 keep-alive 组件激活时调用。 deactivated只有在 keep-alive 组件停用时调用。 errorCapured 当捕获一个来自子孙组件的错误时被调用。此钩子会收到三个参数：错误对象、发生错 误的组件实例以及一个包含错误来源信息的字符串。此钩子可以返回 false 以阻止该错误继续向上传 播。
一、创建前 / 后 在beforeCreate生命周期函数执行的时候，data 和 method 还没有初始化 在created 生命周期函数执行的时候， data 和 method 已经初始化完成
二、渲染前/后 在beforeMount 生命周期函数执行的时候，已经编译好了模版字符串、但还没有真正渲染到页面中去 在mounted 生命周期函数执行的时候，已经渲染完，可以看到页面
三、数据更新前/后 在beforeUpdate生命周期函数执行的时候，已经可以拿到最新的数据，但还没渲染到视图中去。 在updated生命周期函数执行的时候，已经把更新后的数据渲染到视图中去了。
四、销毁前/后 在beforeDestroy 生命周期函数执行的时候，实例进入准备销毁的阶段、此时 data 、methods 、指令 等还是可用状态 在destroyed生命周期函数执行的时候，实例已经完成销毁、此时 data 、methods 、指令等都不可用
### 4、v-if 和 v-show 有什么区别？
v-if 是“真正”的条件渲染，因为它会确保在切换过程中条件块内的事件监听器和子组件适当地被销毁和重建， 操作的实际上是 dom 元素的创建或销毁。
v-show 就简单得多——不管初始条件是什么，元素总是会被渲染，并且只是简单地基于 CSS 进行切换， 它操作的是display:none/block属性。
一般来说， v-if 有更高的切换开销，而 v-show 有更高的初始渲染开销。因此，如果需要非常频繁地切换，则使用 v-show 较好； 如果在运行时条件很少改变，则使用 v-if 较好。
### 5、async await 是什么？它有哪些作用？
async await 是es7里面的新语法、它的作用就是 async 用于申明一个 function 是异步的，而 await 用 于等待一个异步方法执行完成。它可以很好的替代promise 中的 then
async 函数返回一个 Promise 对象，可以使用 then 方法添加回调函数。当函数执行的时候，一旦遇 到 await 就会先返回， 等到异步操作完成，再接着执行函数体内后面的语句。
### 6、常用的数组方法有哪些？
concat() 方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。
find() 方法返回数组中满足提供的测试函数的第一个元素的值。否则返回 undefined 。
findIndex() 方法返回数组中满足提供的测试函数的第一个元素的索引。否则返回-1。
includes() 方法用来判断一个数组是否包含一个指定的值，根据情况，如果包含则返回 true， 否则返回 false。
indexOf() 方法返回在数组中可以找到一个给定元素的第一个索引，如果不存在，则返回-1。 （通常用它判断数组中有没有这个元素）
join() 方法将一个数组（或一个类数组对象）的所有元素连接成一个字符串并返回这个字符串。 如果数组只有一个项目，那么将返回该项目而不使用分隔符。
pop() 方法从数组中删除最后一个元素，并返回该元素的值。此方法更改数组的长度。
push() 方法将一个或多个元素添加到数组的末尾，并返回该数组的新长度。
shift() 方法从数组中删除第一个元素，并返回该元素的值。此方法更改数组的长度。
unshift() 方法将一个或多个元素添加到数组的开头，并返回该数组的新长度(该方法修改原有数组)。
splice() 方法通过删除或替换现有元素或者原地添加新的元素来修改数组,并以数组形式返回被修改的内 容。此方法会改变原数组。 由被删除的元素组成的一个数组。如果只删除了一个元素，则返回只包含一个元素的数组。如果没有删 除元素，则返回空数组。
slice() 方法同上，但不会改变原数组
reverse() 方法将数组中元素的位置颠倒，并返回该数组。该方法会改变原数组。
sort() 方法用原地算法对数组的元素进行排序，并返回数组。默认排序顺序是在将元素转换为字 符串，然后比较它们的 UTF-16 代码单元值序列时构建的
### 7、数组有哪几种循环方式？分别有什么作用？
every() 方法测试一个数组内的所有元素是否都能通过某个指定函数的测试。它返回一个布尔 值。
filter() 方法创建一个新数组, 其包含通过所提供函数实现的测试的所有元素。 注意： filter() 不会对空数组进行检测。 注意： filter() 不会改变原始数组。
forEach() 方法对数组的每个元素执行一次提供的函数。
some() 方法测试是否至少有一个元素可以通过被提供的函数方法。该方法返回一个 Boolean 类型 的值。
### 8、常用的字符串方法有哪些？
charAt() 方法从一个字符串中返回指定的字符。
concat() 方法将一个或多个字符串与原字符串连接合并，形成一个新的字符串并返回。
includes() 方法用于判断一个字符串是否包含在另一个字符串中，根据情况返回 true 或 false。
indexOf() 方法返回调用它的 String 对象中第一次出现的指定值的索引，从 fromIndex 处进行搜 索。如果未找到该值，则返回 -1。 match() 方法检索返回一个字符串匹配正则表达式的的结果。
padStart() 方法用另一个字符串填充当前字符串(重复，如果需要的话)，以便产生的字符串达到给定的 长度。填充从当前字符串的开始(左侧)应用的。 (常用于时间补 0)
replace() 方法返回一个由替换值（ replacement ）替换一些或所有匹配的模式（ pattern ）后的新 字符串。模式可以是一个字符串或者一个正则表达式，替换值可以是一个字符串或者一个每次匹配都要 调用的回调函数。 原字符串不会改变。 slice() 方法提取某个字符串的一部分，并返回一个新的字符串，且不会改动原字符串。
split() 方法使用指定的分隔符字符串将一个 String 对象分割成字符串数组，以将字符串分隔为 子字符串，以确定每个拆分的位置。 substr() 方法返回一个字符串中从指定位置开始到指定字符数的字符。 trim() 方法会从一个字符串的两端删除空白字符。在这个上下文中的空白字符是所有的空白字符 (space, tab, no-break space 等) 以及所有行终止符字符（如 LF，CR）。
### 9、什么是原型链？
每一个实例对象上有一个proto 属性，指向的构造函数的原型对象，构造函数的原型 对象也是一个对象， 也有 proto 属性，这样一层一层往上找的过程就形成了原型链。
10、什么是闭包？手写一个闭包函数？ 闭包有哪些优缺点？
闭包（closure）指有权访问另一个函数作用域中变量的函数。简单理解就是 ，一个作用 域可以访问另外一个函数内部的局部变量。
```
function fn() {
var num = 10
function fun() {
console.log(num)
}
return fun
}
var f = fn()
f()
```
作用： 延长变量作用域、在函数的外部可以访问函数内部的局部变量，容易造成内层泄露，因为闭包中 的局部变量永远不会被回收
### 11、常见的继承有哪些？
一、原型链继承
特点： 1、实例可继承的属性有：实例的构造函数的属性，父类构造函数属性，父类原型的属性。（新 实例不会继承父类实例的属性！
缺点： 1、新实例无法向父类构造函数传参。
2、继承单一。
3、所有新实例都会共享父类实例的属性。（原型上的属性是共享的，一个实例修改了原型属 性，另一个实例的原 型属性也会被修改！）
二、借用构造函数继承
重点： 用 .call()和.apply() 将父类构造函数引入子类函数（在子类函数中做了父类函数的自执行（复 制））
特点： 1、只继承了父类构造函数的属性，没有继承父类原型的属性。
2、解决了原型链继承缺点 1、2、3。
3、可以继承多个构造函数属性（call 多个）。
4、在子实例中可向父实例传参。
缺点： 1、只能继承父类构造函数的属性。
2、无法实现构造函数的复用。（每次用每次都要重新调用）
3、每个新实例都有父类构造函数的副本，臃肿。
三、组合继承（组合原型链继承和借用构造函数继承）（常用）
重点： 结合了两种模式的优点，传参和复用
特点： 1、可以继承父类原型上的属性，可以传参，可复用。
2、每个新实例引入的构造函数属性是私有的。
缺点： 调用了两次父类构造函数（耗内存），子类的构造函数会代替原型上的那个父类构造函 数。
四、原型式继承
重点： 用一个函数包装一个对象，然后返回这个函数的调用，这个函数就变成了个可以随意增添属性的 实例或对象。object.create()就是这个原理。
特点： 类似于复制一个对象，用函数来包装。
缺点： 1、所有实例都会继承原型上的属性。 2、无法实现复用。（新实例属性都是后面添加的）
五、class 类实现继承
通过 extends 和 super 实现继承
六、寄生式继承
重点： 就是给原型式继承外面套了个壳子。
优点： 没有创建自定义类型，因为只是套了个壳子返回对象（这个），这个函数顺理成章就成 了创建的新对象。
缺点： 没用到原型，无法复用。
### 12、后台管理系统中的权限管理是怎么实现的？
登录： 当用户填写完账号和密码后向服务端验证是否正确，验证通过之后，服务端会返回一个 token，
拿到 token 之后（我会将这个 token 存贮到 cookie 中，保证刷新页面后能记住用户登录状态），前端会 根据 token 再去拉取一个 user_info 的接口来获取用户的详细信息（如用户权限，用户名等等信息）。
权限验证： 通过 token 获取用户对应的 权限，动态根据用户的 权限算出其对应有权限的路由，通过 router.addRoutes 动态挂载这些路由。
具体思路：
登录成功后，服务端会返回一个 token（该 token 的是一个能唯一标示用户身份的一个 key），之后我 们将 token 存储在本地 cookie 之中，这样下次打开页面或者刷新页面的时候能记住用户的登录状态，不 用再去登录页面重新登录了。
ps:为了保证安全性，我司现在后台所有 token 有效期(Expires/Max-Age)都是 Session，就是当浏览器关 闭了就丢失了。重新打开游览器都需要重新登录验证，后端也会在每周固定一个时间点重新刷新 token，让后台用户全部重新登录一次，确保后台用户不会因为电脑遗失或者其它原因被人随意使用账 号。
用户登录成功之后，我们会在全局钩子 router.beforeEach 中拦截路由，判断是否已获得 token，在 获得 token 之后我们就要去获取用户的基本信息了 页面会先从 cookie 中查看是否存有 token，没有，就走一遍上一部分的流程重新登录，如果有 token, 就会把这个 token 返给后端去拉取 user_info，保证用户信息是最新的。 当然如果是做了单点登录得功 能的话，用户信息存储在本地也是可以的。当你一台电脑登录时，另一台会被提下线，所以总会重新登 录获取最新的内容。
先说一说我权限控制的主体思路，前端会有一份路由表，它表示了每一个路由可访问的权限。当用户登 录之后，通过 token 获取用户的 role ，动态根据用户的 role 算出其对应有权限的路由，再通过 router.addRoutes 动态挂载路由。但这些控制都只是页面级的，说白了前端再怎么做权限控制都不是 绝对安全的，后端的权限验证是逃不掉的。
我司现在就是前端来控制页面级的权限，不同权限的用户显示不同的侧边栏和限制其所能进入的页面(也 做了少许按钮级别的权限控制)，后端则会验证每一个涉及请求的操作，验证其是否有该操作的权限，每 一个后台的请求不管是 get 还是 post 都会让前端在请求 header 里面携带用户的 token，后端会根据 该 token 来验证用户是否有权限执行该操作。若没有权限则抛出一个对应的状态码，前端检测到该状 态码，做出相对应的操作。 使用 vuex 管理路由表，根据 vuex 中可访问的路由渲染侧边栏组件。
具体实现：
创建 vue 实例的时候将vue-router挂载，但这个时候 vue-router 挂载一些登录或者不用权限的公用的页 面。
当用户登录后，获取用role，将 role 和路由表每个页面的需要的权限作比较，生成最终用户可访问的路 由表。
调用router.addRoutes(store.getters.addRouters)添加用户可访问的路由。
使用vuex管理路由表，根据 vuex 中可访问的路由渲染侧边栏组件。
### 13、es6 有哪些新特性？
ES6 是 2015 年推出的一个新的版本、这个版本相对于 ES5 的语法做了很多的优化、例如：新增了let、 const
let 和 const具有块级作用域，不存在变量提升的问题。新增了箭头函数，简化了定义函数的写法，
同时 可以巧用箭头函数的 this、（注意箭头函数本身没有 this,它的 this 取决于外部的环境），
新增了promise 解决了回调地域的问题，新增了模块化、利用 import 、export 来实现导入、导出。
新增了结构赋值， ES6 允许按照一定模式，从数组和对象中提取值，对变量进行赋值，这被称为解构 （Destructuring）。
新增了class 类的概念，它类似于对象。
### 14、v-for 循环为什么一定要绑定 key ?
页面上的标签都对应具体的虚拟 dom 对象(虚拟 dom 就是 js 对象), 循环中 ,如果没有唯一 key , 页面上删除 一条标签, 由于并不知道删除的是那一条! 所以要把全部虚拟 dom 重新渲染, 如果知道 key 为 x 标签被删除 掉, 只需要把渲染的 dom 为 x 的标签去掉即可!
### 15、组件中的 data 为什么要定义成一个函数而不是一个对象？
每个组件都是 Vue 的实例。组件共享 data 属性，当 data 的值是同一个引用类型的值时，改变其中一 个会影响其他
### 16、常见的盒子垂直居中的方法有哪些请举例 3 种？
```
// 1. 利用子绝父相定位的方式来实现
#container {
width: 500px;
height: 500px;
position: relative;
}
#center {
width: 100px;
hight: 100px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -50px;
margin-left: -50px;
}
// 2. 利用 Css3 的 transform，可以轻松的在未知元素的高宽的情况下实现元素的垂直居中。
#container {
position: relative;
}
#center {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}
// 3. flex
#container {
display: flex;
justify-content: center;
align-items: center;
}
#center {
}
```
### 17、平时都是用什么实现跨域的？
jsonp: 利用 标签没有跨域限制的漏洞，网页可以得到从其他来源动态产生的 JSON 数据。JSONP 请求一 定需要对方的服务器做支持才可以。
JSONP 优点是简单兼容性好，可用于解决主流浏览器的跨域数据访问的问题。缺点是仅支持 get 方法具 有局限性,不安全可能会遭受 XSS 攻击。
声明一个回调函数，其函数名(如 show)当做参数值，要传递给跨域请求数据的服务器，函数形参为要获 取目标数据(服务器返回的 data)。 创建一个 script 标签，把那个跨域的 API 数据接口地址，赋值给 script 的 src,还要在这个地址中向服 务器传递该函数名（可以通过问号传参:?callback=show）。
服务器接收到请求后，需要进行特殊的处理：把传递进来的函数名和它需要给你的数据拼接成一个字符 串,例如：传递进去的函数名是 show，它准备好的数据是 show('我不爱你') 。
最后服务器把准备的数据通过 HTTP 协议返回给客户端，客户端再调用执行之前声明的回调函数 （show），对返回的数据进行操作。
CORS：跨域资源共享（CORS）是一种机制；当一个资源访问到另外一个资源(这个资源放在 不同的域名或者不同的协议或者端口)，资源就会发起一个跨域的 HTTP 请求需要浏览器和服务器同时支持；
1.整个 CORS 通信，都是浏览器自动完成。浏览器发现了 AJAX 请求跨源，就会自动添加一些附加的头 信息，有时还会多出一次附加的请求，但用户不会有感觉；
2.实现 CORS 的关键是服务器，只要服务器实现了 CORS 接口，就可以跨源通信
3.服务器对于不同的请求，处理方式不一样； 有简单请求和非简单请求
### 18、cookie 、localstorage 、 sessionstrorage 之间有什么区别？
与服务器交互：
cookie 是网站为了标示用户身份而储存在用户本地终端上的数据（通常经过加密）
cookie 始终会在同源 http 请求头中携带（即使不需要），在浏览器和服务器间来回传递
sessionStorage 和 localStorage 不会自动把数据发给服务器，仅在本地保存
存储大小：
cookie 数据根据不同浏览器限制，大小一般不能超过 4k
sessionStorage 和 localStorage 虽然也有存储大小的限制，但比 cookie 大得多，可以达到 5M 或更大
有期时间：
ocalStorage 存储持久数据，浏览器关闭后数据不丢失除非主动删除数据
sessionStorage 数据在当前浏览器窗口关闭后自动删除
cookie 设置的 cookie 过期时间之前一直有效，与浏览器是否关闭无关
### 19、this 的指向有哪些？
1、普通函数中的 this 指向 window
2、定时器中的 this 指向 window
3、箭头函数没有 this,它的 this 指向取决于外部环境、
4、事件中的 this 指向事件的调用者 黑马程序员
5、 构造函数中 this 和原型对象中的 this,都是指向构造函数 new 出来实例对象
6、类 class 中的 this 指向由 constructor 构造器 new 出来的实例对象
7、自调用函数中的 this 指向 window
### 20、什么是递归，递归有哪些优点或缺点？
递归： 如果一个函数在内部可以调用其本身，那么这个函数就是递归函数。简单理解:函 数内部自己调用自己, 这个函数就是递归函数
优点： 结构清晰、可读性强
缺点： 效率低、调用栈可能会溢出，其实每一次函数调用会在内存栈中分配空间，而每个进程的栈的容 量是有限的，当调用的层次太多时，就会超出栈的容量，从而导致栈溢出。->性能
### 21、谈谈你平时都用了哪些方法进行性能优化？
减少 http 请求次数、打包压缩上线代码、使用懒加载、使用雪碧图、动态渲染组件、CDN 加载包。
### 22、vue 实例是挂载到那个标签上的？
vue 实例最后会挂载在body 标签里面，所以我们在 vue 中是获取不了 body 标签的，如果要使用 body 标 签的话需要用原生的方式获取
### 23、什么是深拷贝、什么是浅拷贝？
浅拷贝： 创建一个新对象，这个对象有着原始对象属性值的一份精确拷贝。如果属性是基本类型，拷贝 的就是基本类型的值，如果属性是引用类型，拷贝的就是内存地址 ，所以如果其中一个对象改变了这个 地址，就会影响到另一个对象。
深拷贝： 会拷贝所有的属性，并拷贝属性指向的动态分配的内存。当对象和它所引用的对象一起拷贝时即 发生深拷贝。 深拷贝相比于浅拷贝速度较慢并且花销较大。拷贝前后两个对象互不影响。
### 24、js 的执行机制是怎么样的？
js 是一个单线程、异步、非阻塞 I/O 模型、 event loop 事件循环的执行机制
所有任务可以分成两种，一种是同步任务（synchronous），另一种是异步任务（asynchronous）。
同步任务指的是，在主线程上排队执行的任务，只有前一个任务执行完毕，才能执行后一个任务。异步 任务指的是，不进入主线程、而进入"任务队列"（task queue）的任务，只有"任务队列"通知主线程， 某个异步任务可以执行了，该任务才会进入主线程执行。
### 25、请写至少三种数组去重的方法？（原生 js）
```
//利用filter
function unique(arr) {
return arr.filter(function (item, index, arr) {
//当前元素，在原始数组中的第一个索引==当前索引值，否则返回当前元素
return arr.indexOf(item, 0) === index
})
}
var arr = [
1,
1,
'true',
'true',
true,
true,
15,
15,
false,
false,
undefined,
undefined,
null,
null,
NaN,
NaN,
'NaN',
0,
0,
'a',
'a',
{},
{}
]
console.log(unique(arr))
//利用ES6 Set去重（ES6中最常用）
function unique(arr) {
return Array.from(new Set(arr))
}
var arr = [
1,
1,
'true',
'true',
true,
true,
15,
15,
false,
false,
undefined,
undefined,
null,
null,
NaN,
NaN,
'NaN',
0,
0,
'a',
'a',
{},
{}
]
console.log(unique(arr))
//[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {}, {}]
//利用for嵌套for，然后splice去重（ES5中最常用）
function unique(arr) {
for (var i = 0; i < arr.length; i++) {
for (var j = i + 1; j < arr.length; j++) {
if (arr[i] == arr[j]) {
//第一个等同于第二个，splice方法删除第二个
arr.splice(j, 1)
j--
}
}
}
return arr
}
var arr = [
1,
1,
'true',
'true',
true,
true,
15,
15,
false,
false,
undefined,
undefined,
null,
null,
NaN,
NaN,
'NaN',
0,
0,
'a',
'a',
{},
{}
]
console.log(unique(arr))
//[1, "true", 15, false, undefined, NaN, NaN, "NaN", "a", {…}, {…}]
//NaN和{}没有去重，两个null直接消失了
```
### 26、请写出至少两种常见的数组排序的方法（原生 js）
```
//快速排序
function quickSort(elements) {
if (elements.length <= 1) {
return elements
}
var pivotIndex = Math.floor(elements.length / 2)
var pivot = elements.splice(pivotIndex, 1)[0]
var left = []
var right = []
for (var i = 0; i < elements.length; i++) {
if (elements[i] < pivot) {
left.push(elements[i])
} else {
right.push(elements[i])
}
}
return quickSort(left).concat([pivot], quickSort(right))
//concat()方法用于连接两个或者多个数组；该方法不会改变现有的数组，而仅仅会返回被连接数组的一个副本。
}
var elements = [3, 5, 6, 8, 2, 4, 7, 9, 1, 10]
document.write(quickSort(elements))
//插入排序
function sort(elements) {
// 假设第0个元素是一个有序数列，第1个以后的是无序数列，
// 所以从第1个元素开始将无序数列的元素插入到有序数列中去
for (var i = 1; i <= elements.length; i++) {
// 升序
if (elements[i] < elements[i - 1]) {
// 取出无序数列中的第i个作为被插入元素
var guard = elements[i]
//记住有序数列的最后一个位置，并且将有序数列的位置扩大一个
var j = i - 1
elements[i] = elements[j]
// 比大小;找到被插入元素所在位置
while (j >= 0 && guard < elements[j]) {
elements[j + 1] = elements[j]
j--
}
elements[j + 1] = guard //插入
}
}
}
var elements = [3, 5, 6, 8, 2, 4, 7, 9, 1, 10]
document.write('没调用之前：' + elements)
document.write('<br>')
sort(elements)
document.write('被调用之后：' + elements)
//冒泡排序
function sort(elements) {
for (var i = 0; i < elements.length - 1; i++) {
for (var j = 0; j < elements.length - 1 - i; j++) {
if (elements[j] > elements[j + 1]) {
var swap = elements[j]
elements[j] = elements[j + 1]
elements[j + 1] = swap
}
}
}
}
var elements = [3, 5, 6, 8, 2, 4, 7, 9, 1, 10]
console.log('before' + elements)
sort(elements)
console.log('after' + elements)
```
### 27、知道 lodash 吗？它有哪些常见的 API ？
官网
Lodash 是一个一致性、模块化、高性能的 JavaScript 实用工具库。 _.cloneDeep 深度拷贝 _.reject 根据条件去除某个元素。 _.drop(array, [n=1] ) 作用：将 array 中的前 n 个元素去掉，然后返回剩余的部分.
### 28、http 的请求方式有哪些？
get、post、put、delete 等
### 29、平时都是用那些工具进行打包的？babel 是什么？
WebPack 是一个模块打包工具，你可以使用 WebPack 管理你的模块依赖，并编绎输出模块们所需的静 态文件。它能够很好地管理、打包 Web 开发中所用到的 HTML、Javascript、CSS 以及各种静态文件（图 片、字体等），让开发过程更加高效。对于不同类型的资源，webpack 有对应的模块加载器。
webpack 模块打包器会分析模块间的依赖关系，最后 生成了优化且合并后的静态资源 babel可以帮助我们转换一些当前浏览器不支持的语法，它会把这些语法转换为低版本的语法以便浏览 器识别。
### 30、谈谈 set 、 map 是什么？
set 是 es6 提供的一种新的数据结构，它类似于数组，但是成员的值都是唯一的。
map 是 es6 提供的一种新的数据结构,它类似于对象，也是键值对的集合，但是键的范围不仅限于字符 串，各种类型的值都可以当做键。也就是说，Object 结构提供了“字符串—值”的对应，Map 结构提供 了“值—值”的对应，是一种更完善的 Hash 结构实现。如果你需要“键值对”的数据结构，Map 比 Object 更合适。
### 31、清除浮动的方法有哪些？
为什么要清除浮动，因为浮动的盒子脱离标准流，如果父盒子没有设置高度的话，下面的盒子就会撑上 来。
1.额外标签法（在最后一个浮动标签后，新加一个标签，给其设置 clear：both；）（不推荐）
2.父级添加 overflow 属性（父元素添加 overflow:hidden）（不推荐）
3.使用 after 伪元素清除浮动（推荐使用）
```
.clearfix:after{/*伪元素是行内元素 正常浏览器清除浮动方法*/
content: "";
display: block;
height: 0;
clear:both;
visibility: hidden;
}
.clearfix{
*zoom: 1;/*ie6清除浮动的方式 *号只有IE6-IE7执行，其他浏览器不执行*/
｝
```
4.使用 before 和 after 双伪元素清除浮动
```
.clearfix:after,
.clearfix:before {
content: '';
display: table;
}
.clearfix:after {
clear: both;
}
.clearfix {
*zoom: 1;
}
```
### 32、常见的布局方法有哪些？他们的优缺点是什么？
页面布局常用的方法有浮动、定位、flex、grid 网格布局、栅格系统布局
浮动： 优点：兼容性好。 缺点：浮动会脱离标准文档流，因此要清除浮动。我们解决好这个问题即可。
绝对定位 优点：快捷。 缺点：导致子元素也脱离了标准文档流，可实用性差。
flex 布局（CSS3 中出现的） 优点：解决上面两个方法的不足，flex 布局比较完美。移动端基本用 flex 布局。
网格布局（grid） CSS3 中引入的布局，很好用。代码量简化了很多。
利用网格布局实现的一个左右 300px 中间自适应的布局
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Document</title>
<style>
html * {
padding: 0;
margin: 0;
}
/* 重要：设置容器为网格布局，宽度为100% */
.layout.grid .left-center-right {
display: grid;
width: 100%;
grid-template-rows: 100px;
grid-template-columns: 300px auto 300px; /* 重要：设置网格为三列，
并设置每列的宽度。即可。*/
}
.layout.grid .left {
background: red;
}
.layout.grid .center {
background: green;
}
.layout.grid .right {
background: blue;
}
</style>
</head>
<body>
<section class="layout grid">
<article class="left-center-right">
<div class="left">我是 left</div>
<div class="center">
<h1>网格布局解决方案</h1>
我是 center
</div>
<div class="right">我是 right</div>
</article>
</section>
</body>
</html>
```
栅格系统布局 优点：可以适用于多端设备
### 33、图片懒加载是怎么实现的？
就是我们先设置图片的 data-set 属性（当然也可以是其他任意的，只要不会发送 http 请求就行了，作用 就是为了存取值）值为其图片路径，由于不是 src，所以不会发送 http 请求。
然后我们计算出页面 scrollTop 的高度和浏览器的高度之和， 如果图片距离页面顶端的坐标 Y（相对于整个页面，而不是浏览 器窗口）小于前两者之和，就说明图片就要显示出来了（合适的时机，当然也可以是其他情况），
这时 候我们再将 data-set 属性替换为 src 属性即可。
### 34、vue 中 computed 和 watch 的区别是什么？
computed计算属性就是为了简化 template 里面模版字符串的计算复杂度、防止模版太过冗余。
它具有 缓存特性 computed 用来监控自己定义的变量，该变量不在 data 里面声明，直接在 computed 里面定义，然后就 可以在页面上进行双向数据绑定展示出结果或者用作其他处理；
watch主要用于监控 vue 实例的变化，它监控的变量当然必须在 data 里面声明才可以，它可以监控一个 变量，也可以是一个对象，一般用于监控路由、input 输入框的值特殊处理等等，它比较适合的场景是 一个数据影响多个数据，它不具有缓存性
watch：监测的是属性值， 只要属性值发生变化，其都会触发执行回调函数来执行一系列操作。
computed：监测的是依赖值，依赖值不变的情况下其会直接读取缓存进行复用，变化的情况下才 会重新计算。
除此之外，有点很重要的区别是：计算属性不能执行异步任务，计算属性必须同步执行。也就是说计算 属性不能向服务器请求或者执行异步任务。如果遇到异步任务，就交给侦听属性。watch 也可以检测 computed 属性。
### 35、vue 中是怎么实现父向子、子向父、兄弟之间的传值的？
父向子传值主要通过的是 props 属性来传值，props 只读
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>父组件向子组件传值--props</title>
<script src="./js/vue.min.js"></script>
</head>
<body>
<div id="app">
<menu-item title="来自父组件的值"></menu-item>
<!-- 在子组件身上绑定自定义属性来接收父组件data中的数据 -->
<menu-item :tit="title"></menu-item>
</div>
<script>
Vue.component('menu-item', {
props: ['tit'], //props用来接收父组件传过来的值
//在props中使用驼峰形式，模版中要改为使用短横线拼接 props里面的值只读，不能修改
//props是单向数据流
data() {
return {}
},
template: '<div>{{tit}}</div>'
})
var vm = new Vue({
el: '#app',
data: {
title: '我是父组件中的数据'
},
methods: {}
})
</script>
</body>
</html>
```
子向父传值 $emit
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<body>
<div id="app">
<!-- 父组件 -->
<div :style='{fontSize:fontSize+"px"}'>{{pmsg}}</div>
<!-- 子组件 -->
<menu-item :parr="parr" @aas="blune"></menu-item>
</div>
<script type="text/javascript" src="js/vue.js"></script>
<script type="text/javascript">
/*
子组件向父组件传值-基本用法
props传递数据原则：单向数据流
*/
Vue.component('menu-item', {
props: ['parr'],
data() {
return {
msg1: '这是子组件传递过来的值'
}
},
template: `
<div>
<ul>
<li v-for="(item,index) in parr" :key="index">{{item}}</li>
</ul>
<button @click='dd'>扩大父组件中字体大小</button>
</div>
`,
methods: {
dd() {
this.$emit('aas', this.msg1)
}
}
})
//$emit
var vm = new Vue({
el: '#app',
data: {
pmsg: '父组件中内容',
parr: ['apple', 'orange', 'banana'],
fontSize: 10
},
methods: {
blune(message) {
this.fontSize += 5
console.log(message)
}
}
})
</script>
</body>
</html>
```
兄弟组件传值 事件总线
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>Document</title>
<script src="./js/vue.min.js"></script>
</head>
<body>
<div id="app">
<brother></brother>
<sister></sister>
</div>
<script>
var enveBus = new Vue()
Vue.component('brother', {
data() {
return {
kk: ''
}
},
methods: {
dd() {
enveBus.$emit('bTs', '这是哥哥给妹妹的爱')
}
},
template: `
<div>
<button @click='dd'>这是一个哥哥组件---{{kk}}</button>
</div>
`,
mounted() {
enveBus.$on('asd', (result) => {
this.kk = result
})
}
})
Vue.component('sister', {
data() {
return {
sis: ''
}
},
template: `
<div>
<button @click="cc">这是一个妹妹组件---{{sis}}</button>
</div>
`,
mounted() {
enveBus.$on('bTs', (message) => {
this.sis = message
})
},
methods: {
cc() {
enveBus.$emit('asd', '这是妹妹对哥哥的爱')
}
}
})
var vm = new Vue({
el: '#app',
data: {},
methods: {}
})
</script>
</body>
</html>
```
### 36、什么 vuex ,谈谈你对它的理解？
首先 vuex 的出现是为了解决 web 组件化开发的过程中，各组件之间传值的复杂和混乱的问题
将我们在多个组件中需要共享的数据放到 store 中，
要获取或格式化数据需要使用 getters，
改变 store 中的数据，使用 mutation，但是只能包含同步的操作，在具体组件里面调用的方式 this.$store.commit('xxxx')
Action 也是改变 store 中的数据，不过是提交的 mutation，并且可以包含异步操作， 在组件中的调 用方式 this.$store.dispatch('xxx') ； 在 actions 里面使用的 commit('调用 mutation')
### 37、数据类型的判断有哪些方法？他们的优缺点及区别是什么？
然后判断数据类型的方法一般可以通过：typeof、instanceof、constructor、toString四种常用方法
不同类型的优缺点 typeof instanceof constructor Object.prototype.toString.call
优点 使用简单 能检测出引用 类型 基本能检测所有 的类型（除了 null 和 undefined） constructor 易被 修改，也不能跨 iframe
缺点 只能检测 出基本类 型（出 null） 不能检测出基 本类型，且不 能跨 iframe constructor 易被 修改，也不能跨 iframe IE6 下，undefined 和 null 均为 Object
### 38、知道 symbol 吗？
ES6 引入新的原始数据类型 Symbol，表示独一无二的值
### 39、请描述一下 ES6 中的 class 类?
es6 中的 class 可以把它看成是 es5 中构造函数的语法糖，它简化了构造函数的写法， 类的共有属性放到 constructor 里面
通过 class 关键字创建类, 类名我们还是习惯性定义首字母大写
类里面有个 constructor 函数,可以接受传递过来的参数,同时返回实例对象
constructor 函数 只要 new 生成实例时,就会自动调用这个函数, 如果我们不写这个函数,类也会自 动生成这个函数
多个函数方法之间不需要添加逗号分隔
生成实例 new 不能省略
语法规范, 创建类 类名后面不要加小括号,生成实例 类名后面加小括号, 构造函数不需要加 function
继承中,如果实例化子类输出一个方法,先看子类有没有这个方法,如果有就先执行子类的
继承中,如果子类里面没有,就去查找父类有没有这个方法,如果有,就执行父类的这个方法(就近 原则)
如果子类想要继承父类的方法,同时在自己内部扩展自己的方法,利用 super 调用 父类的构造函 数,super 必须在子类 this 之前调用
时刻注意 this 的指向问题,类里面的共有的属性和方法一定要加 this 使用.
constructor 中的 this 指向的是 new 出来的实例对象
自定义的方法,一般也指向的 new 出来的实例对象
绑定事件之后 this 指向的就是触发事件的事件源
在 ES6 中类没有变量提升，所以必须先定义类，才能通过类实例化对象
### 40、谈谈盒子模型？
在标准盒子模型中，width 和 height 指的是内容区域的宽度和高度。
增加内边距、边框和外边距不会 影响内容区域的尺寸，但是会增加元素框的总尺寸。
IE 盒子模型中，width 和 height 指的是内容区域+border+padding的宽度和高度。
### 41、promise 是什么？它有哪些作用？
Promise 是异步编程的一种解决方案.简单说就是一个容器，里面保存着某个未来才会结束的事件 （通常是一个异步操作）的结果。从语法上说，Promise 是一个对象，可以从改对象获取异步操 作的消息。 它可以解决回调地狱的问题，也就是异步深层嵌套问题 .catch() 获取异常信息 .finally() 成功与否都会执行（不是正式标准）
```
/*
1. Promise基本使用
我们使用new来构建一个Promise Promise的构造函数接收一个参数，是函数，并
且传入两个参数： resolve，reject， 分别表示异步操作执行成功后的回调函数
和异步操作执行失败后的回调函数
*/
var p = new Promise(function (resolve, reject) {
//2. 这里用于实现异步任务 setTimeout
setTimeout(function () {
var flag = false
if (flag) {
//3. 正常情况
resolve('hello')
} else {
//4. 异常情况
reject('出错了')
}
}, 100)
})
// 5 Promise实例生成以后，可以用then方法指定resolved状态和reject状态的回调函
数
// 在then方法中，你也可以直接return数据而不是Promise对象，在后面的then中就可以
接收到数据了
p.then(
function (data) {
console.log(data)
},
function (info) {
console.log(info)
}
)
```
### 42、vue-cli 2.0 和 3.0 有什么区别？
3.0 把配置 webpack 的文件隐藏了，如果需要配置它需要创建一个 vue.config.js 文件，3.0 是 2018.10 月 出来的
### 43、箭头函数有哪些特征，请简单描述一下它？
箭头函数没有自己的 this，this 指向定义箭头函数时所处的外部执行环境的 this
即使调用call/apply/bind也无法改变箭头函数的 this 箭头函数本身没有名字 箭头函数不能 new，会报错
箭头函数没有 arguments，在箭头函数内访问这个变量访问的是外部执行环境的 arguments 箭头函数没有 prototype
### 44、移动端有哪些常见的问题，都是怎么解决的？
点击事件 300MS 延迟问题 解决方案：下载 fastclick 的包
H5 页面窗口自动调整到设备宽度，并禁止用户缩放页面
```
<meta name="viewport" content="width=device-width,initial-scale=1.0,minimumscale=1.0,maximum-scale=1.0,user-scalable=no"
```
忽略 Android 平台中对邮箱地址的识别
```
<meta name="format-detection" content="email=no" />
```
当网站添加到主屏幕快速启动方式，可隐藏地址栏，仅针对 ios 的 safari
```
<!-- ios7.0版本以后，safari上已看不到效果 -->
<meta name="apple-mobile-web-app-capable" content="yes" />
```
### 45、post 和 get 请求有哪些区别？
GET：一般用于信息获取，使用 URL 传递参数，对所发送信息的数量也有限制，一般在 2000 个字符
POST：一般用于修改服务器上的资源，对所发送的信息没有限制。
GET 方式需要使用 Request.QueryString 来取得变量的值，而 POST 方式通过 Request.Form 来获取变量 的值，也就是说 Get 是通过地址栏来传值，而 Post 是通过提交表单来传值。
然而，在以下情况中，请使用 POST 请求： 无法使用缓存文件（更新服务器上的文件或数据库） 向服务器发送大量数据（POST 没有数据量限制） 发送包含未知字符的用户输入时，POST 比 GET 更稳定也更可靠
### 46、什么是同源策略？
所谓同源策略是浏览器的一种安全机制，来限制不同源的网站不能通信。同源就是域名、协议、端口一 致。
### 47、http 状态码分别代表什么意思？
1xx 表示 HTTP 请求已经接受，继续处理请求
2xx 表示 HTTP 请求已经处理完成(200)
3xx 表示把请求访 问的 URL 重定向到其他目录(304 资源没有发生变化，会重定向到本地资源)
4xx 表示客户端出现错误 (403 禁止访问、404 资源不存在)
5xx 表示服务端出现错误
### 48、BFC 是什么？
BFC（会计格式化上下文），一个创建了新的 BFC 的盒子是独立布局的，盒子内元素的布局不会影响盒 子外面的元素。在同一个 BFC 中的两个相邻的盒子在垂直方向发生 margin 重叠的问题。
BFC 是值浏览器中创建了一个独立的渲染区域，该区域内所有元素的布局不会影响到区域外元素的布 局，这个渲染区域只对块级元素起作用
### 49、token 是什么？（加密）
1. token 也可以称做令牌，一般由 uid+time+sign(签名)+[固定参数] 组成
uid: 用户唯一身份标识
time: 当前时间的时间戳
sign: 签名, 使用 hash/encrypt 压缩成定长的十六进制字符串，以防止第三方恶意拼接
固定参数(可选): 将一些常用的固定参数加入到 token 中是为了避免重复查库
2. token 在客户端一般存放于 localStorage，cookie，或 sessionStorage 中。在服务器一般存于数据 库中
3. token 的认证流程
用户登录，成功后服务器返回Token给客户端。
客户端收到数据后保存在客户端
客户端再次访问服务器，将token放入headers中 或者每次的请求 参数中
服务器端采用filter过滤器校验。校验成功则返回请求数据，校验失败则返回错误码
4. token 可以抵抗 csrf，cookie+session 不行
5.session 时有状态的，一般存于服务器内存或硬盘中，当服务器采用分布式或集群时，session 就会 面对负载均衡问题。负载均衡多服务器的情况，不好确认当前用户是否登录，因为多服务器不共享 session
客户端登陆传递信息给服务端，服务端收到后把用户信息加密（token）传给客户端，客户端将 token 存放于 localStroage 等容器中。客户端每次访问都传递 token，服务端解密 token，就知道这 个用户是谁了。通过 cpu 加解密，服务端就不需要存储 session 占用存储空间，就很好的解决负载 均衡多服务器的问题了。这个方法叫做 JWT(Json Web Token)
### 50、js 的数据类型有哪些？
js 的数据类型分为基本数据类型（string、number、boolean、null、undefined、symbol）和复杂数据类型
基本数据类型的特点：直接存储在栈中的数据
复杂数据类型的特点：存储的是该对象在栈中引用，真实的数据存放在堆内存里
### 51、一个页面从输入 URL 到页面加载显示完成，这个过程中都发生了什么？
01.浏览器查找域名对应的 IP 地址(DNS 查询：浏览器缓存->系统缓存->路由器缓存->ISP DNS 缓存->根 域名服务器)
02.浏览器向 Web 服务器发送一个 HTTP 请求（TCP 三次握手）
03.服务器 301 重定向（从 example.com 重定向到 www.example.com）
04.浏览器跟踪重定向地址，请求另一个带 www 的网址
05.服务器处理请求（通过路由读取资源）
06.服务器返回一个 HTTP 响应（报头中把 Content-type 设置为 'text/html'）
07.浏览器进 DOM 树构建
08.浏览器发送请求获取嵌在 HTML 中的资源（如图片、音频、视频、CSS、JS 等）
09.浏览器显示完成页面
10.浏览器发送异步请求
### 52、安全问题 ：CSRF 和 XSS 攻击？
CSRF （ Cross-site request forgery ）：跨站请求伪造。
方法一、Token 验证：（用的最多）
服务器发送给客户端一个 token ；
客户端提交的表单中带着这个 token 。
如果这个 token 不合法，那么服务器拒绝这个请求。
方法二：隐藏令牌：
把 token 隐藏在 http 的 head 头中。
方法二和方法一有点像，本质上没有太大区别，只是使用方式上有区别。
方法三、Referer 验证：
Referer 指的是页面请求来源。意思是，只接受本站的请求，服务器才做响应； 如果不是，就拦截 XSS（Cross Site Scripting）：跨域脚本攻击。
1.编码： 对用户输入的数据进行 HTML Entity 编码。 如上图所示，把字符转换成 转义字符。 Encode 的作用是将 $var`等一些字符进行转化，使得浏览器在最终输出结果上是一样的
若不进行任何处理，则浏览器会执行 alert 的 js 操作，实现 XSS 注入。进行编码处理之后，L 在浏览 器中的显示结果就是 <script>alert(1)</script> ，实现了将 `$var 作为纯文本进行输出，且 不引起 J avaScript 的执行。
2.过滤： 移除用户输入的和事件相关的属性。如 onerror 可以自动触发攻击，还有 onclick 等。（总而言是，过滤掉一些不安全的内容） 移除用户输入的 Style 节点、 Script 节点、 Iframe 节点。（尤其是 Script 节点，它可是支持跨域的呀，一定要移除）。 3.校正： 避免直接对 HTML Entity 进行解码。 使用 DOM Parse 转换，校正不配对的 DOM 标签。
备注： 我们应该去了解一下 DOM Parse 这个概念，它的作用是把文本解析成 DOM 结构。 比较常用的做法是，通过第一步的编码转成文本，然后第三步转成 DOM 对象，然后经过第二步的过滤。
### 53、CSRF 和 XSS 的区别
区别一：
CSRF ：需要用户先登录网站 A ，获取 cookie
XSS ：不需要登录。
区别二：（原理的区别）
CSRF ：是利用网站 A 本身的漏洞，去请求网站 A 的 api 。
XSS ：是向网站 A 注入 JS 代码，然后执行 JS 里的代码，篡改网站 A 的内容。
### 54、cookie 和 session 的区别
1、cookie 数据存放在客户的浏览器上，session 数据放在服务器上。
2、cookie 不是很安全，别人可以分析存放在本地的 COOKIE 并进行 COOKIE 欺骗
考虑到安全应当使用 session。
3、session 会在一定时间内保存在服务器上。当访问增多，会比较占用你服务器的性能
考虑到减轻服务器性能方面，应当使用 COOKIE。
4、单个 cookie 保存的数据不能超过 4K，很多浏览器都限制一个站点最多保存 20 个 cookie。
5、所以个人建议：
将登陆信息等重要信息存放为 SESSION ;其他信息如果需要保留，可以放在 COOKIE 中
### 55、call、apply、bind 三者的异同
共同点 : 都可以改变 this 指向;
不同点: call 和 apply 会调用函数, 并且改变函数内部 this 指向. call 和 apply传递的参数不一样,call 传递参数使用逗号隔开,apply 使用数组传递 bind 不会调用函数, 可以改变函 数内部 this 指向. 应用场景
call 经常做继承.
apply 经常跟数组有关系. 比如借助于数学对象实现数组最大值最小值
bind 不调用函数,但是还想改变 this 指向. 比如改变定时器内部的 this 指向
| 前端55道常见面试题 | javascript,angular,css,css3,html,html5,react,vue | 2024-04-04T04:03:53Z | 2024-04-05T06:02:16Z | null | 1 | 0 | 13 | 0 | 0 | 7 | null | null | null |
BrennonMeireles/controle-estoque-react | main | # Gerenciador de Estoque de Produtos
Este é um projeto desenvolvido durante uma sprint no curso de Desenvolvimento de Sistemas do SENAI, em resposta a um pedido do professor. O objetivo era criar um sistema de gerenciamento de estoque de produtos genérico, capaz de abranger diversos tipos de produtos.
## Visão Geral
O projeto consiste em um aplicativo web desenvolvido em React com JavaScript, utilizando Vite como ferramenta de construção. Uma API foi criada do zero e hospedada para fornecer os dados necessários para o funcionamento do sistema.
Inspirado em aplicativos de ponto de venda de lojistas, o sistema permite o cadastro, edição, remoção e visualização dos produtos cadastrados. Além disso, há um recurso de alerta que indica quando o estoque de um produto está baixo, exibindo se está abaixo do necessário, negativo, mediano ou adequado.
O projeto foi prototipado no Figma e todo o front-end foi desenvolvido utilizando React no Vite. Optou-se por uma paleta de cores mais claras para tornar a experiência do usuário mais simples e agradável.
## Funcionalidades Principais
- Cadastro de produtos com descrição, preço de custo, marca, nome e SKU.
- Edição e remoção de produtos.
- Visualização dos produtos cadastrados.
- Alerta de estoque baixo.
## Design no Figma
Para acessar o projeto no Figma e conferir a tipografia e paletas de cores utilizadas, [clique aqui](https://www.figma.com/file/m4d3UCMj9tanzaDx6I9k72/Sistema-de-gerenciamento-de-estoque?type=design&node-id=0%3A1&mode=design&t=Td2BPv7sRs0QDZRp-1).
## Tecnologias Utilizadas
- React
- JavaScript (ES6+)
- Vite
- MongoDB (para hospedagem do banco de dados)
## Capturas de Tela
*Tela de Inicio Home*
*Tela de Visualização do Produto*
*Tela de Cadastro de Produtos*
## Como Contribuir
Se deseja contribuir com este projeto, sinta-se à vontade para abrir uma issue ou enviar um pull request.
## Autor
Este projeto foi desenvolvido por Brennon, Gabriel e Anderson e seus colegas como parte do curso de Desenvolvimento de Sistemas do SENAI.
---
****
| Este é um projeto desenvolvido durante uma sprint no curso de Desenvolvimento de Sistemas do SENAI, em resposta a um pedido do professor. O objetivo era criar um sistema de gerenciamento de estoque de produtos genérico, capaz de abranger diversos tipos de produtos. | api,backend,css,frontend,html,html-css-javascript,html5,javascript,node,nodejs | 2024-04-17T14:50:48Z | 2024-05-09T14:59:50Z | null | 3 | 39 | 123 | 0 | 2 | 7 | null | null | JavaScript |
astroneer-team/astroneer | master | <p align="center">
<a href="https://astroneer.dev/" target="blank">
<img src=".github/astroneer.svg" width="120" alt="Astroneer Logo" />
</a>
</p>
<h2 align="center">
Astroneer.js
</h2>
<p align="center">
<img alt="NPM Version" src="https://img.shields.io/npm/v/%40astroneer%2Fcore?style=for-the-badge&labelColor=000000&color=1269F4">
<img alt="NPM License" src="https://img.shields.io/npm/l/%40astroneer%2Fcore?style=for-the-badge&labelColor=000000&color=1269F4">
<img alt="NPM Downloads" src="https://img.shields.io/npm/dm/%40astroneer%2Fcore?style=for-the-badge&labelColor=000000&color=1269F4">
</p>
## Description
**Astroneer is a framework for building [Node.js] server-side applications**. Its goal is to facilitate the creation of server-side applications by providing a simple and easy-to-understand project structure.
## Features
- **Lightweight**: Astroneer is a lightweight framework, which means it has a small footprint and is easy to install. It is ideal for any project, regardless of its size.
- **Native HTTP server**: Astroneer uses the native HTTP server provided by Node.js. The server bootstrap is defined in the [server.ts] file, allowing you to take full control of the server configuration.
- **File-based routing**: Astroneer uses the file system to define the routes of the application. This makes it easy to create and maintain routes. When a file is added to the **routes** directory it is automatically available as a route.
- **Middleware support**: Astroneer supports middleware functions that can be used to perform tasks before or after the route handler is executed.
## Documentation
Check out the full documentation at [website].
## Contributing
Contributions with Astroneer are welcome and encouraged! To get started, please review our [contribution guidelines](CONTRIBUTING.md) to make sure you have a smooth experience contributing to Astroneer.
## Authors
Astroneer is developed and maintained by [Lucas Larangeira].
[Lucas Larangeira]: https://lucaslarangeira.com
[website]: https://astroneer.dev
[server.ts]: https://github.com/astroneer-team/astroneer-templates/blob/master/default/src/server.ts
[Node.js]: https://nodejs.org/en/
| Next-generation framework for building server-side applications with Node.js & TypeScript 🚀 | astroneer,file-based-routing,framework,javascript,javascript-framework,next-generation,node,nodejs,nodejs-framework,typescript | 2024-05-01T01:36:55Z | 2024-05-16T19:57:36Z | null | 1 | 1 | 100 | 0 | 0 | 7 | null | MIT | TypeScript |
EGAMAGZ/paska-ovo | master | # Paska Ovo
A simple javascript library for adding easter eggs to web pages
[](https://jsr.io/@egamagz/paska-ovo)
## Installation
### For Deno
```bash
deno add @egamagz/paska-ovo
```
### For Node.js
```bash
npx jsr add @egamagz/paska-ovo
```
### For Bun
```bash
bunx jsr add @egamagz/paska-ovo
```
### For other package managers
Check the [JSR page for more details](https://jsr.io/@egamagz/paska-ovo).
## Example
```typescript
import { HistoricalCodes, PaskaOvo } from "@egamagz/paska-ovo";
const paskaOvo = new PaskaOvo()
.addCode({
code: HistoricalCodes.BarrelRoll,
onFound: () => {
//...
},
onFinish() {
// ...
},
duration: 1000,
tag: "Barrel Roll"
})
.addCode({
code: HistoricalCodes.Konami,
onFound: () => {
// ...
},
tag: "Konami"
})
.addCode({
code: ["a", "w", "e", "s", "o", "m", "e"],
onFound: () => {
// ...
},
tag: "Awesome"
})
.addCallback((easterEgg) => {
alert(`You found the easter egg: ${easterEgg.tag}`)
});
// Listen to keyboard events
document.getElementById("add-easter-egg").addEventListener("click", () => {
paskaOvo.listen();
});
// Stop listening to keyboard events
document
.getElementById("remove-easter-egg")
.addEventListener("click", () => {
paskaOvo.stop();
});
```
Alternatively, it's possible to define the easter egg using the constructor:
```typescript
import { HistoricalCodes, PaskaOvo } from "@egamagz/paska-ovo";
const paskaOvo = new PaskaOvo({
code: HistoricalCodes.Konami,
onFound: () => {
alert("Gradius");
},
tag: "konami-code",
}).addCallback((easterEgg) => {
console.log("Actual easter egg:", easterEgg.tag);
console.log("Easter egg's code:", easterEgg.code);
});
paskaOvo.listen();
```
Check the [example](https://egamagz.github.io/paska-ovo/) with [source code](https://github.com/EGAMAGZ/paska-ovo/tree/master/example).
## Credits
Inspired by the project [Egg.js](https://github.com/mikeflynn/egg.js) and [La Velada Web](https://github.com/midudev/la-velada-web-oficial). Created by [EGAMAGZ](https://github.com/EGAMAGZ).
## License
MIT License
| A simple javascript library for adding easter eggs to web pages 🥚 | deno,easter-egg,javascript,nodejs,typescript,bun,jsr | 2024-04-17T03:19:17Z | 2024-05-22T03:38:41Z | 2024-05-22T03:38:41Z | 1 | 8 | 64 | 0 | 0 | 7 | null | MIT | TypeScript |
isharadbharadwaj/tic-tac-toe-html-css-js | main | # Tic Tac Toe
A simple web-based Tic Tac Toe game built using HTML, CSS, and JavaScript.
## Description
This project implements a classic Tic Tac Toe game where two players take turns marking spaces in a 3x3 grid. The game indicates when a player wins, loses, or the game ends in a draw. It's a fun and interactive game suitable for players of all ages.
## Features
- User-friendly interface
- Responsive design for various devices
- Real-time feedback on game status (win, lose, draw)
- Easy-to-understand game mechanics
- Built with modern web technologies (HTML, CSS, JavaScript)
- Open-source project, feel free to contribute!
## Screenshots
## How to Play
1. Open the game in your web browser.
2. Two players take turns clicking on the empty cells to mark their moves.
3. The game will indicate when a player wins, loses, or the game ends in a draw.
4. Click the "Restart" button to play again.
## Installation
There is no installation required to play the game. Simply open the `index.html` file in your web browser to start playing.
## Contributing
Contributions are welcome! Feel free to open issues or submit pull requests to improve the game.
## Author
Sharad Bharadwaj
- LinkedIn: [Sharad Bharadwaj](https://www.linkedin.com/in/sharad-bharadwaj/)
| A classic Tic Tac Toe game built with HTML, CSS, and JavaScript. Enjoy real-time feedback on game status. Open-source and beginner-friendly! | bootstrap,confetti-animation,css,html,javascript,jquery,tic-tac-toe,isharadbharadwaj | 2024-03-22T06:55:37Z | 2024-03-22T07:07:37Z | 2024-03-22T07:07:37Z | 1 | 0 | 4 | 0 | 0 | 7 | null | null | JavaScript |
mudachyo/Hamster-Kombat | main | > [!NOTE]
> Контакты: [Telegram](https://t.me/mudachyo)
>
> 🇪🇳 README in english available [here](README-EN.md)
## Как запустить
- Установить в свой бразуер расширение [Resource Override](https://chromewebstore.google.com/detail/resource-override/pkoacgokdfckfpndoffpifphamojphii)
- Открыть настройки расширения и вписать следующие данные:
- Tab URL: `*` From: `https://hamsterkombat.io/js/telegram-web-app.js` To: `https://ktnff.tech/hamsterkombat/telegram-web-app.js`
- 
- Открыть [Бота](https://web.telegram.org/k/#?tgaddr=tg%3A%2F%2Fresolve%3Fdomain%3Dhamster_kombat_bot%26appname%3Dstart%26startapp%3DkentId2475526) и запустить игру
- 
Пожертвование
---
Мы принимаем следующие криптовалюты:
- **TON**: `UQCGUzPN5GnFqWJiYsFtqqLGO75-cBXlOL8f_qbd7yKY2Tzh`
- **USDT**(TRC20): `TFr8CiAPqEnSyoXHtVefWumodcXgjoB8rS`
- **USDT**(TON): `UQCGUzPN5GnFqWJiYsFtqqLGO75-cBXlOL8f_qbd7yKY2Tzh`
- **NOTCOIN**(TON): `UQCGUzPN5GnFqWJiYsFtqqLGO75-cBXlOL8f_qbd7yKY2Tzh`
- **BTC**: `1Mba8xKKVLdcFJdV7jD8Ba3fFn7DWbp4bt`
Пожертвования будут использованы для поддержания/сохранения проекта. | Running Hamster Kombat in your browser | Запуск Hamster Kombat в браузере | bot,coin,farm,hamster,how-to,javascript,kombat,telegram,web,windows | 2024-04-17T14:51:30Z | 2024-05-23T14:32:54Z | null | 1 | 0 | 10 | 0 | 0 | 7 | null | null | JavaScript |
WebRevo/Journey_to_nowhere | main | # Journey_to_nowhere:
Journey to Nowhere is a mesmerizing project built using Three.js and WebGL. It offers an endless, immersive experience where users can explore an infinite world with seamless movement.
# Features
Infinite World: Traverse an endless virtual environment without encountering boundaries.
Smooth Navigation: Enjoy fluid movement and exploration using intuitive controls.
Realistic Graphics: Experience high-quality 3D graphics rendered with Three.js and WebGL.
Customizable Environment: Easily modify elements of the world to create unique experiences.
Installation
To run the project locally, follow these steps:
Clone the repository:
```bash
git clone https://github.com/WebRevo/Journey_to_nowhere.git
```
Navigate to the project directory:
```bash
cd Journey_to_nowhere
```
Install dependencies:
Ensure you have Node.js installed, then run:
```bash
npm install
```
Start the development server:
```bash
npm run dev
```
For Contact: sarathi2021ai@gmail.com
or
Join our Slack Channel: https://join.slack.com/t/team-revoshared_invitezt-23bhnca2e-VEbQiDF8c~1hUYVjsNa06Q
Enjoy Journey To Nowhere...!
| Immersive world built with Three.js and WebGL, offering seamless, boundless exploration. Experience dynamic landscapes, fluid controls, and realistic 3D graphics in a constantly evolving virtual realm. | 3dgraphics,infiniteworld,javascript,threejs,virtualworld,webgl | 2024-04-14T10:07:39Z | 2024-05-17T10:51:08Z | null | 1 | 0 | 3 | 0 | 1 | 7 | null | null | JavaScript |
Sukhendra523/sukhendra523.github.io | master | # My Portfolio
Welcome to my portfolio! This project showcases my skills, projects, and experiences as a web developer.
### Weblink: [Live Website](https://sukhendra523.github.io/)
## Table of Contents
- [Introduction](#introduction)
- [Features](#features)
- [Technologies Used](#technologies-used)
- [Installation](#installation)
- [Usage](#usage)
- [Contributing](#contributing)
- [License](#license)
## Introduction
My Portfolio is a React.js application that serves as an online portfolio to showcase my work, skills, and achievements. It provides an overview of my background, displays my projects, and offers a way to contact me.
## Features
- About Me: An overview of my background, skills, and experiences.
- Projects: A collection of my notable projects with descriptions, screenshots, and links.
- Skills: A list of my technical skills and proficiencies.
- Resume: A link to download my resume.
- Contact: A form to send me messages or inquiries.
## Technologies Used
- React.js: A JavaScript library for building user interfaces.
- HTML5 & CSS3: Markup and styling languages for building web pages.
- JavaScript: A programming language for adding interactivity to web applications.
- Style-Components: A CSS framework for creating responsive and mobile-first designs.
- Git: A version control system for tracking changes and collaborating on projects.
- GitHub Pages: A platform for hosting and deploying web applications.
## Installation
To run this portfolio locally, follow these steps:
1. Clone the repository: `git clone https://github.com/Sukhendra523/sukhendra523.github.io`
2. Navigate to the project directory: `cd sukhendra523.github.io`
3. Install the dependencies: `npm install`
4. Start the development server: `npm start`
5. Open your browser and visit: `http://localhost:3000`
## Usage
After installing and running the project locally, you can navigate through the different sections of the portfolio using the navigation menu. Explore the About Me section to learn more about my background and skills. Visit the Projects section to see detailed information about my projects, including descriptions and screenshots. Use the Contact section to send me a message or inquiry.
## Contributing
Contributions are welcome! If you'd like to contribute to My Portfolio, please follow these steps:
1. Fork the repository.
2. Create a new branch for your feature or bug fix: `git checkout -b my-feature`
3. Commit your changes: `git commit -m 'Add some feature'`
4. Push to the branch: `git push origin my-feature`
5. Open a pull request.
## License
This project is licensed under the [MIT License](LICENSE).
| This is my portfolio website showcasing my education and experience. | css,html5,javascript,portfolio-website,reactjs,threejs | 2024-04-14T07:28:48Z | 2024-05-17T12:34:46Z | null | 3 | 18 | 22 | 0 | 0 | 7 | null | null | JavaScript |
micahdbak/droppr | main | # droppr
**droppr** is a peer-to-peer file transfer service.
Copyright (C) 2024 droppr. All rights reserved.
---
## Current Implementations
[droppr.ca](https://droppr.ca), [droppr.me](https://droppr.me), and [droppr.net](https://droppr.net) all serve the client (see the client directory for source code).
`sc.droppr.net` serves the signal channel (see the signalchannel directory for source code).
`relay.droppr.net` serves the [eturnal](https://eturnal.net) STUN and TURN server, which is configured using the eturnal.yml configuration file.
All of these domains and subdomains point to a central DigitalOcean droplet that uses `nginx` to route incoming requests to different services.
---
# Mountain Madness 2024
## Prompt: A New Perspective
**A new perspective on file transfer.**
Droppr does something that no other transfer websites do: remove the middle-man during data transfer.
This is a *new perspective* to the conventional "cloud storage" model of file transfer, as droppr transfers files in peer-to-peer fashion, without losing security, and retaining file quality.
With droppr, why use the cloud? 🤔
We hope that by using droppr you'll get a new perspective on file transfer, and rethink the benefits of transfer convention.
## IMPORTANT DISCLAIMER
Droppr is very early in development.
Be careful with using browsers other than Google Chrome or Safari, which have very smart and efficient caching systems, especially with large files (>1GB).
In the case of Firefox, droppr is very memory-intensive, and can crash your tabs.
Err on the side of caution and use Chromium or Google Chrome, please!
And don't run important programs in the background, incase your system lags.
If you wish to use Firefox, please don't transfer files >500mB, to be safe.
It will work, it will just be memory-intensive, and might hog system resources.
## Installation
### YouTube demonstration
There is an installation guide for MacOS machines, split in two parts.
It is split in two because I accidentally set `wsRoot` to an IP address without specifying the port.
Not a big mistake; make sure not to do the same. 😉
[MacOS Installation - Part A - YouTube](https://youtu.be/e8SWK_OIZdE)
[MacOS Installation - Part B - YouTube](https://youtu.be/05bvNlZ5wKY)
### Text Guide
To install and run droppr, there are two important parts:
- React Frontend
- Go 'Signal Channel' (Backend)
The frontend compiles to static files, which must be served.
The signal channel must be run as a program in the background as you interact with the frontend.
For the simplest installation, both the frontend and the signal channel should be run on your local machine.
Then you can access the frontend on your local network, as with the signal channel.
### Private (local) IP Address
To run droppr on your local network for cross-device file transfers on the same network, you need to know your **private IP address** (as opposed to your public IP address).
Your private IP address is an address which computers on the same network as you use to communicate with your device.
On a MacOS machine, you can find your private IP address by holding OPTION and clicking on the internet icon in the top right of your computer.
Your private IP address is the first line under your active network:
Alternatively, for Linux, you can use the command `hostname -I` to list IP addresses for your machine.
Mark this IP address down, as you will need to configure some variables for the frontend so that it knows the IP address of the signal channel.
#### Note
If you don't want to perform transfers on different devices on the same network, disregard this step.
You can simply use 'localhost' as the private IP address in later configuration.
Note that this will only allow you to transfer files from one browser tab to another browser tab, on your device only, which is not as cool as cross-device.
### git clone
Clone this repository somewhere on your machine, accessible by a terminal:
`git clone https://github.com/micahdbak/droppr`
Navigate to it in your terminal.
### React Frontend
#### Configure node and npm
For the React frontend, you should use node version 18.
To install the correct versions of node and npm, you should install nvm; please refer to [this installation guide](https://github.com/nvm-sh/nvm?tab=readme-ov-file#installing-and-updating) on how to install it for any UNIX machine.
Once nvm is installed, you can install the correct versions of node and npm with the following commands:
`nvm install 18`.
Once this is complete, the command `npm` should be available.
Verify this by running `npm -v`.
It should display something along the lines of '10.X.X'.
Once node and npm are properly installed, navigate to this repository in your terminal and `cd` into `client`.
Run `npm ci` to install all dependencies. (This might take a couple minutes.)
#### Configure private IP address
Modify the file `src/interface/helpers.js` relative to the client folder of the cloned repository with your favourite text editor.
The beginning of the file should look like:
```javascript
// interface/
// helpers.js
// constants
const wsRoot = 'wss://sc.droppr.net';
...
```
You need to replace the line:
```javascript
const wsRoot = 'wss://sc.droppr.net';
```
With:
```javascript
const wsRoot = 'ws://(your private IP address):5050';
```
Which should look *something* like:
```javascript
const wsRoot = 'ws://192.168.0.127:5050';
```
Where '192.168.0.127' is replaced with the private IP address of your machine that you found in the first step to installation.
#### Build the frontend
Navigating back to the `client` folder, and after `npm ci` was run, run the command `npm run build` to build the frontend.
Once this is finished, run the command `npm run serve` to serve the frontend onto your local machine.
While `npm run serve` is running, the frontend should be visible in your browser at `http://localhost:3000` or `http://(your private IP address):3000`.
For the latter URL, replace (your private IP address) with the IP address discovered beforehand, like '192.168.0.127', for example.
Note that the droppr frontend will not actually transfer files until the Signal Channel is running on your local machine, which is the next step.
### The Signal Channel
Navigate to the `sc` folder at the root of your cloned repository, using your favourite terminal.
In this folder, you should see `main.go`, `go.mod`, `go.sum`, and some other files.
#### Configure Go
To install and then compile this Go program, you need to install `go` on your machine.
Please use [this installation guide](https://go.dev/doc/install) to install the `go` program.
#### Install dependencies
Once Go is installed, run `go get` from within the `sc` folder.
#### Build the Signal Channel
Once this is finished, run `go build main.go` from within the `sc` folder, to build the signal channel.
There should be an executable called `main` now in the folder.
This executable is the signal channel program, and can be run by running the command `./main` from within the `sc` folder.
### Finish
To use droppr, you should open two terminal windows or panes, once you completed the above steps to install and build both the React frontend and the Go Signal Channel.
In one tereminal window, navigate to the `client` folder of this repository, and run `npm run serve`.
In the other terminal window, navigate to the `sc` folder of this repository, and run `./main`.
Droppr should now be available at `http://localhost:3000` in your browser, or at `http://(your private IP address):3000` on other machines on your local network.
If your private IP address was configured properly, then you should be able to perform transfers in droppr from these addresses.
If transfers are not working properly, restart the steps for finding your private (local) IP address and building of the React frontend.
If all else fails, just use `ws://localhost:5050` as the value of `wsRoot` in the `src/interface/helpers.js` file of the React frontend; though you will only be able to transfer files from one browser tab to another browser tab.
Try using droppr now!
You can drop a file onto the website, after which it should display a recipient link (proper communication with the signal channel, and registering of the drop).
You can copy this link by right-clicking and copying the Link URL---**don't click on it, as you will then become the recipient.**
Open this link in another tab, or on another computer if accessing the private IP address of the hosting device, and a transfer should begin instantly.
Watch the summary of MBs transferred, and once the transfer is complete, you can click the download link on the recipient webpage.
## droppr.ca
We have deployed droppr at [droppr.ca](https://droppr.ca) if your local installation doesn't work properly.
Open the recipient link on another device to drop your file.
Droppr.ca will give you a recipient link that you can share to **any device, on any network** to immediately transfer data.
You can copy this link by right-clicking and copying the Link URL---**don't click on it, as you will then become the recipient.**
### Yippee!!
🥳
## Description (Really a Rant)
### Part A
For too long have we transferred files over Google Drive, iCloud, Discord, and dealt with loss of image quality, latency, slow download speeds, and limited storage options.
Not to mention that you must pay for extra access to these services.
We live in an age of the modern internet with high bandwidth and so much address space.
So why are we so dependant on these cloud services?
Why must we forfeit our data to the hands of corporate conglomerations and pesky government bodies!
Bring your data home!!!
Simply transfer!!!
Use Droppr!!!
### Part B
Droppr is built by leveraging WebRTC to facilitate peer-to-peer (p2p) file transfer.
This is fundamentally different to the file transfer methods commonly in use today, where a server stores a file intermittently until it is downloaded by the recipient.
One outlier is AirDrop, however, AirDrop operates solely on Bluetooth.
Thus, AirDrop is limited to the physical space surrounding the device, not to mention the ecosystem it is locked into, namely, Apple's.
This hinders the true potential of device-to-device file transfer.
We have an internet, why don't we use it?
## WebRTC
WebRTC (Web Real Time Communication) is a JavaScript API designed to facilitate the real-time and peer-to-peer connectivity between two browsers, leveraging a server as a middleman to connect these peers, after which, pure peer-to-peer communication is engaged.
WebRTC is typically used for video and audio conferencing, ranging from applications such as Zoom to Discord, however, few seem to take advantage of the Data Channels that WebRTC's spec provides.
This is what Droppr takes advantage of, where no one else does.
## Signal Channel
WebRTC requires that a signal channel server is created to connect the two peers and pass identifying information between the two.
We created a signal channel using Go, that connects with two interested peers over WebSockets.
The server provides a 'drop identifier' that the peers share in common, and that is considered their session.
WebSockets are used to pass credentials for WebRTC back and forth between the peers, until they understand enough about their internet topology such that they can begin communicating in a purely peer-to-peer fashion.
## Data Channels
Once the peer-to-peer connection is established, a data channel is opened where one peer (the dropper) can stream arbitrary data to the other peer (the recipient).
This data channel is completely separate to files, so that must be handled separately.
## Blobs
JavaScript provides the Blob framework for chunking a File into consumable binary parts.
Droppr uses Blobs to convert an input file into chunks, namely, 256 kB chunks, that are then passed through the data channel to be received by the recipient.
The recipient, as they receive these chunks, reconstructs the file by collecting these blobs in sequential order.
Once the transfer is complete, the recipient fully assembles the File, and initiates a download.
At this point, the drop is finished.
| droppr is a peer-to-peer file transfer service built with WebRTC. | golang,javascript,webrtc,websocket,indexeddb,p2p | 2024-03-23T23:29:39Z | 2024-05-04T19:06:25Z | null | 5 | 14 | 76 | 23 | 3 | 7 | null | NOASSERTION | JavaScript |
danieleverest/interview-questions-angular | main | # Angular Interview Questions & Answers
> Click :star:if you like the project and follow [@danieleverest](https://www.facebook.com/profile.php?id=61556352754672) for technical updates.
---
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<a href=https://zerotomastery.io/?utm_source=github&utm_medium=sponsor&utm_campaign=angular-interview-questions>
<img src=https://process.fs.teachablecdn.com/ADNupMnWyR7kCWRvm76Laz/resize=height:70/https://www.filepicker.io/api/file/AKYtjj5SSGyJuyZrkAB2 alt="ZTM Logo" width="100" height="50">
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<p align="center">
<ol>
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---
### Table of Contents
| No. | Questions |
|---- | ---------
|1 | [What is Angular Framework?](#what-is-angular-framework)|
|2 | [What is the difference between AngularJS and Angular?](#what-is-the-difference-between-angularjs-and-angular)|
|3 | [What is TypeScript?](#what-is-typescript)|
|4 | [Write a pictorial diagram of Angular architecture?](#write-a-pictorial-diagram-of-angular-architecture)|
|5 | [What are the key components of Angular?](#what-are-the-key-components-of-angular)|
|6 | [What are directives?](#what-are-directives)|
|7 | [What are components?](#what-are-components)|
|8 | [What are the differences between Component and Directive?](#what-are-the-differences-between-component-and-directive)|
|9 | [What is a template?](#what-is-a-template)|
|10| [What is a module?](#what-is-a-module)|
|11| [What are lifecycle hooks available?](#what-are-lifecycle-hooks-available)|
|12| [What is a data binding?](#what-is-a-data-binding)|
|13| [What is metadata?](#what-is-metadata)|
|14| [What is Angular CLI?](#what-is-angular-cli)|
|15| [What is the difference between constructor and ngOnInit?](#what-is-the-difference-between-constructor-and-ngoninit)|
|16| [What is a service](#what-is-a-service)|
|17| [What is dependency injection in Angular?](#what-is-dependency-injection-in-angular)|
|18| [How is Dependency Hierarchy formed?](#how-is-dependency-hierarchy-formed)|
|19| [What is the purpose of async pipe?](#what-is-the-purpose-of-async-pipe)|
|20| [What is the option to choose between inline and external template file?](#what-is-the-option-to-choose-between-inline-and-external-template-file)|
|21| [What is the purpose of *ngFor directive?](#what-is-the-purpose-of-ngfor-directive)|
|22| [What is the purpose of ngIf directive?](#what-is-the-purpose-of-ngif-directive)|
|23| [What happens if you use script tag inside template?](#what-happens-if-you-use-script-tag-inside-template)|
|24| [What is interpolation?](#what-is-interpolation)|
|25| [What are template expressions?](#what-are-template-expressions)|
|26| [What are template statements?](#what-are-template-statements)|
|27| [How do you categorize data binding types?](#how-do-you-categorize-data-binding-types)|
|28| [What are pipes?](#what-are-pipes)|
|29| [What is a parameterized pipe?](#what-is-a-parameterized-pipe)|
|30| [How do you chain pipes?](#how-do-you-chain-pipes)|
|31| [What is a custom pipe?](#what-is-a-custom-pipe)|
|32| [Give an example of custom pipe?](#give-an-example-of-custom-pipe)|
|33| [What is the difference between pure and impure pipe?](#what-is-the-difference-between-pure-and-impure-pipe)|
|34| [What is a bootstrapping module?](#what-is-a-bootstrapping-module)|
|35| [What are observables?](#what-are-observables)|
|36| [What is HttpClient and its benefits?](#what-is-httpclient-and-its-benefits)|
|37| [Explain on how to use HttpClient with an example?](#explain-on-how-to-use-httpclient-with-an-example)|
|38| [How can you read full response?](#how-can-you-read-full-response)|
|39| [How do you perform Error handling?](#how-do-you-perform-error-handling)|
|40| [What is RxJS?](#what-is-rxjs)|
|41| [What is subscribing?](#what-is-subscribing)|
|42| [What is an observable?](#what-is-an-observable)|
|43| [What is an observer?](#what-is-an-observer)|
|44| [What is the difference between promise and observable?](#what-is-the-difference-between-promise-and-observable)|
|45| [What is multicasting?](#what-is-multicasting)|
|46| [How do you perform error handling in observables?](#how-do-you-perform-error-handling-in-observables)|
|47| [What is the shorthand notation for subscribe method?](#what-is-the-shorthand-notation-for-subscribe-method)|
|48| [What are the utility functions provided by RxJS?](#what-are-the-utility-functions-provided-by-rxjs)|
|49| [What are observable creation functions?](#what-are-observable-creation-functions)|
|50| [What will happen if you do not supply handler for the observer?](#what-will-happen-if-you-do-not-supply-handler-for-the-observer)|
|51| [What are Angular elements?](#what-are-angular-elements)|
|52| [What is the browser support of Angular Elements?](#what-is-the-browser-support-of-angular-elements)|
|53| [What are custom elements?](#what-are-custom-elements)|
|54| [Do I need to bootstrap custom elements?](#do-i-need-to-bootstrap-custom-elements)|
|55| [Explain how custom elements works internally?](#explain-how-custom-elements-works-internally)|
|56| [How to transfer components to custom elements?](#how-to-transfer-components-to-custom-elements)|
|57| [What are the mapping rules between Angular component and custom element?](#what-are-the-mapping-rules-between-angular-component-and-custom-element)|
|58| [How do you define typings for custom elements?](#how-do-you-define-typings-for-custom-elements)|
|59| [What are dynamic components?](#what-are-dynamic-components)|
|60| [What are the various kinds of directives?](#what-are-the-various-kinds-of-directives)|
|61| [How do you create directives using CLI?](#how-do-you-create-directives-using-cli)|
|62| [Give an example for attribute directives?](#give-an-example-for-attribute-directives)|
|63| [What is Angular Router?](#what-is-angular-router)|
|64| [What is the purpose of base href tag?](#what-is-the-purpose-of-base-href-tag)|
|65| [What are the router imports?](#what-are-the-router-imports)|
|66| [What is router outlet?](#what-is-router-outlet)|
|67| [What are router links?](#what-are-router-links)|
|68| [What are active router links?](#what-are-active-router-links)|
|69| [What is router state?](#what-is-router-state)|
|70| [What are router events?](#what-are-router-events)|
|71| [What is activated route?](#what-is-activated-route)|
|72| [How do you define routes?](#how-do-you-define-routes)|
|73| [What is the purpose of Wildcard route?](#what-is-the-purpose-of-wildcard-route)|
|74| [Do I need a Routing Module always?](#do-i-need-a-routing-module-always)|
|75| [What is Angular Universal?](#what-is-angular-universal)|
|76| [What are different types of compilation in Angular?](#what-are-different-types-of-compilation-in-angular)|
|77| [What is JIT?](#what-is-jit)|
|78| [What is AOT?](#what-is-aot)|
|79| [Why do we need compilation process?](#why-do-we-need-compilation-process)|
|80| [What are the advantages with AOT?](#what-are-the-advantages-with-aot)|
|81| [What are the ways to control AOT compilation?](#what-are-the-ways-to-control-aot-compilation)|
|82| [What are the restrictions of metadata?](#what-are-the-restrictions-of-metadata)|
|83| [What are the three phases of AOT?](#what-are-the-three-phases-of-aot)|
|84| [Can I use arrow functions in AOT?](#can-i-use-arrow-functions-in-aot)|
|85| [What is the purpose of metadata json files?](#what-is-the-purpose-of-metadata-json-files)|
|86| [Can I use any javascript feature for expression syntax in AOT?](#can-i-use-any-javascript-feature-for-expression-syntax-in-aot)|
|87| [What is folding?](#what-is-folding)|
|88| [What are macros?](#what-are-macros)|
|89| [Give an example of few metadata errors?](#give-an-example-of-few-metadata-errors)|
|90| [What is metadata rewriting?](#what-is-metadata-rewriting)|
|91| [How do you provide configuration inheritance?](#how-do-you-provide-configuration-inheritance)|
|92| [How do you specify angular template compiler options?](#how-do-you-specify-angular-template-compiler-options)|
|93| [How do you enable binding expression validation?](#how-do-you-enable-binding-expression-validation)|
|94| [What is the purpose of any type cast function?](#what-is-the-purpose-of-any-type-cast-function)|
|95| [What is Non null type assertion operator?](#what-is-non-null-type-assertion-operator)|
|96| [What is type narrowing?](#what-is-type-narrowing)|
|97| [How do you describe various dependencies in angular application?](#how-do-you-describe-various-dependencies-in-angular-application)|
|98| [What is zone?](#what-is-zone)|
|99| [What is the purpose of common module?](#what-is-the-purpose-of-common-module)|
|100| [What is codelyzer?](#what-is-codelyzer)|
|101| [What is angular animation?](#what-is-angular-animation)|
|102| [What are the steps to use animation module?](#what-are-the-steps-to-use-animation-module)|
|103| [What is State function?](#what-is-state-function)|
|104| [What is Style function?](#what-is-style-function)|
|105| [What is the purpose of animate function?](#what-is-the-purpose-of-animate-function)|
|106| [What is transition function?](#what-is-transition-function)|
|107| [How to inject the dynamic script in angular?](#how-to-inject-the-dynamic-script-in-angular)|
|108| [What is a service worker and its role in Angular?](#what-is-a-service-worker-and-its-role-in-angular)|
|109| [What are the design goals of service workers?](#what-are-the-design-goals-of-service-workers)|
|110| [What are the differences between AngularJS and Angular with respect to dependency injection?](#what-are-the-differences-between-angularjs-and-angular-with-respect-to-dependency-injection)|
|111| [What is Angular Ivy?](#what-is-angular-ivy)|
|112| [What are the features included in ivy preview?](#what-are-the-features-included-in-ivy-preview)|
|113| [Can I use AOT compilation with Ivy?](#can-i-use-aot-compilation-with-ivy)|
|114| [What is Angular Language Service?](#what-is-angular-language-service)|
|115| [How do you install angular language service in the project?](#how-do-you-install-angular-language-service-in-the-project)|
|116| [Is there any editor support for Angular Language Service?](#is-there-any-editor-support-for-angular-language-service)|
|117| [Explain the features provided by Angular Language Service?](#explain-the-features-provided-by-angular-language-service)|
|118| [How do you add web workers in your application?](#how-do-you-add-web-workers-in-your-application)|
|119| [What are the limitations with web workers?](#what-are-the-limitations-with-web-workers)|
|120| [What is Angular CLI Builder?](#what-is-angular-cli-builder)|
|121| [What is a builder?](#what-is-a-builder)|
|122| [How do you invoke a builder?](#how-do-you-invoke-a-builder)|
|123| [How do you create app shell in Angular?](#how-do-you-create-app-shell-in-angular)|
|124| [What are the case types in Angular?](#what-are-the-case-types-in-angular)|
|125| [What are the class decorators in Angular?](#what-are-the-class-decorators-in-angular)|
|126| [What are class field decorators?](#what-are-class-field-decorators)|
|127| [What is declarable in Angular?](#what-is-declarable-in-angular)|
|128| [What are the restrictions on declarable classes?](#what-are-the-restrictions-on-declarable-classes)|
|129| [What is a DI token?](#what-is-a-di-token)|
|130| [What is Angular DSL?](#what-is-angular-dsl)|
|131| [What is an rxjs Subject?](#what-is-an-rxjs-Subject)|
|132| [What is Bazel tool?](#what-is-bazel-tool)|
|133| [What are the advantages of Bazel tool?](#what-are-the-advantages-of-bazel-tool)|
|134| [How do you use Bazel with Angular CLI?](#how-do-you-use-bazel-with-angular-cli)|
|135| [How do you run Bazel directly?](#how-do-you-run-bazel-directly)|
|136| [What is platform in Angular?](#what-is-platform-in-angular)|
|137| [What happens if I import the same module twice?](#what-happens-if-i-import-the-same-module-twice)|
|138| [How do you select an element with in a component template?](#how-do-you-select-an-element-with-in-a-component-template)|
|139| [How do you detect route change in Angular?](#how-do-you-detect-route-change-in-angular)|
|140| [How do you pass headers for HTTP client?](#how-do-you-pass-headers-for-http-client)|
|141| [What is the purpose of differential loading in CLI?](#what-is-the-purpose-of-differential-loading-in-cli)|
|142| [Is Angular supports dynamic imports?](#is-angular-supports-dynamic-imports)|
|143| [What is lazy loading?](#what-is-lazy-loading)|
|144| [What are workspace APIs?](#what-are-workspace-apis)|
|145| [How do you upgrade angular version?](#how-do-you-upgrade-angular-version)|
|146| [What is Angular Material?](#what-is-angular-material)|
|147| [How do you upgrade location service of angularjs?](#how-do-you-upgrade-location-service-of-angularjs)|
|148| [What is NgUpgrade?](#what-is-ngupgrade)|
|149| [How do you test Angular application using CLI?](#how-do-you-test-angular-application-using-cli)|
|150| [How to use polyfills in Angular application?](#how-to-use-polyfills-in-angular-application)|
|151| [What are the ways to trigger change detection in Angular?](#what-are-the-ways-to-trigger-change-detection-in-angular)|
|152| [What are the differences of various versions of Angular?](#what-are-the-differences-of-various-versions-of-angular)|
|153| [What are the security principles in angular?](#what-are-the-security-principles-in-angular)|
|154| [What is the reason to deprecate Web Tracing Framework?](#what-is-the-reason-to-deprecate-web-tracing-framework)|
|155| [What is the reason to deprecate web worker packages?](#what-is-the-reason-to-deprecate-web-worker-packages)|
|156| [How do you find angular CLI version?](#how-do-you-find-angular-cli-version)|
|157| [What is the browser support for Angular?](#what-is-the-browser-support-for-angular)|
|158| [What is schematic](#what-is-schematic)|
|159| [What is rule in Schematics?](#what-is-rule-in-schematics)|
|160| [What is Schematics CLI?](#what-is-schematics-cli)|
|161| [What are the best practices for security in angular?](#what-are-the-best-practices-for-security-in-angular)|
|162| [What is Angular security model for preventing XSS attacks?](#what-is-angular-security-model-for-preventing-xss-attacks)|
|163| [What is the role of template compiler for prevention of XSS attacks?](#what-is-the-role-of-template-compiler-for-prevention-of-xss-attacks)|
|164| [What are the various security contexts in Angular?](#what-are-the-various-security-contexts-in-Angular)|
|165| [What is Sanitization? Is angular supports it?](#what-is-sanitization?Is-angular-supports-it)|
|166| [What is the purpose of innerHTML?](#what-is-the-purpose-of-innerhtml)|
|167| [What is the difference between interpolated content and innerHTML?](#what-is-the-difference-between-interpolated-content-and-innerhtml)|
|168| [How do you prevent automatic sanitization?](#how-do-you-prevent-automatic-sanitization)|
|169| [Is safe to use direct DOM API methods in terms of security?](#is-safe-to-use-direct-dom-api-methods-in-terms-of-security)|
|170| [What is DOM sanitizer?](#what-is-dom-sanitizer)|
|171| [How do you support server side XSS protection in Angular application?](#how-do-you-support-server-side-xss-protection-in-angular-application)
|172| [Is angular prevents http level vulnerabilities?](#is-angular-prevents-http-level-vulnerabilities)|
|173| [What are Http Interceptors?](#what-are-http-interceptors)|
|174| [What are the applications of HTTP interceptors?](#what-are-the-applications-of-http-interceptors)|
|175| [Is multiple interceptors supported in Angular?](#is-multiple-interceptors-supported-in-angular)|
|176| [How can I use interceptor for an entire application?](#how-can-i-use-interceptor-for-an-entire-application)|
|177| [How does Angular simplifies Internationalization?](#how-does-angular-simplifies-internationalization)|
|178| [How do you manually register locale data?](#how-do-you-manually-register-locale-data)|
|179| [What are the four phases of template translation?](#what-are-the-four-phases-of-template-translation)|
|180| [What is the purpose of i18n attribute?](#what-is-the-purpose-of-i18n-attribute)|
|181| [What is the purpose of custom id?](#what-is-the-purpose-of-custom-id)|
|182| [What happens if the custom id is not unique?](#what-happens-if-the-custom-id-is-not-unique)|
|183| [Can I translate text without creating an element?](#can-i-translate-text-without-creating-an-element)|
|184| [How can I translate attribute?](#how-can-i-translate-attribute)|
|185| [List down the pluralization categories?](#list-down-the-pluralization-categories)|
|186| [What is select ICU expression?](#what-is-select-icu-expression)|
|187| [How do you report missing translations?](#how-do-you-report-missing-translations)|
|188| [How do you provide build configuration for multiple locales?](#how-do-you-provide-build-configuration-for-multiple-locales)|
|189| [What is an angular library?](#what-is-an-angular-library)|
|190| [What is AOT compiler?](#what-is-aot-compiler)|
|191| [How do you select an element in component template?](#how-do-you-select-an-element-in-component-template)|
|192| [What is TestBed?](#what-is-testbed)|
|193| [What is protractor?](#what-is-protractor)|
|194| [What is collection?](#what-is-collection)|
|195| [How do you create schematics for libraries?](#how-do-you-create-schematics-for-libraries)|
|196| [How do you use jquery in Angular?](#how-do-you-use-jquery-in-angular)|
|197| [What is the reason for No provider for HTTP exception?](#what-is-the-reason-for-no-provider-for-http-exception)|
|198| [What is router state?](#what-is-router-state)|
|199| [How can I use SASS in angular project?](#how-can-i-use-sass-in-angular-project)|
|200| [What is the purpose of hidden property?](#what-is-the-purpose-of-hidden-property)|
|201| [What is the difference between ngIf and hidden property?](#what-is-the-difference-between-ngif-and-hidden-property)|
|202| [What is slice pipe?](#what-is-slice-pipe)|
|203| [What is index property in ngFor directive?](#what-is-index-property-in-ngfor-directive)|
|204| [What is the purpose of ngFor trackBy?](#what-is-the-purpose-of-ngfor-trackby)|
|205| [What is the purpose of ngSwitch directive?](#what-is-the-purpose-of-ngswitch-directive)|
|206| [Is it possible to do aliasing for inputs and outputs?](#is-it-possible-to-do-aliasing-for-inputs-and-outputs)|
|207| [What is safe navigation operator?](#what-is-safe-navigation-operator)|
|208| [Is any special configuration required for Angular9?](#is-any-special-configuration-required-for-angular9)|
|209| [What are type safe TestBed API changes in Angular9?](#what-are-type-safe-testbed-api-changes-in-angular9)|
|210| [Is mandatory to pass static flag for ViewChild?](#is-mandatory-to-pass-static-flag-for-viewchild)|
|211| [What are the list of template expression operators?](#what-are-the-list-of-template-expression-operators)
|212| [What is the precedence between pipe and ternary operators?](#what-is-the-precedence-between-pipe-and-ternary-operators)
|213| [What is an entry component?](#what-is-an-entry-component)|
|214| [What is a bootstrapped component?](#what-is-a-bootstrapped-component)|
|215| [How do you manually bootstrap an application?](#how-do-you-manually-bootstrap-an-application)|
|216| [Is it necessary for bootstrapped component to be entry component?](#is-it-necessary-for-bootstrapped-component-to-be-entry-component)|
|217| [What is a routed entry component?](#what-is-a-routed-entry-component#)|
|218| [Why is not necessary to use entryComponents array every time?](#why-is-not-necessary-to-use-entrycomponents-array-every-time)|
|219| [Do I still need to use entryComponents array in Angular9?](#do-i-still-need-to-use-entrycomponents-array-in-angular9#)|
|220| [Is it all components generated in production build?](#is-it-all-components-generated-in-production-build)|
|221| [What is Angular compiler?](#what-is-angular-compiler)|
|222| [What is the role of ngModule metadata in compilation process?](#what-is-the-role-of-ngmodule-metadata-in-compilation-process)|
|223| [How does angular finds components, directives and pipes?](#how-does-angular-finds-components-directives-and-pipes)|
|224| [Give few examples for NgModules?](#give-few-examples-for-ngmodules)|
|225| [What are feature modules?](#what-are-feature-modules)|
|226| [What are the imported modules in CLI generated feature modules?](#what-are-the-imported-modules-in-cli-generated-feature-modules)|
|227| [What are the differences between ngmodule and javascript module?](#what-are-the-differences-between-ngmodule-and-javascript-module)|
|228| [What are the possible errors with declarations?](#what-are-the-possible-errors-with-declarations)|
|229| [What are the steps to use declaration elements?](#what-are-the-steps-to-use-declaration-elements)|
|230| [What happens if browserModule used in feature module?](#what-happens-if-browsermodule-used-in-feature-module)|
|231| [What are the types of feature modules?](#what-are-the-types-of-feature-modules)|
|232| [What is a provider?](#what-is-a-provider)|
|233| [What is the recommendation for provider scope?](#what-is-the-recommendation-for-provider-scope#)|
|234| [How do you restrict provider scope to a module?](#how-do-you-restrict-provider-scope-to-a-module)|
|235| [How do you provide a singleton service?](#how-do-you-provide-a-singleton-service)|
|236| [What are the different ways to remove duplicate service registration?](#what-are-the-different-ways-to-remove-duplicate-service-registration)|
|237| [How does forRoot method helpful to avoid duplicate router instances?](#how-does-forroot-method-helpful-to-avoid-duplicate-router-instances)|
|238| [What is a shared module?](#what-is-a-shared-module)|
|239| [Can I share services using modules?](#can-i-share-services-using-modules)|
|240| [How do you get current direction for locales??](#how-do-you-get-current-direction-for-locales)|
|241| [What is ngcc?](#what-is-ngcc)|
|242| [What classes should not be added to declarations?](#what-classes-should-not-be-added-to-declarations)|
|243| [What is ngzone?](#what-is-ngzone)|
|244| [What is NoopZone?](#what-is-noopzone)|
|245| [How do you create displayBlock components?](#how-do-you-create-displayblock-components)|
|246| [What are the possible data change scenarios for change detection?](#what-are-the-possible-data-change-scenarios-for-change-detection)|
|247| [What is a zone context?](#what-is-a-zone-context)|
|248| [What are the lifecycle hooks of a zone?](#what-are-the-lifecycle-hooks-of-a-zone)|
|249| [Which are the methods of NgZone used to control change detection?](#which-are-the-methods-of-ngzone-used-to-control-change-detection)|
|250| [How do you change the settings of zonejs?](#how-do-you-change-the-settings-of-zonejs)|
|251| [How do you trigger an animation?](#how-do-you-trigger-an-animation)|
|252| [How do you configure injectors with providers at different levels?](#how-do-you-configure-injectors-with-providers-at-different-levels)|
|253| [Is it mandatory to use injectable on every service class?](#is-it-mandatory-to-use-injectable-on-every-service-class)|
|254| [What is an optional dependency?](#what-is-an-optional-dependency)|
|255| [What are the types of injector hierarchies?](#what-are-the-types-of-injector-hierarchies)|
|256| [What are reactive forms?](#what-are-reactive-forms)|
|257| [What are dynamic forms?](#what-are-dynamic-forms)|
|258| [What are template driven forms?](#what-are-template-driven-forms)|
|259| [What are the differences between reactive forms and template driven forms?](#what-are-the-differences-between-reactive-forms-and-template-driven-forms)|
|260| [What are the different ways to group form controls?](#what-are-the-different-ways-to-group-form-controls)|
|261| [How do you update specific properties of a form model?](#how-do-you-update-specific-properties-of-a-form-model)|
|262| [What is the purpose of FormBuilder?](#what-is-the-purpose-of-formbuilder)|
|263| [How do you verify the model changes in forms?](#how-do-you-verify-the-model-changes-in-forms)|
|264| [What are the state CSS classes provided by ngModel?](#what-are-the-state-css-classes-provided-by-ngmodel)|
|265| [How do you reset the form?](#how-do-you-reset-the-form)|
|266| [What are the types of validator functions?](#what-are-the-types-of-validator-functions)|
|267| [Can you give an example of built-in validators?](#can-you-give-an-example-of-built-in-validators)|
|268| [How do you optimize the performance of async validators?](#how-do-you-optimize-the-performance-of-async-validators)|
|269| [How to set ngFor and ngIf on the same element?](#how-to-set-ngfor-and-ngif-on-the-same-element)|
|270| [What is host property in css?](#what-is-host-property-in-css)|
|271| [How do you get the current route?](#how-do-you-get-the-current-route)|
|272| [What is Component Test Harnesses?](#what-is-component-test-harnesses)|
|273| [What is the benefit of Automatic Inlining of Fonts?](#what-is-the-benefit-of-automatic-inlining-of-fonts)|
|274| [What is content projection?](#what-is-content-projection)|
|275| [What is ng-content and its purpose?](#what-is-ng-content-and-its-purpose)|
|276| [What is standalone component?](#what-is-standalone-component)|
|277| [How to create a standalone component uing CLI command?](#how-to-create-a-standalone-component-uing-cli-command)
|278| [How to create a standalone component manually?](#how-to-create-a-standalone-component-manually)
|279| [What is hydration ?](#what-is-hydration)
|279| [](#)
1. ### What is Angular Framework?
Angular is a **TypeScript-based open-source** front-end platform that makes it easy to build web, mobile and desktop applications. The major features of this framework include declarative templates, dependency injection, end to end tooling which ease application development.
**[⬆ Back to Top](#table-of-contents)**
2. ### What is the difference between AngularJS and Angular?
Angular is a completely revived component-based framework in which an application is a tree of individual components.
Here are some of the major differences in tabular format:-
| AngularJS | Angular |
|---- | ---------
| It is based on MVC architecture| This is based on Service/Controller|
| It uses JavaScript to build the application| Uses TypeScript to build the application|
| Based on controllers concept| This is a component based UI approach|
| No support for mobile platforms| Fully supports mobile platforms|
| Difficult to build SEO friendly application| Ease to build SEO friendly applications|
**[⬆ Back to Top](#table-of-contents)**
3. ### What is TypeScript?
TypeScript is a strongly typed superset of JavaScript created by Microsoft that adds optional types, classes, async/await and many other features, and compiles to plain JavaScript. Angular is written entirely in TypeScript as a primary language.
You can install TypeScript globally as
```cmd
npm install -g typescript
```
Let's see a simple example of TypeScript usage:-
```typescript
function greeter(person: string) {
return "Hello, " + person;
}
let user = "Sudheer";
document.body.innerHTML = greeter(user);
```
The greeter method allows only string type as argument.
**[⬆ Back to Top](#table-of-contents)**
4. ### Write a pictorial diagram of Angular architecture?
The main building blocks of an Angular application are shown in the diagram below:-
**[⬆ Back to Top](#table-of-contents)**
5. ### What are the key components of Angular?
Angular has the key components below,
1. **Component:** These are the basic building blocks of an Angular application to control HTML views.
2. **Modules:** An Angular module is a set of angular basic building blocks like components, directives, services etc. An application is divided into logical pieces and each piece of code is called as "module" which perform a single task.
3. **Templates:** These represent the views of an Angular application.
4. **Services:** Are used to create components which can be shared across the entire application.
5. **Metadata:** This can be used to add more data to an Angular class.
**[⬆ Back to Top](#table-of-contents)**
6. ### What are directives?
Directives add behaviour to an existing DOM element or an existing component instance.
```typescript
import { Directive, ElementRef, Input } from '@angular/core';
@Directive({ selector: '[myHighlight]' })
export class HighlightDirective {
constructor(el: ElementRef) {
el.nativeElement.style.backgroundColor = 'yellow';
}
}
```
Now this directive extends HTML element behavior with a yellow background as below
```html
<p myHighlight>Highlight me!</p>
```
**[⬆ Back to Top](#table-of-contents)**
7. ### What are components?
Components are the most basic UI building block of an Angular app, which form a tree of Angular components. These components are a subset of directives. Unlike directives, components always have a template, and only one component can be instantiated per element in a template.
Let's see a simple example of Angular component
```typescript
import { Component } from '@angular/core';
@Component ({
selector: 'my-app',
template: ` <div>
<h1>{{title}}</h1>
<div>Learn Angular6 with examples</div>
</div> `,
})
export class AppComponent {
title: string = 'Welcome to Angular world';
}
```
**[⬆ Back to Top](#table-of-contents)**
8. ### What are the differences between Component and Directive?
In a short note, A component(@component) is a directive-with-a-template.
Some of the major differences are mentioned in a tabular form
| Component | Directive |
|---- | ---------
| To register a component we use @Component meta-data annotation | To register a directive we use @Directive meta-data annotation |
| Components are typically used to create UI widgets| Directives are used to add behavior to an existing DOM element |
| Component is used to break down the application into smaller components| Directive is used to design re-usable components|
| Only one component can be present per DOM element | Many directives can be used per DOM element |
| @View decorator or templateurl/template are mandatory | Directive doesn't use View|
**[⬆ Back to Top](#table-of-contents)**
9. ### What is a template?
A template is a HTML view where you can display data by binding controls to properties of an Angular component. You can store your component's template in one of two places. You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator's templateUrl property.
**Using inline template with template syntax,**
```typescript
import { Component } from '@angular/core';
@Component ({
selector: 'my-app',
template: '
<div>
<h1>{{title}}</h1>
<div>Learn Angular</div>
</div>
'
})
export class AppComponent {
title: string = 'Hello World';
}
```
**Using separate template file such as app.component.html**
```typescript
import { Component } from '@angular/core';
@Component ({
selector: 'my-app',
templateUrl: 'app/app.component.html'
})
export class AppComponent {
title: string = 'Hello World';
}
```
**[⬆ Back to Top](#table-of-contents)**
10. ### What is a module?
Modules are logical boundaries in your application and the application is divided into separate modules to separate the functionality of your application.
Lets take an example of **app.module.ts** root module declared with **@NgModule** decorator as below,
```typescript
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
@NgModule ({
imports: [ BrowserModule ],
declarations: [ AppComponent ],
bootstrap: [ AppComponent ],
providers: []
})
export class AppModule { }
```
The NgModule decorator has five important (among all) options:
1. The imports option is used to import other dependent modules. The BrowserModule is required by default for any web based angular application.
2. The declarations option is used to define components in the respective module.
3. The bootstrap option tells Angular which Component to bootstrap in the application.
4. The providers option is used to configure a set of injectable objects that are available in the injector of this module.
5. The entryComponents option is a set of components dynamically loaded into the view.
**[⬆ Back to Top](#table-of-contents)**
11. ### What are lifecycle hooks available?
Angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application.
The representation of lifecycle in pictorial representation as follows,
The description of each lifecycle method is as below,
1. **ngOnChanges:** When the value of a data bound property changes, then this method is called.
2. **ngOnInit:** This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens.
3. **ngDoCheck:** This is for the detection and to act on changes that Angular can't or won't detect on its own.
4. **ngAfterContentInit:** This is called in response after Angular projects external content into the component's view.
5. **ngAfterContentChecked:** This is called in response after Angular checks the content projected into the component.
6. **ngAfterViewInit:** This is called in response after Angular initializes the component's views and child views.
7. **ngAfterViewChecked:** This is called in response after Angular checks the component's views and child views.
8. **ngOnDestroy:** This is the cleanup phase just before Angular destroys the directive/component.
**[⬆ Back to Top](#table-of-contents)**
12. ### What is a data binding?
Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data. There are four forms of data binding(divided as 3 categories) which differ in the way the data is flowing.
1. **From the Component to the DOM:**
**Interpolation:** {{ value }}: Adds the value of a property from the component
```html
<li>Name: {{ user.name }}</li>
<li>Address: {{ user.address }}</li>
```
**Property binding:** [property]=”value”: The value is passed from the component to the specified property or simple HTML attribute
```html
<input type="email" [value]="user.email">
```
2. **From the DOM to the Component:**
**Event binding: (event)=”function”:** When a specific DOM event happens (eg.: click, change, keyup), call the specified method in the component
```html
<button (click)="logout()"></button>
```
3. **Two-way binding:**
**Two-way data binding:** [(ngModel)]=”value”: Two-way data binding allows to have the data flow both ways. For example, in the below code snippet, both the email DOM input and component email property are in sync
```html
<input type="email" [(ngModel)]="user.email">
```
**[⬆ Back to Top](#table-of-contents)**
13. ### What is metadata?
Metadata is used to decorate a class so that it can configure the expected behavior of the class. The metadata is represented by decorators
1. **Class decorators**, e.g. @Component and @NgModule
```typescript
import { NgModule, Component } from '@angular/core';
@Component({
selector: 'my-component',
template: '<div>Class decorator</div>',
})
export class MyComponent {
constructor() {
console.log('Hey I am a component!');
}
}
@NgModule({
imports: [],
declarations: [],
})
export class MyModule {
constructor() {
console.log('Hey I am a module!');
}
}
```
2. **Property decorators** Used for properties inside classes, e.g. @Input and @Output
```typescript
import { Component, Input } from '@angular/core';
@Component({
selector: 'my-component',
template: '<div>Property decorator</div>'
})
export class MyComponent {
@Input()
title: string;
}
```
3. **Method decorators** Used for methods inside classes, e.g. @HostListener
```typescript
import { Component, HostListener } from '@angular/core';
@Component({
selector: 'my-component',
template: '<div>Method decorator</div>'
})
export class MyComponent {
@HostListener('click', ['$event'])
onHostClick(event: Event) {
// clicked, `event` available
}
}
```
4. **Parameter decorators** Used for parameters inside class constructors, e.g. @Inject, @Optional
```typescript
import { Component, Inject } from '@angular/core';
import { MyService } from './my-service';
@Component({
selector: 'my-component',
template: '<div>Parameter decorator</div>'
})
export class MyComponent {
constructor(@Inject(MyService) myService) {
console.log(myService); // MyService
}
}
```
**[⬆ Back to Top](#table-of-contents)**
14. ### What is angular CLI?
Angular CLI(**Command Line Interface**) is a command line interface to scaffold and build angular apps using nodejs style (commonJs) modules.
You need to install using below npm command,
```
npm install @angular/cli@latest
```
Below are the list of few commands, which will come handy while creating angular projects
1. **Creating New Project:** ng new <project-name>
2. **Generating Components, Directives & Services:** ng generate/g <feature-name>
The different types of commands would be,
* ng generate class my-new-class: add a class to your application
* ng generate component my-new-component: add a component to your application
* ng generate directive my-new-directive: add a directive to your application
* ng generate enum my-new-enum: add an enum to your application
* ng generate module my-new-module: add a module to your application
* ng generate pipe my-new-pipe: add a pipe to your application
* ng generate service my-new-service: add a service to your application
3. **Running the Project:** ng serve
**[⬆ Back to Top](#table-of-contents)**
15. ### What is the difference between constructor and ngOnInit?
The **Constructor** is a default method of the class that is executed when the class is instantiated and ensures proper initialisation of fields in the class and its subclasses. Angular, or better Dependency Injector (DI), analyses the constructor parameters and when it creates a new instance by calling new MyClass() it tries to find providers that match the types of the constructor parameters, resolves them and passes them to the constructor.
**ngOnInit** is a life cycle hook called by Angular to indicate that Angular is done creating the component.
Mostly we use ngOnInit for all the initialization/declaration and avoid stuff to work in the constructor. The constructor should only be used to initialize class members but shouldn't do actual "work".
So you should use constructor() to setup Dependency Injection and not much else. ngOnInit() is better place to "start" - it's where/when components' bindings are resolved.
```typescript
export class App implements OnInit{
constructor(private myService: MyService){
//called first time before the ngOnInit()
}
ngOnInit(){
//called after the constructor and called after the first ngOnChanges()
//e.g. http call...
}
}
```
**[⬆ Back to Top](#table-of-contents)**
16. ### What is a service?
A service is used when a common functionality needs to be provided to various modules. Services allow for greater separation of concerns for your application and better modularity by allowing you to extract common functionality out of components.
Let's create a repoService which can be used across components,
```typescript
import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
@Injectable({ // The Injectable decorator is required for dependency injection to work
// providedIn option registers the service with a specific NgModule
providedIn: 'root', // This declares the service with the root app (AppModule)
})
export class RepoService{
constructor(private http: Http){
}
fetchAll(){
return this.http.get('https://api.github.com/repositories');
}
}
```
The above service uses Http service as a dependency.
**[⬆ Back to Top](#table-of-contents)**
17. ### What is dependency injection in Angular?
Dependency injection (DI), is an important application design pattern in which a class asks for dependencies from external sources rather than creating them itself. Angular comes with its own dependency injection framework for resolving dependencies( services or objects that a class needs to perform its function).So you can have your services depend on other services throughout your application.
**[⬆ Back to Top](#table-of-contents)**
18. ### How is Dependency Hierarchy formed?
Injectors in Angular have rules that can be leveraged to achieve the desired visibility of injectables in your applications. By understanding these rules, you can determine in which NgModule, Component, or Directive you should declare a provider.
#### Angular has two injector hierarchies:
#### Module injector
When angular starts, it creates a root injector where the services will be registered, these are provided via injectable annotation. All services provided in the `ng-model` property are called providers (if those modules are not lazy-loaded).
Angular recursively goes through all models which are being used in the application and creates instances for provided services in the root injector. If you provide some service in an eagerly-loaded model, the service will be added to the root injector, which makes it available across the whole application.
#### Platform Module
During application bootstrapping angular creates a few more injectors, above the root injector goes the platform injector, this one is created by the platform browser dynamic function inside the `main.ts` file, and it provides some platform-specific features like `DomSanitizer`.
#### NullInjector()
At the very top, the next parent injector in the hierarchy is the `NullInjector()`.The responsibility of this injector is to throw the error if something tries to find dependencies there, unless you've used `@Optional()` because ultimately, everything ends at the `NullInjector()` and it returns an error or, in the case of `@Optional()`, `null`.
#### ElementInjector
Angular creates `ElementInjector` hierarchies implicitly for each DOM element. `ElementInjector` injector is being created for any tag that matches the angular component, or any tag on which directive is applied, and you can configure it in component and directive annotations inside the provider's property, thus, it creates its own hierarchy likewise the upper one.
**[⬆ Back to Top](#table-of-contents)**
19. ### What is the purpose of async pipe?
The AsyncPipe subscribes to an observable or promise and returns the latest value it has emitted. When a new value is emitted, the pipe marks the component to be checked for changes.
Let's take a time observable which continuously updates the view for every 2 seconds with the current time.
```typescript
@Component({
selector: 'async-observable-pipe',
template: `<div><code>observable|async</code>:
Time: {{ time | async }}</div>`
})
export class AsyncObservablePipeComponent {
time: Observable<string>;
constructor() {
this.time = new Observable((observer) => {
setInterval(() => {
observer.next(new Date().toString());
}, 2000);
});
}
}
```
**[⬆ Back to Top](#table-of-contents)**
20. ### What is the option to choose between inline and external template file?
You can store your component's template in one of two places. You can define it inline using the **template** property, or you can define the template in a separate HTML file and link to it in the component metadata using the **@Component** decorator's **templateUrl** property.
The choice between inline and separate HTML is a matter of taste, circumstances, and organization policy. But normally we use inline template for small portion of code and external template file for bigger views. By default, the Angular CLI generates components with a template file. But you can override that with the below command,
```
ng generate component hero -it
```
**[⬆ Back to Top](#table-of-contents)**
21. ### What is the purpose of `*ngFor` directive?
We use Angular `*ngFor` directive in the template to display each item in the list. For example, here we can iterate over a list of users:
```html
<li *ngFor="let user of users">
{{ user }}
</li>
```
The user variable in the `*ngFor` double-quoted instruction is a **template input variable**.
**[⬆ Back to Top](#table-of-contents)**
22. ### What is the purpose of `*ngIf` directive?
Sometimes an app needs to display a view or a portion of a view only under specific circumstances. The Angular `*ngIf` directive inserts or removes an element based on a truthy/falsy condition. Let's take an example to display a message if the user age is more than 18:
```html
<p *ngIf="user.age > 18">You are not eligible for student pass!</p>
```
**Note:** Angular isn't showing and hiding the message. It is adding and removing the paragraph element from the DOM. That improves performance, especially in the larger projects with many data bindings.
**[⬆ Back to Top](#table-of-contents)**
23. ### What happens if you use script tag inside template?
Angular recognizes the value as unsafe and automatically sanitizes it, which removes the `script` tag but keeps safe content such as the text content of the `script` tag. This way it eliminates the risk of script injection attacks. If you still use it then it will be ignored and a warning appears in the browser console.
Let's take an example of innerHtml property binding which causes XSS vulnerability,
```typescript
export class InnerHtmlBindingComponent {
// For example, a user/attacker-controlled value from a URL.
htmlSnippet = 'Template <script>alert("0wned")</script> <b>Syntax</b>';
}
```
**[⬆ Back to Top](#table-of-contents)**
24. ### What is interpolation?
Interpolation is a special syntax that Angular converts into property binding. It’s a convenient alternative to property binding. It is represented by double curly braces({{}}). The text between the braces is often the name of a component property. Angular replaces that name with the string value of the corresponding component property.
Let's take an example,
```html
<h3>
{{title}}
<img src="{{url}}" style="height:30px">
</h3>
```
In the example above, Angular evaluates the title and url properties and fills in the blanks, first displaying a bold application title and then a URL.
**[⬆ Back to Top](#table-of-contents)**
25. ### What are template expressions?
A template expression produces a value similar to any Javascript expression. Angular executes the expression and assigns it to a property of a binding target; the target might be an HTML element, a component, or a directive. In the property binding, a template expression appears in quotes to the right of the = symbol as in `[property]="expression"`.
In interpolation syntax, the template expression is surrounded by double curly braces. For example, in the below interpolation, the template expression is `{{username}}`,
```html
<h3>{{username}}, welcome to Angular</h3>
```
The below javascript expressions are prohibited in template expression
1. assignments (=, +=, -=, ...)
2. new
3. chaining expressions with ; or ,
4. increment and decrement operators (++ and --)
----------------------------------
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26. ### What are template statements?
A template statement responds to an event raised by a binding target such as an element, component, or directive. The template statements appear in quotes to the right of the = symbol like `(event)="statement"`.
Let's take an example of button click event's statement
```html
<button (click)="editProfile()">Edit Profile</button>
```
In the above expression, editProfile is a template statement. The below JavaScript syntax expressions are not allowed.
1. new
2. increment and decrement operators, ++ and --
3. operator assignment, such as += and -=
4. the bitwise operators | and &
5. the template expression operators
--------------------------------------
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27. ### How do you categorize data binding types?
Binding types can be grouped into three categories distinguished by the direction of data flow. They are listed as below,
1. From the source-to-view
2. From view-to-source
3. View-to-source-to-view
The possible binding syntax can be tabularized as below,
| Data direction | Syntax | Type |
|---- | --------- | ---- |
| From the source-to-view(One-way) | 1. {{expression}} 2. [target]="expression" 3. bind-target="expression" | Interpolation, Property, Attribute, Class, Style|
| From view-to-source(One-way) | 1. (target)="statement" 2. on-target="statement" | Event |
| View-to-source-to-view(Two-way)| 1. [(target)]="expression" 2. bindon-target="expression"| Two-way |
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28. ### What are pipes?
Pipes are simple functions that use [template expressions](#what-are-template-expressions) to accept data as input and transform it into a desired output. For example, let us take a pipe to transform a component's birthday property into a human-friendly date using **date** pipe.
```javascript
import { Component } from '@angular/core';
@Component({
selector: 'app-birthday',
template: `<p>Birthday is {{ birthday | date }}</p>`
})
export class BirthdayComponent {
birthday = new Date(1987, 6, 18); // June 18, 1987
}
```
**[⬆ Back to Top](#table-of-contents)**
29. ### What is a parameterized pipe?
A pipe can accept any number of optional parameters to fine-tune its output. The parameterized pipe can be created by declaring the pipe name with a colon ( : ) and then the parameter value. If the pipe accepts multiple parameters, separate the values with colons. Let's take a birthday example with a particular format(dd/MM/yyyy):
```javascript
import { Component } from '@angular/core';
@Component({
selector: 'app-birthday',
template: `<p>Birthday is {{ birthday | date:'dd/MM/yyyy'}}</p>` // 18/06/1987
})
export class BirthdayComponent {
birthday = new Date(1987, 6, 18);
}
```
**Note:** The parameter value can be any valid template expression, such as a string literal or a component property.
**[⬆ Back to Top](#table-of-contents)**
30. ### How do you chain pipes?
You can chain pipes together in potentially useful combinations as per the needs. Let's take a birthday property which uses date pipe(along with parameter) and uppercase pipes as below
```javascript
import { Component } from '@angular/core';
@Component({
selector: 'app-birthday',
template: `<p>Birthday is {{ birthday | date:'fullDate' | uppercase}} </p>` // THURSDAY, JUNE 18, 1987
})
export class BirthdayComponent {
birthday = new Date(1987, 6, 18);
}
```
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31. ### What is a custom pipe?
Apart from built-in pipes, you can write your own custom pipe with the below key characteristics:
1. A pipe is a class decorated with pipe metadata `@Pipe` decorator, which you import from the core Angular library
For example,
```javascript
@Pipe({name: 'myCustomPipe'})
```
2. The pipe class implements the **PipeTransform** interface's transform method that accepts an input value followed by optional parameters and returns the transformed value.
The structure of `PipeTransform` would be as below,
```javascript
interface PipeTransform {
transform(value: any, ...args: any[]): any
}
```
3. The `@Pipe` decorator allows you to define the pipe name that you'll use within template expressions. It must be a valid JavaScript identifier.
```javascript
template: `{{someInputValue | myCustomPipe: someOtherValue}}`
```
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32. ### Give an example of custom pipe?
You can create custom reusable pipes for the transformation of existing value. For example, let us create a custom pipe for finding file size based on an extension,
```javascript
import { Pipe, PipeTransform } from '@angular/core';
@Pipe({name: 'customFileSizePipe'})
export class FileSizePipe implements PipeTransform {
transform(size: number, extension: string = 'MB'): string {
return (size / (1024 * 1024)).toFixed(2) + extension;
}
}
```
Now you can use the above pipe in template expression as below,
```javascript
template: `
<h2>Find the size of a file</h2>
<p>Size: {{288966 | customFileSizePipe: 'GB'}}</p>
`
```
**[⬆ Back to Top](#table-of-contents)**
33. ### What is the difference between pure and impure pipe?
A pure pipe is only called when Angular detects a change in the value or the parameters passed to a pipe. For example, any changes to a primitive input value (String, Number, Boolean, Symbol) or a changed object reference (Date, Array, Function, Object). An impure pipe is called for every change detection cycle no matter whether the value or parameters changes. i.e, An impure pipe is called often, as often as every keystroke or mouse-move.
**[⬆ Back to Top](#table-of-contents)**
34. ### What is a bootstrapping module?
Every application has at least one Angular module, the root module that you bootstrap to launch the application is called as bootstrapping module. It is commonly known as `AppModule`. The default structure of `AppModule` generated by AngularCLI would be as follows:
```javascript
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';
import { AppComponent } from './app.component';
/* the AppModule class with the @NgModule decorator */
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
FormsModule,
HttpClientModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }
```
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35. ### What are observables?
Observables are declarative which provide support for passing messages between publishers and subscribers in your application. They are mainly used for event handling, asynchronous programming, and handling multiple values. In this case, you define a function for publishing values, but it is not executed until a consumer subscribes to it. The subscribed consumer then receives notifications until the function completes, or until they unsubscribe.
**[⬆ Back to Top](#table-of-contents)**
36. ### What is HttpClient and its benefits?
Most of the Front-end applications communicate with backend services over `HTTP` protocol using either `XMLHttpRequest` interface or the `fetch()` API. Angular provides a simplified client HTTP API known as `HttpClient` which is based on top of `XMLHttpRequest` interface. This client is available from `@angular/common/http` package.
You can import in your root module as below:
```javascript
import { HttpClientModule } from '@angular/common/http';
```
The major advantages of HttpClient can be listed as below,
1. Contains testability features
2. Provides typed request and response objects
3. Intercept request and response
4. Supports Observable APIs
5. Supports streamlined error handling
**[⬆ Back to Top](#table-of-contents)**
37. ### Explain on how to use `HttpClient` with an example?
Below are the steps need to be followed for the usage of `HttpClient`.
1. Import `HttpClient` into root module:
```javascript
import { HttpClientModule } from '@angular/common/http';
@NgModule({
imports: [
BrowserModule,
// import HttpClientModule after BrowserModule.
HttpClientModule,
],
......
})
export class AppModule {}
```
2. Inject the `HttpClient` into the application:
Let's create a userProfileService(`userprofile.service.ts`) as an example. It also defines get method of `HttpClient`:
```javascript
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
const userProfileUrl: string = 'assets/data/profile.json';
@Injectable()
export class UserProfileService {
constructor(private http: HttpClient) { }
getUserProfile() {
return this.http.get(this.userProfileUrl);
}
}
```
3. Create a component for subscribing service:
Let's create a component called UserProfileComponent(`userprofile.component.ts`), which injects `UserProfileService` and invokes the service method:
```javascript
fetchUserProfile() {
this.userProfileService.getUserProfile()
.subscribe((data: User) => this.user = {
id: data['userId'],
name: data['firstName'],
city: data['city']
});
}
```
Since the above service method returns an Observable which needs to be subscribed in the component.
**[⬆ Back to Top](#table-of-contents)**
38. ### How can you read full response?
The response body doesn't or may not return full response data because sometimes servers also return special headers or status code, which are important for the application workflow. In order to get the full response, you should use `observe` option from `HttpClient`:
```javascript
getUserResponse(): Observable<HttpResponse<User>> {
return this.http.get<User>(
this.userUrl, { observe: 'response' });
}
```
Now `HttpClient.get()` method returns an Observable of typed `HttpResponse` rather than just the `JSON` data.
**[⬆ Back to Top](#table-of-contents)**
39. ### How do you perform Error handling?
If the request fails on the server or fails to reach the server due to network issues, then `HttpClient` will return an error object instead of a successful reponse. In this case, you need to handle in the component by passing `error` object as a second callback to `subscribe()` method.
Let's see how it can be handled in the component with an example,
```javascript
fetchUser() {
this.userService.getProfile()
.subscribe(
(data: User) => this.userProfile = { ...data }, // success path
error => this.error = error // error path
);
}
```
It is always a good idea to give the user some meaningful feedback instead of displaying the raw error object returned from `HttpClient`.
**[⬆ Back to Top](#table-of-contents)**
40. ### What is RxJS?
RxJS is a library for composing asynchronous and callback-based code in a functional, reactive style using Observables. Many APIs such as HttpClient produce and consume RxJS Observables and also uses operators for processing observables.
For example, you can import observables and operators for using HttpClient as below,
```javascript
import { Observable, throwError } from 'rxjs';
import { catchError, retry } from 'rxjs/operators';
```
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41. ### What is subscribing?
An Observable instance begins publishing values only when someone subscribes to it. So you need to subscribe by calling the `subscribe()` method of the instance, passing an observer object to receive the notifications.
Let's take an example of creating and subscribing to a simple observable, with an observer that logs the received message to the console.
```javascript
// Creates an observable sequence of 5 integers, starting from 1
const source = range(1, 5);
// Create observer object
const myObserver = {
next: x => console.log('Observer got a next value: ' + x),
error: err => console.error('Observer got an error: ' + err),
complete: () => console.log('Observer got a complete notification'),
};
// Execute with the observer object and Prints out each item
source.subscribe(myObserver);
// => Observer got a next value: 1
// => Observer got a next value: 2
// => Observer got a next value: 3
// => Observer got a next value: 4
// => Observer got a next value: 5
// => Observer got a complete notification
```
**[⬆ Back to Top](#table-of-contents)**
42. ### What is an observable?
An Observable is a unique Object similar to a Promise that can help manage async code. Observables are not part of the JavaScript language so we need to rely on a popular Observable library called RxJS.
The observables are created using new keyword.
Let see the simple example of observable,
```javascript
import { Observable } from 'rxjs';
const observable = new Observable(observer => {
setTimeout(() => {
observer.next('Hello from a Observable!');
}, 2000);
});
```
**[⬆ Back to Top](#table-of-contents)**
43. ### What is an observer?
Observer is an interface for a consumer of push-based notifications delivered by an Observable. It has below structure,
```javascript
interface Observer<T> {
closed?: boolean;
next: (value: T) => void;
error: (err: any) => void;
complete: () => void;
}
```
A handler that implements the Observer interface for receiving observable notifications will be passed as a parameter for observable as below,
```javascript
myObservable.subscribe(myObserver);
```
**Note:** If you don't supply a handler for a notification type, the observer ignores notifications of that type.
**[⬆ Back to Top](#table-of-contents)**
44. ### What is the difference between promise and observable?
Below are the list of differences between promise and observable:
| Observable | Promise |
|---- | --------- |
| Declarative: Computation does not start until subscription, so they can run whenever you need the result | Executes immediately on creation|
| Provides multiple values over time | Provides only one |
| Subscribe method is used for error handling that facilitates centralized and predictable error handling | Push errors to the child promises |
| Provides chaining and subscription to handle complex applications | Uses only `.then()` clause |
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45. ### What is multicasting?
Multi-casting is the practice of broadcasting to a list of multiple subscribers in a single execution.
Let's demonstrate the multi-casting feature:
```javascript
var source = Rx.Observable.from([1, 2, 3]);
var subject = new Rx.Subject();
var multicasted = source.multicast(subject);
// These are, under the hood, `subject.subscribe({...})`:
multicasted.subscribe({
next: (v) => console.log('observerA: ' + v)
});
multicasted.subscribe({
next: (v) => console.log('observerB: ' + v)
});
// This is, under the hood, `s
```
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46. ### How do you perform error handling in observables?
You can handle errors by specifying an **error callback** on the observer instead of relying on `try`/`catch`, which are ineffective in asynchronous environment.
For example, you can define error callback as below,
```javascript
myObservable.subscribe({
next(num) { console.log('Next num: ' + num)},
error(err) { console.log('Received an errror: ' + err)}
});
```
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47. ### What is the shorthand notation for subscribe method?
The `subscribe()` method can accept callback function definitions in line, for `next`, `error`, and `complete` handlers. It is known as shorthand notation or Subscribe method with positional arguments.
For example, you can define subscribe method as below,
```javascript
myObservable.subscribe(
x => console.log('Observer got a next value: ' + x),
err => console.error('Observer got an error: ' + err),
() => console.log('Observer got a complete notification')
);
```
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48. ### What are the utility functions provided by RxJS?
The RxJS library also provides below utility functions for creating and working with observables.
1. Converting existing code for async operations into observables
2. Iterating through the values in a stream
3. Mapping values to different types
4. Filtering streams
5. Composing multiple streams
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49. ### What are observable creation functions?
RxJS provides creation functions for the process of creating observables from promises, events, timers and Ajax requests. Let us explain each of them with an example:
1. Create an observable from a promise
```javascript
import { from } from 'rxjs'; // from function
const data = from(fetch('/api/endpoint')); //Created from Promise
data.subscribe({
next(response) { console.log(response); },
error(err) { console.error('Error: ' + err); },
complete() { console.log('Completed'); }
});
```
2. Create an observable that creates an AJAX request
```javascript
import { ajax } from 'rxjs/ajax'; // ajax function
const apiData = ajax('/api/data'); // Created from AJAX request
// Subscribe to create the request
apiData.subscribe(res => console.log(res.status, res.response));
```
3. Create an observable from a counter
```javascript
import { interval } from 'rxjs'; // interval function
const secondsCounter = interval(1000); // Created from Counter value
secondsCounter.subscribe(n =>
console.log(`Counter value: ${n}`));
```
4. Create an observable from an event
```javascript
import { fromEvent } from 'rxjs';
const el = document.getElementById('custom-element');
const mouseMoves = fromEvent(el, 'mousemove');
const subscription = mouseMoves.subscribe((e: MouseEvent) => {
console.log(`Coordnitaes of mouse pointer: ${e.clientX} * ${e.clientY}`);
});
```
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50. ### What will happen if you do not supply handler for the observer?
Usually, an observer object can define any combination of `next`, `error`, and `complete` notification type handlers. If you don't supply a handler for a notification type, the observer just ignores notifications of that type.
**[⬆ Back to Top](#table-of-contents)**
51. ### What are Angular elements?
Angular elements are Angular components packaged as **custom elements** (a web standard for defining new HTML elements in a framework-agnostic way). Angular Elements host an Angular component, providing a bridge between the data and the logic defined in the component and the standard DOM APIs, thus, providing a way to use Angular components in `non-Angular environments`.
**[⬆ Back to Top](#table-of-contents)**
52. ### What is the browser support of Angular Elements?
Since Angular elements are packaged as custom elements the browser support of angular elements is same as custom elements support.
This feature is is currently supported natively in a number of browsers and pending for other browsers.
| Browser | Angular Element Support |
|---- | --------- |
| Chrome | Natively supported|
| Opera | Natively supported |
| Safari| Natively supported |
| Firefox | Natively supported from 63 version onwards. You need to enable dom.webcomponents.enabled and dom.webcomponents.customelements.enabled in older browsers |
| Edge| Currently it is in progress|
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53. ### What are custom elements?
Custom elements (or Web Components) are a Web Platform feature which extends HTML by allowing you to define a tag whose content is created and controlled by JavaScript code. The browser maintains a `CustomElementRegistry` of defined custom elements, which maps an instantiable JavaScript class to an HTML tag. Currently this feature is supported by Chrome, Firefox, Opera, and Safari, and available in other browsers through polyfills.
**[⬆ Back to Top](#table-of-contents)**
54. ### Do I need to bootstrap custom elements?
No, custom elements bootstrap (or start) automatically when they are added to the DOM, and are automatically destroyed when removed from the DOM. Once a custom element is added to the DOM for any page, it looks and behaves like any other HTML element, and does not require any special knowledge of Angular.
**[⬆ Back to Top](#table-of-contents)**
55. ### Explain how custom elements works internally?
Below are the steps in an order about custom elements functionality,
1. **App registers custom element with browser:** Use the `createCustomElement()` function to convert a component into a class that can be registered with the browser as a custom element.
2. **App adds custom element to DOM:** Add custom element just like a built-in HTML element directly into the DOM.
3. **Browser instantiate component based class:** Browser creates an instance of the registered class and adds it to the DOM.
4. **Instance provides content with data binding and change detection:** The content with in template is rendered using the component and DOM data.
The flow chart of the custom elements functionality would be as follows,
**[⬆ Back to Top](#table-of-contents)**
56. ### How to transfer components to custom elements?
Transforming components to custom elements involves **two** major steps,
1. **Build custom element class:** Angular provides the `createCustomElement()` function for converting an Angular component (along with its dependencies) to a custom element. The conversion process implements `NgElementConstructor` interface, and creates a constructor class which is used to produce a self-bootstrapping instance of Angular component.
2. **Register element class with browser:** It uses `customElements.define()` JS function, to register the configured constructor and its associated custom-element tag with the browser's `CustomElementRegistry`. When the browser encounters the tag for the registered element, it uses the constructor to create a custom-element instance.
The detailed structure would be as follows,
**[⬆ Back to Top](#table-of-contents)**
57. ### What are the mapping rules between Angular component and custom element?
The Component properties and logic maps directly into HTML attributes and the browser's event system. Let us describe them in two steps,
1. The createCustomElement() API parses the component input properties with corresponding attributes for the custom element. For example, component @Input('myInputProp') converted as custom element attribute `my-input-prop`.
2. The Component outputs are dispatched as HTML Custom Events, with the name of the custom event matching the output name. For example, component @Output() valueChanged = new EventEmitter() converted as custom element with dispatch event as "valueChanged".
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58. ### How do you define typings for custom elements?
You can use the `NgElement` and `WithProperties` types exported from @angular/elements.
Let's see how it can be applied by comparing with Angular component.
1. The simple container with input property would be as below,
```javascript
@Component(...)
class MyContainer {
@Input() message: string;
}
```
2. After applying types typescript validates input value and their types,
```javascirpt
const container = document.createElement('my-container') as NgElement & WithProperties<{message: string}>;
container.message = 'Welcome to Angular elements!';
container.message = true; // <-- ERROR: TypeScript knows this should be a string.
container.greet = 'News'; // <-- ERROR: TypeScript knows there is no `greet` property on `container`.
```
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59. ### What are dynamic components?
Dynamic components are the components in which the component's location in the application is not defined at build time i.e. they are not used in any angular template. Instead, the component is instantiated and placed in the application at runtime.
**[⬆ Back to Top](#table-of-contents)**
60. ### What are the various kinds of directives?
There are mainly three kinds of directives:
1. **Components** — These are directives with a template.
2. **Structural directives** — These directives change the DOM layout by adding and removing DOM elements.
3. **Attribute directives** — These directives change the appearance or behavior of an element, component, or another directive.
**[⬆ Back to Top](#table-of-contents)**
61. ### How do you create directives using CLI?
You can use CLI command `ng generate directive` to create the directive class file. It creates the source file(`src/app/components/directivename.directive.ts`), the respective test file `.spec.ts` and declare the directive class file in root module.
**[⬆ Back to Top](#table-of-contents)**
62. ### Give an example for attribute directives?
Let's take simple highlighter behavior as a example directive for DOM element. You can create and apply the attribute directive using below step:
1. Create HighlightDirective class with the file name `src/app/highlight.directive.ts`. In this file, we need to import **Directive** from core library to apply the metadata and **ElementRef** in the directive's constructor to inject a reference to the host DOM element ,
```javascript
import { Directive, ElementRef } from '@angular/core';
@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
constructor(el: ElementRef) {
el.nativeElement.style.backgroundColor = 'red';
}
}
```
2. Apply the attribute directive as an attribute to the host element(for example, <p>)
```javascript
<p appHighlight>Highlight me!</p>
```
3. Run the application to see the highlight behavior on paragraph element
```javascript
ng serve
```
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63. ### What is Angular Router?
Angular Router is a mechanism in which navigation happens from one view to the next as users perform application tasks. It borrows the concepts or model of browser's application navigation. It enables developers to build Single Page Applications with multiple views and allow navigation between these views.
**[⬆ Back to Top](#table-of-contents)**
64. ### What is the purpose of base href tag?
The routing application should add <base> element to the index.html as the first child in the <head> tag in order to indicate how to compose navigation URLs. If app folder is the application root then you can set the href value as below
```html
<base href="/">
```
**[⬆ Back to Top](#table-of-contents)**
65. ### What are the router imports?
The Angular Router which represents a particular component view for a given URL is not part of Angular Core. It is available in library named `@angular/router` to import required router components. For example, we import them in app module as below,
```javascript
import { RouterModule, Routes } from '@angular/router';
```
**[⬆ Back to Top](#table-of-contents)**
66. ### What is router outlet?
The RouterOutlet is a directive from the router library and it acts as a placeholder that marks the spot in the template where the router should display the components for that outlet. Router outlet is used like a component,
```html
<router-outlet></router-outlet>
<!-- Routed components go here -->
```
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67. ### What are router links?
The RouterLink is a directive on the anchor tags give the router control over those elements. Since the navigation paths are fixed, you can assign string values to router-link directive as below,
```html
<h1>Angular Router</h1>
<nav>
<a routerLink="/todosList" >List of todos</a>
<a routerLink="/completed" >Completed todos</a>
</nav>
<router-outlet></router-outlet>
```
**[⬆ Back to Top](#table-of-contents)**
68. ### What are active router links?
RouterLinkActive is a directive that toggles css classes for active RouterLink bindings based on the current RouterState. i.e, The Router will add CSS classes when this link is active and remove when the link is inactive. For example, you can add them to RouterLinks as below.
```html
<h1>Angular Router</h1>
<nav>
<a routerLink="/todosList" routerLinkActive="active">List of todos</a>
<a routerLink="/completed" routerLinkActive="active">Completed todos</a>
</nav>
<router-outlet></router-outlet>
```
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69. ### What is router state?
RouterState is a tree of activated routes. Every node in this tree knows about the "consumed" URL segments, the extracted parameters, and the resolved data. You can access the current RouterState from anywhere in the application using the `Router service` and the `routerState` property.
```javascript
@Component({templateUrl:'template.html'})
class MyComponent {
constructor(router: Router) {
const state: RouterState = router.routerState;
const root: ActivatedRoute = state.root;
const child = root.firstChild;
const id: Observable<string> = child.params.map(p => p.id);
//...
}
}
```
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70. ### What are router events?
During each navigation, the Router emits navigation events through the Router.events property allowing you to track the lifecycle of the route.
The sequence of router events is as below,
1. NavigationStart,
2. RouteConfigLoadStart,
3. RouteConfigLoadEnd,
4. RoutesRecognized,
5. GuardsCheckStart,
6. ChildActivationStart,
7. ActivationStart,
8. GuardsCheckEnd,
9. ResolveStart,
10. ResolveEnd,
11. ActivationEnd
12. ChildActivationEnd
13. NavigationEnd,
14. NavigationCancel,
15. NavigationError
16. Scroll
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71. ### What is activated route?
ActivatedRoute contains the information about a route associated with a component loaded in an outlet. It can also be used to traverse the router state tree. The ActivatedRoute will be injected as a router service to access the information. In the below example, you can access route path and parameters,
```javascript
@Component({...})
class MyComponent {
constructor(route: ActivatedRoute) {
const id: Observable<string> = route.params.pipe(map(p => p.id));
const url: Observable<string> = route.url.pipe(map(segments => segments.join('')));
// route.data includes both `data` and `resolve`
const user = route.data.pipe(map(d => d.user));
}
}
```
**[⬆ Back to Top](#table-of-contents)**
72. ### How do you define routes?
A router must be configured with a list of route definitions. You configures the router with routes via the `RouterModule.forRoot()` method, and adds the result to the AppModule's `imports` array.
```javascript
const appRoutes: Routes = [
{ path: 'todo/:id', component: TodoDetailComponent },
{
path: 'todos',
component: TodosListComponent,
data: { title: 'Todos List' }
},
{ path: '',
redirectTo: '/todos',
pathMatch: 'full'
},
{ path: '**', component: PageNotFoundComponent }
];
@NgModule({
imports: [
RouterModule.forRoot(
appRoutes,
{ enableTracing: true } // <-- debugging purposes only
)
// other imports here
],
...
})
export class AppModule { }
```
**[⬆ Back to Top](#table-of-contents)**
73. ### What is the purpose of Wildcard route?
If the URL doesn't match any predefined routes then it causes the router to throw an error and crash the app. In this case, you can use wildcard route. A wildcard route has a path consisting of two asterisks to match every URL.
For example, you can define PageNotFoundComponent for wildcard route as below
```javascript
{ path: '**', component: PageNotFoundComponent }
```
**[⬆ Back to Top](#table-of-contents)**
74. ### Do I need a Routing Module always?
No, the Routing Module is a design choice. You can skip routing Module (for example, AppRoutingModule) when the configuration is simple and merge the routing configuration directly into the companion module (for example, AppModule). But it is recommended when the configuration is complex and includes specialized guard and resolver services.
**[⬆ Back to Top](#table-of-contents)**
75. ### What is Angular Universal?
Angular Universal is a server-side rendering module for Angular applications in various scenarios. This is a community driven project and available under @angular/platform-server package. Recently Angular Universal is integrated with Angular CLI.
**[⬆ Back to Top](#table-of-contents)**
76. ### What are different types of compilation in Angular?
Angular offers two ways to compile your application,
1. Just-in-Time (JIT)
2. Ahead-of-Time (AOT)
**[⬆ Back to Top](#table-of-contents)**
77. ### What is JIT?
Just-in-Time (JIT) is a type of compilation that compiles your app in the browser at runtime. JIT compilation was the default until Angular 8, now default is AOT. When you run the ng build (build only) or ng serve (build and serve locally) CLI commands, the type of compilation (JIT or AOT) depends on the value of the aot property in your build configuration specified in angular.json. By default, aot is set to true.
**[⬆ Back to Top](#table-of-contents)**
78. ### What is AOT?
Ahead-of-Time (AOT) is a type of compilation that compiles your app at build time. This is the default starting in Angular 9. When you run the ng build (build only) or ng serve (build and serve locally) CLI commands, the type of compilation (JIT or AOT) depends on the value of the aot property in your build configuration specified in angular.json. By default, aot is set to true.
```cmd
ng build
ng serve
```
**[⬆ Back to Top](#table-of-contents)**
79. ### Why do we need compilation process?
The Angular components and templates cannot be understood by the browser directly. Due to that Angular applications require a compilation process before they can run in a browser. For example, In AOT compilation, both Angular HTML and TypeScript code converted into efficient JavaScript code during the build phase before browser runs it.
**[⬆ Back to Top](#table-of-contents)**
80. ### What are the advantages with AOT?
Below are the list of AOT benefits,
1. **Faster rendering:** The browser downloads a pre-compiled version of the application. So it can render the application immediately without compiling the app.
2. **Fewer asynchronous requests:** It inlines external HTML templates and CSS style sheets within the application javascript which eliminates separate ajax requests.
3. **Smaller Angular framework download size:** Doesn't require downloading the Angular compiler. Hence it dramatically reduces the application payload.
4. **Detect template errors earlier:** Detects and reports template binding errors during the build step itself
5. **Better security:** It compiles HTML templates and components into JavaScript. So there won't be any injection attacks.
**[⬆ Back to Top](#table-of-contents)**
81. ### What are the ways to control AOT compilation?
You can control your app compilation in two ways,
1. By providing template compiler options in the `tsconfig.json` file
2. By configuring Angular metadata with decorators
**[⬆ Back to Top](#table-of-contents)**
82. ### What are the restrictions of metadata?
In Angular, You must write metadata with the following general constraints,
1. Write expression syntax with in the supported range of javascript features
2. The compiler can only reference symbols which are exported
3. Only call the functions supported by the compiler
4. Decorated and data-bound class members must be public.
**[⬆ Back to Top](#table-of-contents)**
83. ### What are the three phases of AOT?
The AOT compiler works in three phases,
1. **Code Analysis:** The compiler records a representation of the source
2. **Code generation:** It handles the interpretation as well as places restrictions on what it interprets.
3. **Validation:** In this phase, the Angular template compiler uses the TypeScript compiler to validate the binding expressions in templates.
**[⬆ Back to Top](#table-of-contents)**
84. ### Can I use arrow functions in AOT?
No, Arrow functions or lambda functions can’t be used to assign values to the decorator properties. For example, the following snippet is invalid:
```javascript
@Component({
providers: [{
provide: MyService, useFactory: () => getService()
}]
})
```
To fix this, it has to be changed as following exported function:
```javascript
function getService(){
return new MyService();
}
@Component({
providers: [{
provide: MyService, useFactory: getService
}]
})
```
If you still use arrow function, it generates an error node in place of the function. When the compiler later interprets this node, it reports an error to turn the arrow function into an exported function.
**Note:** From Angular5 onwards, the compiler automatically performs this rewriting while emitting the .js file.
**[⬆ Back to Top](#table-of-contents)**
85. ### What is the purpose of metadata json files?
The metadata.json file can be treated as a diagram of the overall structure of a decorator's metadata, represented as an abstract syntax tree(AST). During the analysis phase, the AOT collector scan the metadata recorded in the Angular decorators and outputs metadata information in .metadata.json files, one per .d.ts file.
**[⬆ Back to Top](#table-of-contents)**
86. ### Can I use any javascript feature for expression syntax in AOT?
No, the AOT collector understands a subset of (or limited) JavaScript features. If an expression uses unsupported syntax, the collector writes an error node to the .metadata.json file. Later point of time, the compiler reports an error if it needs that piece of metadata to generate the application code.
**[⬆ Back to Top](#table-of-contents)**
87. ### What is folding?
The compiler can only resolve references to exported symbols in the metadata. Where as some of the non-exported members are folded while generating the code. i.e Folding is a process in which the collector evaluate an expression during collection and record the result in the .metadata.json instead of the original expression.
For example, the compiler couldn't refer selector reference because it is not exported
```javascript
let selector = 'app-root';
@Component({
selector: selector
})
```
Will be folded into inline selector
```javascript
@Component({
selector: 'app-root'
})
```
Remember that the compiler can’t fold everything. For example, spread operator on arrays, objects created using new keywords and function calls.
**[⬆ Back to Top](#table-of-contents)**
88. ### What are macros?
The AOT compiler supports macros in the form of functions or static methods that return an expression in a `single return expression`.
For example, let us take a below macro function,
```javascript
export function wrapInArray<T>(value: T): T[] {
return [value];
}
```
You can use it inside metadata as an expression,
```javascript
@NgModule({
declarations: wrapInArray(TypicalComponent)
})
export class TypicalModule {}
```
The compiler treats the macro expression as it written directly
```javascript
@NgModule({
declarations: [TypicalComponent]
})
export class TypicalModule {}
```
**[⬆ Back to Top](#table-of-contents)**
89. ### Give an example of few metadata errors?
Below are some of the errors encountered in metadata,
1. **Expression form not supported:** Some of the language features outside of the compiler's restricted expression syntax used in angular metadata can produce this error.
Let's see some of these examples,
```javascript
1. export class User { ... }
const prop = typeof User; // typeof is not valid in metadata
2. { provide: 'token', useValue: { [prop]: 'value' } }; // bracket notation is not valid in metadata
```
2. **Reference to a local (non-exported) symbol:** The compiler encountered a referenced to a locally defined symbol that either wasn't exported or wasn't initialized.
Let's take example of this error,
```javascript
// ERROR
let username: string; // neither exported nor initialized
@Component({
selector: 'my-component',
template: ... ,
providers: [
{ provide: User, useValue: username }
]
})
export class MyComponent {}
```
You can fix this by either exporting or initializing the value,
```javascript
export let username: string; // exported
(or)
let username = 'John'; // initialized
```
3. **Function calls are not supported:** The compiler does not currently support function expressions or lambda functions. For example, you cannot set a provider's useFactory to an anonymous function or arrow function as below.
```javascript
providers: [
{ provide: MyStrategy, useFactory: function() { ... } },
{ provide: OtherStrategy, useFactory: () => { ... } }
]
```
You can fix this with exported function
```javascript
export function myStrategy() { ... }
export function otherStrategy() { ... }
... // metadata
providers: [
{ provide: MyStrategy, useFactory: myStrategy },
{ provide: OtherStrategy, useFactory: otherStrategy },
```
4. **Destructured variable or constant not supported:** The compiler does not support references to variables assigned by destructuring.
For example, you cannot write something like this:
```javascript
import { user } from './user';
// destructured assignment to name and age
const {name, age} = user;
... //metadata
providers: [
{provide: Name, useValue: name},
{provide: Age, useValue: age},
]
```
You can fix this by non-destructured values
```javscript
import { user } from './user';
... //metadata
providers: [
{provide: Name, useValue: user.name},
{provide: Age, useValue: user.age},
]
```
**[⬆ Back to Top](#table-of-contents)**
90. ### What is metadata rewriting?
Metadata rewriting is the process in which the compiler converts the expression initializing the fields such as useClass, useValue, useFactory, and data into an exported variable, which replaces the expression. Remember that the compiler does this rewriting during the emit of the .js file but not in definition files( .d.ts file).
**[⬆ Back to Top](#table-of-contents)**
91. ### How do you provide configuration inheritance?
Angular Compiler supports configuration inheritance through extends in the tsconfig.json on angularCompilerOptions. i.e, The configuration from the base file(for example, tsconfig.base.json) are loaded first, then overridden by those in the inheriting config file.
```javascript
{
"extends": "../tsconfig.base.json",
"compilerOptions": {
"experimentalDecorators": true,
...
},
"angularCompilerOptions": {
"fullTemplateTypeCheck": true,
"preserveWhitespaces": true,
...
}
}
```
**[⬆ Back to Top](#table-of-contents)**
92. ### How do you specify angular template compiler options?
The angular template compiler options are specified as members of the **angularCompilerOptions** object in the tsconfig.json file. These options will be specified adjecent to typescript compiler options.
```javascript
{
"compilerOptions": {
"experimentalDecorators": true,
...
},
"angularCompilerOptions": {
"fullTemplateTypeCheck": true,
"preserveWhitespaces": true,
...
}
}
```
**[⬆ Back to Top](#table-of-contents)**
93. ### How do you enable binding expression validation?
You can enable binding expression validation explicitly by adding the compiler option **fullTemplateTypeCheck** in the "angularCompilerOptions" of the project's tsconfig.json. It produces error messages when a type error is detected in a template binding expression.
For example, consider the following component:
```javascript
@Component({
selector: 'my-component',
template: '{{user.contacts.email}}'
})
class MyComponent {
user?: User;
}
```
This will produce the following error:
```javascript
my.component.ts.MyComponent.html(1,1): : Property 'contacts' does not exist on type 'User'. Did you mean 'contact'?
```
**[⬆ Back to Top](#table-of-contents)**
94. ### What is the purpose of any type cast function?
You can disable binding expression type checking using $any() type cast function(by surrounding the expression). In the following example, the error Property contacts does not exist is suppressed by casting user to the any type.
```javascript
template:
'{{ $any(user).contacts.email }}'
```
The $any() cast function also works with this to allow access to undeclared members of the component.
```javascript
template:
'{{ $any(this).contacts.email }}'
```
**[⬆ Back to Top](#table-of-contents)**
95. ### What is Non null type assertion operator?
You can use the non-null type assertion operator to suppress the Object is possibly 'undefined' error. In the following example, the user and contact properties are always set together, implying that contact is always non-null if user is non-null. The error is suppressed in the example by using contact!.email.
```javascript
@Component({
selector: 'my-component',
template: '<span *ngIf="user"> {{user.name}} contacted through {{contact!.email}} </span>'
})
class MyComponent {
user?: User;
contact?: Contact;
setData(user: User, contact: Contact) {
this.user = user;
this.contact = contact;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
96. ### What is type narrowing?
The expression used in an ngIf directive is used to narrow type unions in the Angular template compiler similar to if expression in typescript. So *ngIf allows the typeScript compiler to infer that the data used in the binding expression will never be undefined.
```javascript
@Component({
selector: 'my-component',
template: '<span *ngIf="user"> {{user.contact.email}} </span>'
})
class MyComponent {
user?: User;
}
```
**[⬆ Back to Top](#table-of-contents)**
97. ### How do you describe various dependencies in angular application?
The dependencies section of package.json with in an angular application can be divided as follow,
1. **Angular packages:** Angular core and optional modules; their package names begin @angular/.
2. **Support packages:** Third-party libraries that must be present for Angular apps to run.
3. **Polyfill packages:** Polyfills plug gaps in a browser's JavaScript implementation.
**[⬆ Back to Top](#table-of-contents)**
98. ### What is zone?
A Zone is an execution context that persists across async tasks. Angular relies on zone.js to run Angular's change detection processes when native JavaScript operations raise events
**[⬆ Back to Top](#table-of-contents)**
99. ### What is the purpose of common module?
The commonly-needed services, pipes, and directives provided by @angular/common module. Apart from these HttpClientModule is available under @angular/common/http.
**[⬆ Back to Top](#table-of-contents)**
100. ### What is codelyzer?
Codelyzer provides set of tslint rules for static code analysis of Angular TypeScript projects. You can run the static code analyzer over web apps, NativeScript, Ionic etc. Angular CLI has support for this and it can be use as below,
```bash
ng new codelyzer
ng lint
```
**[⬆ Back to Top](#table-of-contents)**
101. ### What is angular animation?
Angular's animation system is built on CSS functionality in order to animate any property that the browser considers animatable. These properties includes positions, sizes, transforms, colors, borders etc. The Angular modules for animations are **@angular/animations** and **@angular/platform-browser** and these dependencies are automatically added to your project when you create a project using Angular CLI.
**[⬆ Back to Top](#table-of-contents)**
102. ### What are the steps to use animation module?
You need to follow below steps to implement animation in your angular project,
1. **Enabling the animations module:** Import BrowserAnimationsModule to add animation capabilities into your Angular root application module(for example, src/app/app.module.ts).
```javascript
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
@NgModule({
imports: [
BrowserModule,
BrowserAnimationsModule
],
declarations: [ ],
bootstrap: [ ]
})
export class AppModule { }
```
2. **Importing animation functions into component files:** Import required animation functions from @angular/animations in component files(for example, src/app/app.component.ts).
```javascript
import {
trigger,
state,
style,
animate,
transition,
// ...
} from '@angular/animations';
```
3. **Adding the animation metadata property:** add a metadata property called animations: within the @Component() decorator in component files(for example, src/app/app.component.ts)
```javascript
@Component({
selector: 'app-root',
templateUrl: 'app.component.html',
styleUrls: ['app.component.css'],
animations: [
// animation triggers go here
]
})
```
**[⬆ Back to Top](#table-of-contents)**
103. ### What is State function?
Angular's state() function is used to define different states to call at the end of each transition. This function takes two arguments: a unique name like open or closed and a style() function.
For example, you can write a open state function
```javascript
state('open', style({
height: '300px',
opacity: 0.5,
backgroundColor: 'blue'
})),
```
**[⬆ Back to Top](#table-of-contents)**
104. ### What is Style function?
The style function is used to define a set of styles to associate with a given state name. You need to use it along with state() function to set CSS style attributes. For example, in the close state, the button has a height of 100 pixels, an opacity of 0.8, and a background color of green.
```javascript
state('close', style({
height: '100px',
opacity: 0.8,
backgroundColor: 'green'
})),
```
**Note:** The style attributes must be in camelCase.
**[⬆ Back to Top](#table-of-contents)**
105. ### What is the purpose of animate function?
Angular Animations are a powerful way to implement sophisticated and compelling animations for your Angular single page web application.
```javascript
import { Component, OnInit, Input } from '@angular/core';
import { trigger, state, style, animate, transition } from '@angular/animations';
@Component({
selector: 'app-animate',
templateUrl: `<div [@changeState]="currentState" class="myblock mx-auto"></div>`,
styleUrls: `.myblock {
background-color: green;
width: 300px;
height: 250px;
border-radius: 5px;
margin: 5rem;
}`,
animations: [
trigger('changeState', [
state('state1', style({
backgroundColor: 'green',
transform: 'scale(1)'
})),
state('state2', style({
backgroundColor: 'red',
transform: 'scale(1.5)'
})),
transition('*=>state1', animate('300ms')),
transition('*=>state2', animate('2000ms'))
])
]
})
export class AnimateComponent implements OnInit {
@Input() currentState;
constructor() { }
ngOnInit() {
}
}
```
**[⬆ Back to Top](#table-of-contents)**
106. ### What is transition function?
The animation transition function is used to specify the changes that occur between one state and another over a period of time. It accepts two arguments: the first argument accepts an expression that defines the direction between two transition states, and the second argument accepts an animate() function.
Let's take an example state transition from open to closed with an half second transition between states.
```javascript
transition('open => closed', [
animate('500ms')
]),
```
**[⬆ Back to Top](#table-of-contents)**
107. ### How to inject the dynamic script in angular?
Using DomSanitizer we can inject the dynamic Html,Style,Script,Url.
```
import { Component, OnInit } from '@angular/core';
import { DomSanitizer } from '@angular/platform-browser';
@Component({
selector: 'my-app',
template: `
<div [innerHtml]="htmlSnippet"></div>
`,
})
export class App {
constructor(protected sanitizer: DomSanitizer) {}
htmlSnippet: string = this.sanitizer.bypassSecurityTrustScript("<script>safeCode()</script>");
}
```
**[⬆ Back to Top](#table-of-contents)**
108. ### What is a service worker and its role in Angular?
A service worker is a script that runs in the web browser and manages caching for an application. Starting from 5.0.0 version, Angular ships with a service worker implementation. Angular service worker is designed to optimize the end user experience of using an application over a slow or unreliable network connection, while also minimizing the risks of serving outdated content.
**[⬆ Back to Top](#table-of-contents)**
109. ### What are the design goals of service workers?
Below are the list of design goals of Angular's service workers,
1. It caches an application just like installing a native application
2. A running application continues to run with the same version of all files without any incompatible files
3. When you refresh the application, it loads the latest fully cached version
4. When changes are published then it immediately updates in the background
5. Service workers saves the bandwidth by downloading the resources only when they changed.
**[⬆ Back to Top](#table-of-contents)**
110. ### What are the differences between AngularJS and Angular with respect to dependency injection?
Dependency injection is a common component in both AngularJS and Angular, but there are some key differences between the two frameworks in how it actually works.
| AngularJS | Angular |
|---- | ---------
| Dependency injection tokens are always strings | Tokens can have different types. They are often classes and sometimes can be strings. |
| There is exactly one injector even though it is a multi-module applications | There is a tree hierarchy of injectors, with a root injector and an additional injector for each component. |
**[⬆ Back to Top](#table-of-contents)**
111. ### What is Angular Ivy?
Angular Ivy is a new rendering engine for Angular. You can choose to opt in a preview version of Ivy from Angular version 8.
1. You can enable ivy in a new project by using the --enable-ivy flag with the ng new command
```bash
ng new ivy-demo-app --enable-ivy
```
2. You can add it to an existing project by adding `enableIvy` option in the `angularCompilerOptions` in your project's `tsconfig.app.json`.
```javascript
{
"compilerOptions": { ... },
"angularCompilerOptions": {
"enableIvy": true
}
}
```
**[⬆ Back to Top](#table-of-contents)**
112. ### What are the features included in ivy preview?
You can expect below features with Ivy preview,
1. Generated code that is easier to read and debug at runtime
2. Faster re-build time
3. Improved payload size
4. Improved template type checking
**[⬆ Back to Top](#table-of-contents)**
113. ### Can I use AOT compilation with Ivy?
Yes, it is a recommended configuration. Also, AOT compilation with Ivy is faster. So you need set the default build options(with in angular.json) for your project to always use AOT compilation.
```javascript
{
"projects": {
"my-project": {
"architect": {
"build": {
"options": {
...
"aot": true,
}
}
}
}
}
}
```
**[⬆ Back to Top](#table-of-contents)**
114. ### What is Angular Language Service?
The Angular Language Service is a way to get completions, errors, hints, and navigation inside your Angular templates whether they are external in an HTML file or embedded in annotations/decorators in a string. It has the ability to autodetect that you are opening an Angular file, reads your `tsconfig.json` file, finds all the templates you have in your application, and then provides all the language services.
**[⬆ Back to Top](#table-of-contents)**
115. ### How do you install angular language service in the project?
You can install Angular Language Service in your project with the following npm command,
```javascript
npm install --save-dev @angular/language-service
```
After that add the following to the "compilerOptions" section of your project's tsconfig.json
```javascript
"plugins": [
{"name": "@angular/language-service"}
]
```
**Note:** The completion and diagnostic services works for .ts files only. You need to use custom plugins for supporting HTML files.
**[⬆ Back to Top](#table-of-contents)**
116. ### Is there any editor support for Angular Language Service?
Yes, Angular Language Service is currently available for Visual Studio Code and WebStorm IDEs. You need to install angular language service using an extension and devDependency respectively. In sublime editor, you need to install typescript which has has a language service plugin model.
**[⬆ Back to Top](#table-of-contents)**
117. ### Explain the features provided by Angular Language Service?
Basically there are 3 main features provided by Angular Language Service,
1. **Autocompletion:** Autocompletion can speed up your development time by providing you with contextual possibilities and hints as you type with in an interpolation and elements.
2. **Error checking:** It can also warn you of mistakes in your code.
3. **Navigation:** Navigation allows you to hover a component, directive, module and then click and press F12 to go directly to its definition.
**[⬆ Back to Top](#table-of-contents)**
118. ### How do you add web workers in your application?
You can add web worker anywhere in your application. For example, If the file that contains your expensive computation is `src/app/app.component.ts`, you can add a Web Worker using `ng generate web-worker app` command which will create `src/app/app.worker.ts` web worker file. This command will perform below actions,
1. Configure your project to use Web Workers
2. Adds app.worker.ts to receive messages
```javascript
addEventListener('message', ({ data }) => {
const response = `worker response to ${data}`;
postMessage(response);
});
```
3. The component `app.component.ts` file updated with web worker file
```javascript
if (typeof Worker !== 'undefined') {
// Create a new
const worker = new Worker('./app.worker', { type: 'module' });
worker.onmessage = ({ data }) => {
console.log('page got message: $\{data\}');
};
worker.postMessage('hello');
} else {
// Web Workers are not supported in this environment.
}
```
**Note:** You may need to refactor your initial scaffolding web worker code for sending messages to and from.
**[⬆ Back to Top](#table-of-contents)**
119. ### What are the limitations with web workers?
You need to remember two important things when using Web Workers in Angular projects,
1. Some environments or platforms(like @angular/platform-server) used in Server-side Rendering, don't support Web Workers. In this case you need to provide a fallback mechanism to perform the computations to work in this environments.
2. Running Angular in web worker using `@angular/platform-webworker` is not yet supported in Angular CLI.
**[⬆ Back to Top](#table-of-contents)**
120. ### What is Angular CLI Builder?
In Angular8, the CLI Builder API is stable and available to developers who want to customize the `Angular CLI` by adding or modifying commands. For example, you could supply a builder to perform an entirely new task, or to change which third-party tool is used by an existing command.
**[⬆ Back to Top](#table-of-contents)**
121. ### What is a builder?
A builder function is a function that uses the `Architect API` to perform a complex process such as "build" or "test". The builder code is defined in an npm package. For example, BrowserBuilder runs a webpack build for a browser target and KarmaBuilder starts the Karma server and runs a webpack build for unit tests.
**[⬆ Back to Top](#table-of-contents)**
122. ### How do you invoke a builder?
The Angular CLI command `ng run` is used to invoke a builder with a specific target configuration. The workspace configuration file, `angular.json`, contains default configurations for built-in builders.
**[⬆ Back to Top](#table-of-contents)**
123. ### How do you create app shell in Angular?
An App shell is a way to render a portion of your application via a route at build time. This is useful to first paint of your application that appears quickly because the browser can render static HTML and CSS without the need to initialize JavaScript. You can achieve this using Angular CLI which generates an app shell for running server-side of your app.
```javascript
ng generate appShell [options] (or)
ng g appShell [options]
```
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124. ### What are the case types in Angular?
Angular uses capitalization conventions to distinguish the names of various types. Angular follows the list of the below case types.
1. **camelCase :** Symbols, properties, methods, pipe names, non-component directive selectors, constants uses lowercase on the first letter of the item. For example, "selectedUser"
2. **UpperCamelCase (or PascalCase):** Class names, including classes that define components, interfaces, NgModules, directives, and pipes uses uppercase on the first letter of the item.
3. **dash-case (or "kebab-case"):** The descriptive part of file names, component selectors uses dashes between the words. For example, "app-user-list".
4. **UPPER_UNDERSCORE_CASE:** All constants uses capital letters connected with underscores. For example, "NUMBER_OF_USERS".
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125. ### What are the class decorators in Angular?
A class decorator is a decorator that appears immediately before a class definition, which declares the class to be of the given type, and provides metadata suitable to the type
The following list of decorators comes under class decorators,
1. @Component()
2. @Directive()
3. @Pipe()
4. @Injectable()
5. @NgModule()
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126. ### What are class field decorators?
The class field decorators are the statements declared immediately before a field in a class definition that defines the type of that field. Some of the examples are: @input and @output,
```javascript
@Input() myProperty;
@Output() myEvent = new EventEmitter();
```
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127. ### What is declarable in Angular?
Declarable is a class type that you can add to the declarations list of an NgModule. The class types such as components, directives, and pipes comes can be declared in the module. The structure of declarations would be,
```javascript
declarations: [
YourComponent,
YourPipe,
YourDirective
],
```
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128. ### What are the restrictions on declarable classes?
Below classes shouldn't be declared,
1. A class that's already declared in another NgModule
2. Ngmodule classes
3. Service classes
4. Helper classes
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129. ### What is a DI token?
A DI token is a lookup token associated with a dependency provider in dependency injection system. The injector maintains an internal token-provider map that it references when asked for a dependency and the DI token is the key to the map. Let's take example of DI Token usage,
```javascript
const BASE_URL = new InjectionToken<string>('BaseUrl');
const injector =
Injector.create({providers: [{provide: BASE_URL, useValue: 'http://some-domain.com'}]});
const url = injector.get(BASE_URL);
```
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130. ### What is Angular DSL?
A domain-specific language (DSL) is a computer language specialized to a particular application domain. Angular has its own Domain Specific Language (DSL) which allows us to write Angular specific html-like syntax on top of normal html. It has its own compiler that compiles this syntax to html that the browser can understand. This DSL is defined in NgModules such as animations, forms, and routing and navigation.
Basically you will see 3 main syntax in Angular DSL.
1. `()`: Used for Output and DOM events.
2. `[]`: Used for Input and specific DOM element attributes.
3. `*`: Structural directives(*ngFor or *ngIf) will affect/change the DOM structure.
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131. ### what is an rxjs subject in Angular
An RxJS Subject is a special type of Observable that allows values to be multicasted to many Observers. While plain Observables are unicast (each subscribed Observer owns an independent execution of the Observable), Subjects are multicast.
A Subject is like an Observable, but can multicast to many Observers. Subjects are like EventEmitters: they maintain a registry of many listeners.
``` typescript
import { Subject } from 'rxjs';
const subject = new Subject<number>();
subject.subscribe({
next: (v) => console.log(`observerA: ${v}`)
});
subject.subscribe({
next: (v) => console.log(`observerB: ${v}`)
});
subject.next(1);
subject.next(2);
```
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132. ### What is Bazel tool?
Bazel is a powerful build tool developed and massively used by Google and it can keep track of the dependencies between different packages and build targets. In Angular8, you can build your CLI application with Bazel.
**Note:** The Angular framework itself is built with Bazel.
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133. ### What are the advantages of Bazel tool?
Below are the list of key advantages of Bazel tool,
1. It creates the possibility of building your back-ends and front-ends with the same tool
2. The incremental build and tests
3. It creates the possibility to have remote builds and cache on a build farm.
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134. ### How do you use Bazel with Angular CLI?
The @angular/bazel package provides a builder that allows Angular CLI to use Bazel as the build tool.
1. **Use in an existing applciation:** Add @angular/bazel using CLI
```javascript
ng add @angular/bazel
```
2. **Use in a new application:** Install the package and create the application with collection option
```javascript
npm install -g @angular/bazel
ng new --collection=@angular/bazel
```
When you use ng build and ng serve commands, Bazel is used behind the scenes and outputs the results in dist/bin folder.
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135. ### How do you run Bazel directly?
Sometimes you may want to bypass the Angular CLI builder and run Bazel directly using Bazel CLI. You can install it globally using @bazel/bazel npm package. i.e, Bazel CLI is available under @bazel/bazel package. After you can apply the below common commands,
```javascrippt
bazel build [targets] // Compile the default output artifacts of the given targets.
bazel test [targets] // Run the tests with *_test targets found in the pattern.
bazel run [target]: Compile the program represented by target and then run it.
```
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136. ### What is platform in Angular?
A platform is the context in which an Angular application runs. The most common platform for Angular applications is a web browser, but it can also be an operating system for a mobile device, or a web server. The runtime-platform is provided by the @angular/platform-* packages and these packages allow applications that make use of `@angular/core` and `@angular/common` to execute in different environments.
i.e, Angular can be used as platform-independent framework in different environments, For example,
1. While running in the browser, it uses `platform-browser` package.
2. When SSR(server-side rendering ) is used, it uses `platform-server` package for providing web server implementation.
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137. ### What happens if I import the same module twice?
If multiple modules imports the same module then angular evaluates it only once (When it encounters the module first time). It follows this condition even the module appears at any level in a hierarchy of imported NgModules.
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138. ### How do you select an element with in a component template?
You can use `@ViewChild` directive to access elements in the view directly. Let's take input element with a reference,
```html
<input #uname>
```
and define view child directive and access it in ngAfterViewInit lifecycle hook
```javascript
@ViewChild('uname') input;
ngAfterViewInit() {
console.log(this.input.nativeElement.value);
}
```
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139. ### How do you detect route change in Angular?
In Angular7, you can subscribe to router to detect the changes. The subscription for router events would be as below,
```javascript
this.router.events.subscribe((event: Event) => {})
```
Let's take a simple component to detect router changes
```javascript
import { Component } from '@angular/core';
import { Router, Event, NavigationStart, NavigationEnd, NavigationError } from '@angular/router';
@Component({
selector: 'app-root',
template: `<router-outlet></router-outlet>`
})
export class AppComponent {
constructor(private router: Router) {
this.router.events.subscribe((event: Event) => {
if (event instanceof NavigationStart) {
// Show loading indicator and perform an action
}
if (event instanceof NavigationEnd) {
// Hide loading indicator and perform an action
}
if (event instanceof NavigationError) {
// Hide loading indicator and perform an action
console.log(event.error); // It logs an error for debugging
}
});
}
}
```
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140. ### How do you pass headers for HTTP client?
You can directly pass object map for http client or create HttpHeaders class to supply the headers.
```javascript
constructor(private _http: HttpClient) {}
this._http.get('someUrl',{
headers: {'header1':'value1','header2':'value2'}
});
(or)
let headers = new HttpHeaders().set('header1', headerValue1); // create header object
headers = headers.append('header2', headerValue2); // add a new header, creating a new object
headers = headers.append('header3', headerValue3); // add another header
let params = new HttpParams().set('param1', value1); // create params object
params = params.append('param2', value2); // add a new param, creating a new object
params = params.append('param3', value3); // add another param
return this._http.get<any[]>('someUrl', { headers: headers, params: params })
```
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141. ### What is the purpose of differential loading in CLI?
From Angular8 release onwards, the applications are built using differential loading strategy from CLI to build two separate bundles as part of your deployed application.
1. The first build contains ES2015 syntax which takes the advantage of built-in support in modern browsers, ships less polyfills, and results in a smaller bundle size.
2. The second build contains old ES5 syntax to support older browsers with all necessary polyfills. But this results in a larger bundle size.
**Note:** This strategy is used to support multiple browsers but it only load the code that the browser needs.
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142. ### Is Angular supports dynamic imports?
Yes, Angular 8 supports dynamic imports in router configuration. i.e, You can use the import statement for lazy loading the module using `loadChildren` method and it will be understood by the IDEs(VSCode and WebStorm), webpack, etc.
Previously, you have been written as below to lazily load the feature module. By mistake, if you have typo in the module name it still accepts the string and throws an error during build time.
```javascript
{path: ‘user’, loadChildren: ‘./users/user.module#UserModulee’},
```
This problem is resolved by using dynamic imports and IDEs are able to find it during compile time itself.
```javascript
{path: ‘user’, loadChildren: () => import(‘./users/user.module’).then(m => m.UserModule)};
```
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143. ### What is lazy loading?
Lazy loading is one of the most useful concepts of Angular Routing. It helps us to download the web pages in chunks instead of downloading everything in a big bundle. It is used for lazy loading by asynchronously loading the feature module for routing whenever required using the property `loadChildren`. Let's load both `Customer` and `Order` feature modules lazily as below,
```javascript
const routes: Routes = [
{
path: 'customers',
loadChildren: () => import('./customers/customers.module').then(module => module.CustomersModule)
},
{
path: 'orders',
loadChildren: () => import('./orders/orders.module').then(module => module.OrdersModule)
},
{
path: '',
redirectTo: '',
pathMatch: 'full'
}
];
```
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144. ### What are workspace APIs?
Angular 8.0 release introduces Workspace APIs to make it easier for developers to read and modify the angular.json file instead of manually modifying it. Currently, the only supported storage3 format is the JSON-based format used by the Angular CLI. You can enable or add optimization option for build target as below,
```javascript
import { NodeJsSyncHost } from '@angular-devkit/core/node';
import { workspaces } from '@angular-devkit/core';
async function addBuildTargetOption() {
const host = workspaces.createWorkspaceHost(new NodeJsSyncHost());
const workspace = await workspaces.readWorkspace('path/to/workspace/directory/', host);
const project = workspace.projects.get('my-app');
if (!project) {
throw new Error('my-app does not exist');
}
const buildTarget = project.targets.get('build');
if (!buildTarget) {
throw new Error('build target does not exist');
}
buildTarget.options.optimization = true;
await workspaces.writeWorkspace(workspace, host);
}
addBuildTargetOption();
```
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145. ### How do you upgrade angular version?
The Angular upgrade is quite easier using Angular CLI `ng update` command as mentioned below. For example, if you upgrade from Angular 7 to 8 then your lazy loaded route imports will be migrated to the new import syntax automatically.
```bash
$ ng update @angular/cli @angular/core
```
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146. ### What is Angular Material?
Angular Material is a collection of Material Design components for Angular framework following the Material Design spec. You can apply Material Design very easily using Angular Material. The installation can be done through npm or yarn,
```bash
npm install --save @angular/material @angular/cdk @angular/animations
(OR)
yarn add @angular/material @angular/cdk @angular/animations
```
It supports the most recent two versions of all major browsers. The latest version of Angular material is 8.1.1
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147. ### How do you upgrade location service of angularjs?
If you are using `$location` service in your old AngularJS application, now you can use `LocationUpgradeModule`(unified location service) which puts the responsibilities of `$location` service to `Location` service in Angular. Let's add this module to `AppModule` as below,
```javascript
// Other imports ...
import { LocationUpgradeModule } from '@angular/common/upgrade';
@NgModule({
imports: [
// Other NgModule imports...
LocationUpgradeModule.config()
]
})
export class AppModule {}
```
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148. ### What is NgUpgrade?
NgUpgrade is a library put together by the Angular team, which you can use in your applications to mix and match AngularJS and Angular components and bridge the AngularJS and Angular dependency injection systems.
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149. ### How do you test Angular application using CLI?
Angular CLI downloads and install everything needed with the Jasmine Test framework. You just need to run `ng test` to see the test results. By default this command builds the app in watch mode, and launches the `Karma test runner`. The output of test results would be as below,
```bash
10% building modules 1/1 modules 0 active
...INFO [karma]: Karma v1.7.1 server started at http://0.0.0.0:9876/
...INFO [launcher]: Launching browser Chrome ...
...INFO [launcher]: Starting browser Chrome
...INFO [Chrome ...]: Connected on socket ...
Chrome ...: Executed 3 of 3 SUCCESS (0.135 secs / 0.205 secs)
```
**Note:** A chrome browser also opens and displays the test output in the "Jasmine HTML Reporter".
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150. ### How to use polyfills in Angular application?
The Angular CLI provides support for polyfills officially. When you create a new project with the ng new command, a `src/polyfills.ts` configuration file is created as part of your project folder. This file includes the mandatory and many of the optional polyfills as JavaScript import statements. Let's categorize the polyfills,
1. **Mandatory polyfills:** These are installed automatically when you create your project with ng new command and the respective import statements enabled in 'src/polyfills.ts' file.
2. **Optional polyfills:** You need to install its npm package and then create import statement in 'src/polyfills.ts' file.
For example, first you need to install below npm package for adding web animations (optional) polyfill.
```bash
npm install --save web-animations-js
```
and create import statement in polyfill file.
```javascript
import 'web-animations-js';
```
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151. ### What are the ways to trigger change detection in Angular?
You can inject either ApplicationRef or NgZone, or ChangeDetectorRef into your component and apply below specific methods to trigger change detection in Angular. i.e, There are 3 possible ways,
1. **ApplicationRef.tick():** Invoke this method to explicitly process change detection and its side-effects. It check the full component tree.
2. **NgZone.run(callback):** It evaluate the callback function inside the Angular zone.
3. **ChangeDetectorRef.detectChanges():** It detects only the components and it's children.
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152. ### What are the differences of various versions of Angular?
There are different versions of Angular framework. Let's see the features of all the various versions,
1. **Angular 1:**
* Angular 1 (AngularJS) is the first angular framework released in the year 2010.
* AngularJS is not built for mobile devices.
* It is based on controllers with MVC architecture.
2. **Angular 2:**
* Angular 2 was released in the year 2016. Angular 2 is a complete rewrite of Angular1 version.
* The performance issues that Angular 1 version had has been addressed in Angular 2 version.
* Angular 2 is built from scratch for mobile devices unlike Angular 1 version.
* Angular 2 is components based.
3. **Angular 3:**
* The following are the different package versions in Angular 2:
* @angular/core v2.3.0
* @angular/compiler v2.3.0
* @angular/http v2.3.0
* @angular/router v3.3.0
* The router package is already versioned 3 so to avoid confusion switched to Angular 4 version and skipped 3 version.
4. **Angular 4:**
* The compiler generated code file size in AOT mode is very much reduced.
* With Angular 4 the production bundles size is reduced by hundreds of KB’s.
* Animation features are removed from angular/core and formed as a separate package.
* Supports Typescript 2.1 and 2.2.
* Angular Universal
* New HttpClient
5. **Angular 5:**
* Angular 5 makes angular faster. It improved the loading time and execution time.
* Shipped with new build optimizer.
* Supports Typescript 2.5.
* Service Worker
6. **Angular 6:**
* It is released in May 2018.
* Includes Angular Command Line Interface (CLI), Component Development KIT (CDK), Angular Material Package, Angular Elements.
* Service Worker bug fixes.
* i18n
* Experimental mode for Ivy.
* RxJS 6.0
* Tree Shaking
7. **Angular 7:**
* It is released in October 2018.
* TypeScript 3.1
* RxJS 6.3
* New Angular CLI
* CLI Prompts capability provide an ability to ask questions to the user before they run. It is like interactive dialog between the user and the CLI
* With the improved CLI Prompts capability, it helps developers to make the decision. New ng commands ask users for routing and CSS styles types(SCSS) and ng add @angular/material asks for themes and gestures or animations.
8. **Angular 8:**
* It is released in May 2019.
* TypeScript 3.4
9. **Angular 9:**
* It is released in February 2020.
* TypeScript 3.7
* Ivy enabled by default
10. **Angular 10:**
* It is released in June 2020.
* TypeScript 3.9
* TSlib 2.0
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153. ### What are the security principles in angular?
Below are the list of security principles in angular,
1. You should avoid direct use of the DOM APIs.
2. You should enable Content Security Policy (CSP) and configure your web server to return appropriate CSP HTTP headers.
3. You should Use the offline template compiler.
4. You should Use Server Side XSS protection.
5. You should Use DOM Sanitizer.
6. You should Preventing CSRF or XSRF attacks.
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154. ### What is the reason to deprecate Web Tracing Framework?
Angular has supported the integration with the Web Tracing Framework (WTF) for the purpose of performance testing. Since it is not well maintained and failed in majority of the applications, the support is deprecated in latest releases.
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155. ### What is the reason to deprecate web worker packages?
Both `@angular/platform-webworker` and `@angular/platform-webworker-dynamic` are officially deprecated, the Angular team realized it's not good practice to run the Angular application on Web worker
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156. ### How do you find angular CLI version?
Angular CLI provides it's installed version using below different ways using ng command,
```bash
ng v
ng version
ng -v
ng --version
```
and the output would be as below,
```bash
Angular CLI: 1.6.3
Node: 8.11.3
OS: darwin x64
Angular:
...
```
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157. ### What is the browser support for Angular?
Angular supports most recent browsers which includes both desktop and mobile browsers.
| Browser | Version |
|---- | --------- |
| Chrome | latest |
| Firefox | latest |
| Edge | 2 most recent major versions |
| IE | 11, 10, 9 (Compatibility mode is not supported) |
| Safari | 2 most recent major versions |
| IE Mobile | 11 |
| iOS | 2 most recent major versions |
| Android | 7.0, 6.0, 5.0, 5.1, 4.4 |
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158. ### What is schematic?
It's a scaffolding library that defines how to generate or transform a programming project by creating, modifying, refactoring, or moving files and code. It defines rules that operate on a virtual file system called a tree.
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159. ### What is rule in Schematics?
In schematics world, it's a function that operates on a file tree to create, delete, or modify files in a specific manner.
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160. ### What is Schematics CLI?
Schematics come with their own command-line tool known as Schematics CLI. It is used to install the schematics executable, which you can use to create a new schematics collection with an initial named schematic. The collection folder is a workspace for schematics. You can also use the schematics command to add a new schematic to an existing collection, or extend an existing schematic. You can install Schematic CLI globally as below,
```bash
npm install -g @angular-devkit/schematics-cli
```
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161. ### What are the best practices for security in angular?
Below are the best practices of security in angular,
1. Use the latest Angular library releases
2. Don't modify your copy of Angular
3. Avoid Angular APIs marked in the documentation as “Security Risk.”
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162. ### What is Angular security model for preventing XSS attacks?
Angular treats all values as untrusted by default. i.e, Angular sanitizes and escapes untrusted values When a value is inserted into the DOM from a template, via property, attribute, style, class binding, or interpolation.
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163. ### What is the role of template compiler for prevention of XSS attacks?
The offline template compiler prevents vulnerabilities caused by template injection, and greatly improves application performance. So it is recommended to use offline template compiler in production deployments without dynamically generating any template.
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164. ### What are the various security contexts in Angular?
Angular defines the following security contexts for sanitization,
1. **HTML:** It is used when interpreting a value as HTML such as binding to innerHtml.
2. **Style:** It is used when binding CSS into the style property.
3. **URL:** It is used for URL properties such as `<a href>`.
4. **Resource URL:** It is a URL that will be loaded and executed as code such as `<script src>`.
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165. ### What is Sanitization? Is angular supports it?
**Sanitization** is the inspection of an untrusted value, turning it into a value that's safe to insert into the DOM. Yes, Angular suppports sanitization. It sanitizes untrusted values for HTML, styles, and URLs but sanitizing resource URLs isn't possible because they contain arbitrary code.
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166. ### What is the purpose of innerHTML?
The innerHtml is a property of HTML-Elements, which allows you to set it's html-content programmatically. Let's display the below html code snippet in a `<div>` tag as below using innerHTML binding,
```html
<div [innerHTML]="htmlSnippet"></div>
```
and define the htmlSnippet property from any component
```javascript
export class myComponent {
htmlSnippet: string = '<b>Hello World</b>, Angular';
}
```
Unfortunately this property could cause Cross Site Scripting (XSS) security bugs when improperly handled.
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167. ### What is the difference between interpolated content and innerHTML?
The main difference between interpolated and innerHTML code is the behavior of code interpreted. Interpolated content is always escaped i.e, HTML isn't interpreted and the browser displays angle brackets in the element's text content. Where as in innerHTML binding, the content is interpreted i.e, the browser will convert < and > characters as HTMLEntities. For example, the usage in template would be as below,
```html
<p>Interpolated value:</p>
<div >{{htmlSnippet}}</div>
<p>Binding of innerHTML:</p>
<div [innerHTML]="htmlSnippet"></div>
```
and the property defined in a component.
```javascript
export class InnerHtmlBindingComponent {
htmlSnippet = 'Template <script>alert("XSS Attack")</script> <b>Code attached</b>';
}
```
Even though innerHTML binding create a chance of XSS attack, Angular recognizes the value as unsafe and automatically sanitizes it.
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168. ### How do you prevent automatic sanitization?
Sometimes the applications genuinely need to include executable code such as displaying `<iframe>` from an URL. In this case, you need to prevent automatic sanitization in Angular by saying that you inspected a value, checked how it was generated, and made sure it will always be secure. Basically it involves 2 steps,
1. Inject DomSanitizer: You can inject DomSanitizer in component as parameter in constructor
2. Mark the trusted value by calling some of the below methods
1. bypassSecurityTrustHtml
2. bypassSecurityTrustScript
3. bypassSecurityTrustStyle
4. bypassSecurityTrustUrl
5. bypassSecurityTrustResourceUrl
For example,The usage of dangerous url to trusted url would be as below,
```javascript
constructor(private sanitizer: DomSanitizer) {
this.dangerousUrl = 'javascript:alert("XSS attack")';
this.trustedUrl = sanitizer.bypassSecurityTrustUrl(this.dangerousUrl);
```
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169. ### Is safe to use direct DOM API methods in terms of security?
No,the built-in browser DOM APIs or methods don't automatically protect you from security vulnerabilities. In this case it is recommended to use Angular templates instead of directly interacting with DOM. If it is unavoidable then use the built-in Angular sanitization functions.
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170. ### What is DOM sanitizer?
`DomSanitizer` is used to help preventing Cross Site Scripting Security bugs (XSS) by sanitizing values to be safe to use in the different DOM contexts.
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171. ### How do you support server side XSS protection in Angular application?
The server-side XSS protection is supported in an angular application by using a templating language that automatically escapes values to prevent XSS vulnerabilities on the server. But don't use a templating language to generate Angular templates on the server side which creates a high risk of introducing template-injection vulnerabilities.
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172. ### Is angular prevents http level vulnerabilities?
Angular has built-in support for preventing http level vulnerabilities such as as cross-site request forgery (CSRF or XSRF) and cross-site script inclusion (XSSI). Even though these vulnerabilities need to be mitigated on server-side, Angular provides helpers to make the integration easier on the client side.
1. HttpClient supports a token mechanism used to prevent XSRF attacks
2. HttpClient library recognizes the convention of prefixed JSON responses(which non-executable js code with ")]}',\\n" characters) and automatically strips the string ")]}',\\n" from all responses before further parsing
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173. ### What are Http Interceptors?
Http Interceptors are part of @angular/common/http, which inspect and transform HTTP requests from your application to the server and vice-versa on HTTP responses. These interceptors can perform a variety of implicit tasks, from authentication to logging.
The syntax of HttpInterceptor interface looks like as below,
```javascript
interface HttpInterceptor {
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>>
}
```
You can use interceptors by declaring a service class that implements the intercept() method of the HttpInterceptor interface.
```javascript
@Injectable()
export class MyInterceptor implements HttpInterceptor {
constructor() {}
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
...
}
}
```
After that you can use it in your module,
```javascript
@NgModule({
...
providers: [
{
provide: HTTP_INTERCEPTORS,
useClass: MyInterceptor,
multi: true
}
]
...
})
export class AppModule {}
```
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174. ### What are the applications of HTTP interceptors?
The HTTP Interceptors can be used for different variety of tasks,
1. Authentication
2. Logging
3. Caching
4. Fake backend
5. URL transformation
6. Modifying headers
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175. ### Is multiple interceptors supported in Angular?
Yes, Angular supports multiple interceptors at a time. You could define multiple interceptors in providers property:
```javascript
providers: [
{ provide: HTTP_INTERCEPTORS, useClass: MyFirstInterceptor, multi: true },
{ provide: HTTP_INTERCEPTORS, useClass: MySecondInterceptor, multi: true }
],
```
The interceptors will be called in the order in which they were provided. i.e, MyFirstInterceptor will be called first in the above interceptors configuration.
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176. ### How can I use interceptor for an entire application?
You can use same instance of `HttpInterceptors` for the entire app by importing the `HttpClientModule` only in your AppModule, and add the interceptors to the root application injector.
For example, let's define a class that is injectable in root application.
```javascript
@Injectable()
export class MyInterceptor implements HttpInterceptor {
intercept(
req: HttpRequest<any>,
next: HttpHandler
): Observable<HttpEvent<any>> {
return next.handle(req).do(event => {
if (event instanceof HttpResponse) {
// Code goes here
}
});
}
}
```
After that import HttpClientModule in AppModule
```javascript
@NgModule({
declarations: [AppComponent],
imports: [BrowserModule, HttpClientModule],
providers: [
{ provide: HTTP_INTERCEPTORS, useClass: MyInterceptor, multi: true }
],
bootstrap: [AppComponent]
})
export class AppModule {}
```
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177. ### How does Angular simplifies Internationalization?
Angular simplifies the below areas of internationalization,
1. Displaying dates, number, percentages, and currencies in a local format.
2. Preparing text in component templates for translation.
3. Handling plural forms of words.
4. Handling alternative text.
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178. ### How do you manually register locale data?
By default, Angular only contains locale data for en-US which is English as spoken in the United States of America . But if you want to set to another locale, you must import locale data for that new locale. After that you can register using `registerLocaleData` method and the syntax of this method looks like below,
```javascript
registerLocaleData(data: any, localeId?: any, extraData?: any): void
```
For example, let us import German locale and register it in the application
```javascript
import { registerLocaleData } from '@angular/common';
import localeDe from '@angular/common/locales/de';
registerLocaleData(localeDe, 'de');
```
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179. ### What are the four phases of template translation?
The i18n template translation process has four phases:
1. **Mark static text messages in your component templates for translation:** You can place i18n on every element tag whose fixed text is to be translated. For example, you need i18n attribue for heading as below,
```javascript
<h1 i18n>Hello i18n!</h1>
```
2. **Create a translation file:** Use the Angular CLI xi18n command to extract the marked text into an industry-standard translation source file. i.e, Open terminal window at the root of the app project and run the CLI command xi18n.
```bash
ng xi18n
```
The above command creates a file named `messages.xlf` in your project's root directory.
**Note:** You can supply command options to change the format, the name, the location, and the source locale of the extracted file.
3. **Edit the generated translation file:** Translate the extracted text into the target language. In this step, create a localization folder (such as `locale`)under root directory(src) and then create target language translation file by copying and renaming the default messages.xlf file. You need to copy source text node and provide the translation under target tag.
For example, create the translation file(messages.de.xlf) for German language
```javascript
<trans-unit id="greetingHeader" datatype="html">
<source>Hello i18n!</source>
<target>Hallo i18n !</target>
<note priority="1" from="description">A welcome header for this sample</note>
<note priority="1" from="meaning">welcome message</note>
</trans-unit>
```
4. **Merge the completed translation file into the app:** You need to use Angular CLI build command to compile the app, choosing a locale-specific configuration, or specifying the following command options.
1. --i18nFile=path to the translation file
2. --i18nFormat=format of the translation file
3. --i18nLocale= locale id
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180. ### What is the purpose of i18n attribute?
The Angular i18n attribute marks translatable content. It is a custom attribute, recognized by Angular tools and compilers. The compiler removes it after translation.
**Note:** Remember that i18n is not an Angular directive.
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181. ### What is the purpose of custom id?
When you change the translatable text, the Angular extractor tool generates a new id for that translation unit. Because of this behavior, you must then update the translation file with the new id every time.
For example, the translation file `messages.de.xlf.html` has generated trans-unit for some text message as below
```html
<trans-unit id="827wwe104d3d69bf669f823jjde888" datatype="html">
```
You can avoid this manual update of `id` attribute by specifying a custom id in the i18n attribute by using the prefix @@.
```javascript
<h1 i18n="@@welcomeHeader">Hello i18n!</h1>
```
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182. ### What happens if the custom id is not unique?
You need to define custom ids as unique. If you use the same id for two different text messages then only the first one is extracted. But its translation is used in place of both original text messages.
For example, let's define same custom id `myCustomId` for two messages,
```html
<h2 i18n="@@myCustomId">Good morning</h3>
<!-- ... -->
<h2 i18n="@@myCustomId">Good night</p>
```
and the translation unit generated for first text in for German language as
```html
<trans-unit id="myId" datatype="html">
<source>Good morning</source>
<target state="new">Guten Morgen</target>
</trans-unit>
```
Since custom id is the same, both of the elements in the translation contain the same text as below
```html
<h2>Guten Morgen</h2>
<h2>Guten Morgen</h2>
```
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183. ### Can I translate text without creating an element?
Yes, you can achieve using `<ng-container>` attribute. Normally you need to wrap a text content with i18n attribute for the translation. But if you don't want to create a new DOM element just for the sake of translation, you can wrap the text in an <ng-container> element.
```html
<ng-container i18n>I'm not using any DOM element for translation</ng-container>
```
Remember that `<ng-container>` is transformed into an html comment
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184. ### How can I translate attribute?
You can translate attributes by attaching `i18n-x` attribute where x is the name of the attribute to translate. For example, you can translate image title attribute as below,
```html
<img [src]="example" i18n-title title="Internationlization" />
```
By the way, you can also assign meaning, description and id with the i18n-x="<meaning>|<description>@@<id>" syntax.
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185. ### List down the pluralization categories?
Pluralization has below categories depending on the language.
1. =0 (or any other number)
2. zero
3. one
4. two
5. few
6. many
7. other
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186. ### What is select ICU expression?
ICU expression is is similar to the plural expressions except that you choose among alternative translations based on a string value instead of a number. Here you define those string values.
Let's take component binding with `residenceStatus` property which has "citizen", "permanent resident" and "foreigner" possible values and the message maps those values to the appropriate translations.
```javascript
<span i18n>The person is {residenceStatus, select, citizen {citizen} permanent resident {permanentResident} foreigner {foreigner}}</span>
```
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187. ### How do you report missing translations?
By default, When translation is missing, it generates a warning message such as "Missing translation for message 'somekey'". But you can configure with a different level of message in Angular compiler as below,
1. **Error:** It throws an error. If you are using AOT compilation, the build will fail. But if you are using JIT compilation, the app will fail to load.
2. **Warning (default):** It shows a 'Missing translation' warning in the console or shell.
3. **Ignore:** It doesn't do anything.
If you use AOT compiler then you need to perform changes in `configurations` section of your Angular CLI configuration file, angular.json.
```javascript
"configurations": {
...
"de": {
...
"i18nMissingTranslation": "error"
}
}
```
If you use the JIT compiler, specify the warning level in the compiler config at bootstrap by adding the 'MissingTranslationStrategy' property as below,
```javascript
import { MissingTranslationStrategy } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app/app.module';
platformBrowserDynamic().bootstrapModule(AppModule, {
missingTranslation: MissingTranslationStrategy.Error,
providers: [
// ...
]
});
```
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188. ### How do you provide build configuration for multiple locales?
You can provide build configuration such as translation file path, name, format and application url in `configuration` settings of Angular.json file. For example, the German version of your application configured the build as follows,
```javascript
"configurations": {
"de": {
"aot": true,
"outputPath": "dist/my-project-de/",
"baseHref": "/fr/",
"i18nFile": "src/locale/messages.de.xlf",
"i18nFormat": "xlf",
"i18nLocale": "de",
"i18nMissingTranslation": "error",
}
```
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189. ### What is an angular library?
An Angular library is an Angular project that differs from an app in that it cannot run on its own. It must be imported and used in an app. For example, you can import or add `service worker` library to an Angular application which turns an application into a Progressive Web App (PWA).
**Note:** You can create own third party library and publish it as npm package to be used in an Application.
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190. ### What is AOT compiler?
The AOT compiler is part of a build process that produces a small, fast, ready-to-run application package, typically for production. It converts your Angular HTML and TypeScript code into efficient JavaScript code during the build phase before the browser downloads and runs that code.
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191. ### How do you select an element in component template?
You can control any DOM element via ElementRef by injecting it into your component's constructor. i.e, The component should have constructor with ElementRef parameter,
```javascript
constructor(myElement: ElementRef) {
el.nativeElement.style.backgroundColor = 'yellow';
}
```
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192. ### What is TestBed?
TestBed is an api for writing unit tests for Angular applications and it's libraries. Even though We still write our tests in Jasmine and run using Karma, this API provides an easier way to create components, handle injection, test asynchronous behaviour and interact with our application.
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193. ### What is protractor?
Protractor is an end-to-end test framework for Angular and AngularJS applications. It runs tests against your application running in a real browser, interacting with it as a user would.
```javascript
npm install -g protractor
```
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194. ### What is collection?
Collection is a set of related schematics collected in an npm package. For example, `@schematics/angular` collection is used in Angular CLI to apply transforms to a web-app project. You can create your own schematic collection for customizing angular projects.
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195. ### How do you create schematics for libraries?
You can create your own schematic collections to integrate your library with the Angular CLI. These collections are classified as 3 main schematics,
1. **Add schematics:** These schematics are used to install library in an Angular workspace using `ng add` command.
For example, @angular/material schematic tells the add command to install and set up Angular Material and theming.
2. **Generate schematics**: These schematics are used to modify projects, add configurations and scripts, and scaffold artifacts in library using `ng generate` command.
For example, @angular/material generation schematic supplies generation schematics for the UI components. Let's say the table component is generated using `ng generate @angular/material:table `.
3. **Update schematics:** These schematics are used to update library's dependencies and adjust for breaking changes in a new library release using `ng update` command.
For example, @angular/material update schematic updates material and cdk dependencies using `ng update @angular/material` command.
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196. ### How do you use jquery in Angular?
You can use jquery in Angular using 3 simple steps,
1. **Install the dependency:** At first, install the jquery dependency using npm
```cmd
npm install --save jquery
```
2. **Add the jquery script:** In Angular-CLI project, add the relative path to jquery in the angular.json file.
```javascript
"scripts": [
"node_modules/jquery/dist/jquery.min.js"
]
```
3. **Start using jquery:** Define the element in template. Whereas declare the jquery variable and apply CSS classes on the element.
```html
<div id="elementId">
<h1>JQuery integration</h1>
</div>
```
```javascript
import {Component, OnInit} from '@angular/core';
declare var $: any; // (or) import * as $ from 'jquery';
@Component({
selector: 'app-root',
templateUrl: './app.component.html',
styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
ngOnInit(): void {
$(document).ready(() => {
$('#elementId').css({'text-color': 'blue', 'font-size': '150%'});
});
}
}
```
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197. ### What is the reason for No provider for HTTP exception?
This exception is due to missing HttpClientModule in your module. You just need to import in module as below,
```javascript
import { HttpClientModule } from '@angular/common/http';
@NgModule({
imports: [
BrowserModule,
HttpClientModule,
],
declarations: [ AppComponent ],
bootstrap: [ AppComponent ]
})
export class AppModule { }
```
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198. ### What is router state?
The RouteState is an interface which represents the state of the router as a tree of activated routes.
```javascript
interface RouterState extends Tree {
snapshot: RouterStateSnapshot
toString(): string
}
```
You can access the current RouterState from anywhere in the Angular app using the Router service and the routerState property.
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199. ### How can I use SASS in angular project?
When you are creating your project with angular cli, you can use `ng new`command. It generates all your components with predefined sass files.
```javascript
ng new My_New_Project --style=sass
```
But if you are changing your existing style in your project then use `ng set` command,
```javascript
ng set defaults.styleExt scss
```
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200. ### What is the purpose of hidden property?
The hidden property is used to show or hide the associated DOM element, based on an expression. It can be compared close to `ng-show` directive in AngularJS. Let's say you want to show user name based on the availability of user using `hidden` property.
```javascript
<div [hidden]="!user.name">
My name is: {{user.name}}
</div>
```
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201. ### What is the difference between ngIf and hidden property?
The main difference is that *ngIf will remove the element from the DOM, while [hidden] actually plays with the CSS style by setting `display:none`. Generally it is expensive to add and remove stuff from the DOM for frequent actions.
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202. ### What is slice pipe?
The slice pipe is used to create a new Array or String containing a subset (slice) of the elements. The syntax looks like as below,
```javascript
{{ value_expression | slice : start [ : end ] }}
```
For example, you can provide 'hello' list based on a greeting array,
```javascript
@Component({
selector: 'list-pipe',
template: `<ul>
<li *ngFor="let i of greeting | slice:0:5">{{i}}</li>
</ul>`
})
export class PipeListComponent {
greeting: string[] = ['h', 'e', 'l', 'l', 'o', 'm','o', 'r', 'n', 'i', 'n', 'g'];
}
```
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203. ### What is index property in ngFor directive?
The index property of the NgFor directive is used to return the zero-based index of the item in each iteration. You can capture the index in a template input variable and use it in the template.
For example, you can capture the index in a variable named indexVar and displays it with the todo's name using ngFor directive as below.
```javascript
<div *ngFor="let todo of todos; let i=index">{{i + 1}} - {{todo.name}}</div>
```
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204. ### What is the purpose of ngFor trackBy?
The main purpose of using *ngFor with trackBy option is performance optimization. Normally if you use NgFor with large data sets, a small change to one item by removing or adding an item, can trigger a cascade of DOM manipulations. In this case, Angular sees only a fresh list of new object references and to replace the old DOM elements with all new DOM elements. You can help Angular to track which items added or removed by providing a `trackBy` function which takes the index and the current item as arguments and needs to return the unique identifier for this item.
For example, lets set trackBy to the trackByTodos() method
```javascript
<div *ngFor="let todo of todos; trackBy: trackByTodos">
({{todo.id}}) {{todo.name}}
</div>
```
and define the trackByTodos method,
```javascript
trackByTodos(index: number, item: Todo): number { return todo.id; }
```
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205. ### What is the purpose of ngSwitch directive?
**NgSwitch** directive is similar to JavaScript switch statement which displays one element from among several possible elements, based on a switch condition. In this case only the selected element placed into the DOM. It has been used along with `NgSwitch`, `NgSwitchCase` and `NgSwitchDefault` directives.
For example, let's display the browser details based on selected browser using ngSwitch directive.
```javascript
<div [ngSwitch]="currentBrowser.name">
<chrome-browser *ngSwitchCase="'chrome'" [item]="currentBrowser"></chrome-browser>
<firefox-browser *ngSwitchCase="'firefox'" [item]="currentBrowser"></firefox-browser>
<opera-browser *ngSwitchCase="'opera'" [item]="currentBrowser"></opera-browser>
<safari-browser *ngSwitchCase="'safari'" [item]="currentBrowser"></safari-browser>
<ie-browser *ngSwitchDefault [item]="currentItem"></ie-browser>
</div>
```
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206. ### Is it possible to do aliasing for inputs and outputs?
Yes, it is possible to do aliasing for inputs and outputs in two ways.
1. **Aliasing in metadata:** The inputs and outputs in the metadata aliased using a colon-delimited (:) string with the directive property name on the left and the public alias on the right. i.e. It will be in the format of propertyName:alias.
```javascript
inputs: ['input1: buyItem'],
outputs: ['outputEvent1: completedEvent']
```
2. **Aliasing with @Input()/@Output() decorator:** The alias can be specified for the property name by passing the alias name to the @Input()/@Output() decorator.i.e. It will be in the form of @Input(alias) or @Output(alias).
```javascript
@Input('buyItem') input1: string;
@Output('completedEvent') outputEvent1 = new EventEmitter<string>();
```
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207. ### What is safe navigation operator?
The safe navigation operator(?)(or known as Elvis Operator) is used to guard against `null` and `undefined` values in property paths when you are not aware whether a path exists or not. i.e. It returns value of the object path if it exists, else it returns the null value.
For example, you can access nested properties of a user profile easily without null reference errors as below,
```javascript
<p>The user firstName is: {{user?.fullName.firstName}}</p>
```
Using this safe navigation operator, Angular framework stops evaluating the expression when it hits the first null value and renders the view without any errors.
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208. ### Is any special configuration required for Angular9?
You don't need any special configuration. In Angular9, the Ivy renderer is the default Angular compiler. Even though Ivy is available Angular8 itself, you had to configure it in tsconfig.json file as below,
```javascript
"angularCompilerOptions": { "enableIvy": true }
```
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209. ### What are type safe TestBed API changes in Angular9?
Angular 9 provides type safe changes in TestBed API changes by replacing the old get function with the new inject method. Because TestBed.get method is not type-safe. The usage would be as below,
```javascript
TestBed.get(ChangeDetectorRef) // returns any. It is deprecated now.
TestBed.inject(ChangeDetectorRef) // returns ChangeDetectorRef
```
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210. ### Is mandatory to pass static flag for ViewChild?
In Angular 8, the static flag is required for ViewChild. Whereas in Angular9, you no longer need to pass this property. Once you updated to Angular9 using `ng update`, the migration will remove { static: false } script everywhere.
```javascript
@ViewChild(ChildDirective) child: ChildDirective; // Angular9 usage
@ViewChild(ChildDirective, { static: false }) child: ChildDirective; //Angular8 usage
```
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211. ### What are the list of template expression operators?
The Angular template expression language supports three special template expression operators.
1. Pipe operator
2. Safe navigation operator
3. Non-null assertion operator
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212. ### What is the precedence between pipe and ternary operators?
The pipe operator has a higher precedence than the ternary operator (?:). For example, the expression `first ? second : third | fourth` is parsed as `first ? second : (third | fourth)`.
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213. ### What is an entry component?
An entry component is any component that Angular loads imperatively(i.e, not referencing it in the template) by type. Due to this behavior, they can’t be found by the Angular compiler during compilation. These components created dynamically with `ComponentFactoryResolver`.
Basically, there are two main kinds of entry components which are following -
1. The bootstrapped root component
2. A component you specify in a route
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214. ### What is a bootstrapped component?
A bootstrapped component is an entry component that Angular loads into the DOM during the bootstrap process or application launch time. Generally, this bootstrapped or root component is named as `AppComponent` in your root module using `bootstrap` property as below.
```js
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
FormsModule,
HttpClientModule,
AppRoutingModule
],
providers: [],
bootstrap: [AppComponent] // bootstrapped entry component need to be declared here
})
```
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215. ### How do you manually bootstrap an application?
You can use `ngDoBootstrap` hook for a manual bootstrapping of the application instead of using bootstrap array in `@NgModule` annotation. This hook is part of `DoBootstap` interface.
```js
interface DoBootstrap {
ngDoBootstrap(appRef: ApplicationRef): void
}
```
The module needs to be implement the above interface to use the hook for bootstrapping.
```js
class AppModule implements DoBootstrap {
ngDoBootstrap(appRef: ApplicationRef) {
appRef.bootstrap(AppComponent); // bootstrapped entry component need to be passed
}
}
```
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216. ### Is it necessary for bootstrapped component to be entry component?
Yes, the bootstrapped component needs to be an entry component. This is because the bootstrapping process is an imperative process.
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217. ### What is a routed entry component?
The components referenced in router configuration are called as routed entry components. This routed entry component defined in a route definition as below,
```js
const routes: Routes = [
{
path: '',
component: TodoListComponent // router entry component
}
];
```
Since router definition requires you to add the component in two places (router and entryComponents), these components are always entry components.
**Note:** The compilers are smart enough to recognize a router definition and automatically add the router component into `entryComponents`.
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218. ### Why is not necessary to use entryComponents array every time?
Most of the time, you don't need to explicity to set entry components in entryComponents array of ngModule decorator. Because angular adds components from both @NgModule.bootstrap and route definitions to entry components automatically.
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219. ### Do I still need to use entryComponents array in Angular9?
No. In previous angular releases, the entryComponents array of ngModule decorator is used to tell the compiler which components would be created and inserted dynamically in the view. In Angular9, this is not required anymore with Ivy.
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220. ### Is it all components generated in production build?
No, only the entry components and template components appears in production builds. If a component isn't an entry component and isn't found in a template, the tree shaker will throw it away. Due to this reason, make sure to add only true entry components to reduce the bundle size.
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221. ### What is Angular compiler?
The Angular compiler is used to convert the application code into JavaScript code. It reads the template markup, combines it with the corresponding component class code, and emits component factories which creates JavaScript representation of the component along with elements of @Component metadata.
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222. ### What is the role of ngModule metadata in compilation process?
The `@NgModule` metadata is used to tell the Angular compiler what components to be compiled for this module and how to link this module with other modules.
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223. ### How does angular finds components, directives and pipes?
The Angular compiler finds a component or directive in a template when it can match the selector of that component or directive in that template. Whereas it finds a pipe if the pipe's name appears within the pipe syntax of the template HTML.
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224. ### Give few examples for NgModules?
The Angular core libraries and third-party libraries are available as NgModules.
1. Angular libraries such as FormsModule, HttpClientModule, and RouterModule are NgModules.
2. Many third-party libraries such as Material Design, Ionic, and AngularFire2 are NgModules.
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225. ### What are feature modules?
Feature modules are NgModules, which are used for the purpose of organizing code. The feature module can be created with Angular CLI using the below command in the root directory,
```javascript
ng generate module MyCustomFeature //
```
Angular CLI creates a folder called `my-custom-feature` with a file inside called `my-custom-feature.module.ts` with the following contents
```javascript
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
@NgModule({
imports: [
CommonModule
],
declarations: []
})
export class MyCustomFeature { }
```
**Note:** The "Module" suffix shouldn't present in the name because the CLI appends it.
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226. ### What are the imported modules in CLI generated feature modules?
In the CLI generated feature module, there are two JavaScript import statements at the top of the file
1. **NgModule:** InOrder to use the `@NgModule` decorator
2. **CommonModule:** It provides many common directives such as `ngIf` and `ngFor`.
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227. ### What are the differences between ngmodule and javascript module?
Below are the main differences between Angular NgModule and javascript module,
| NgModule | JavaScript module |
|---- | --------- |
| NgModule bounds declarable classes only | There is no restriction classes |
| List the module's classes in declarations array only | Can define all member classes in one giant file |
| It only export the declarable classes it owns or imports from other modules| It can export any classes |
| Extend the entire application with services by adding providers to provides array | Can't extend the application with services |
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228. ### What are the possible errors with declarations?
There are two common possible errors with declarations array,
1. If you use a component without declaring it, Angular returns an error message.
2. If you try to declare the same class in more than one module then compiler emits an error.
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229. ### What are the steps to use declaration elements?
Below are the steps to be followed to use declaration elements.
1. Create the element(component, directive and pipes) and export it from the file where you wrote it
2. Import it into the appropriate module.
3. Declare it in the @NgModule declarations array.
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230. ### What happens if browserModule used in feature module?
If you do import `BrowserModule` into a lazy loaded feature module, Angular returns an error telling you to use `CommonModule` instead. Because BrowserModule’s providers are for the entire app so it should only be in the root module, not in feature module. Whereas Feature modules only need the common directives in CommonModule.
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231. ### What are the types of feature modules?
Below are the five categories of feature modules,
1. **Domain:** Deliver a user experience dedicated to a particular application domain(For example, place an order, registration etc)
2. **Routed:** These are domain feature modules whose top components are the targets of router navigation routes.
3. **Routing:** It provides routing configuration for another module.
4. **Service:** It provides utility services such as data access and messaging(For example, HttpClientModule)
5. **Widget:** It makes components, directives, and pipes available to external modules(For example, third-party libraries such as Material UI)
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232. ### What is a provider?
A provider is an instruction to the Dependency Injection system on how to obtain a value for a dependency(aka services created). The service can be provided using Angular CLI as below,
```javascript
ng generate service my-service
```
The created service by CLI would be as below,
```js
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root', //Angular provide the service in root injector
})
export class MyService {
}
```
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233. ### What is the recommendation for provider scope?
You should always provide your service in the root injector unless there is a case where you want the service to be available only if you import a particular @NgModule.
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234. ### How do you restrict provider scope to a module?
It is possible to restrict service provider scope to a specific module instead making available to entire application. There are two possible ways to do it.
1. **Using providedIn in service:**
```js
import { Injectable } from '@angular/core';
import { SomeModule } from './some.module';
@Injectable({
providedIn: SomeModule,
})
export class SomeService {
}
```
2. **Declare provider for the service in module:**
```js
import { NgModule } from '@angular/core';
import { SomeService } from './some.service';
@NgModule({
providers: [SomeService],
})
export class SomeModule {
}
```
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235. ### How do you provide a singleton service?
There are two possible ways to provide a singleton service.
1. Set the providedIn property of the @Injectable() to "root". This is the preferred way(starting from Angular 6.0) of creating a singleton service since it makes your services tree-shakable.
```js
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class MyService {
}
```
2. Include the service in root module or in a module that is only imported by root module. It has been used to register services before Angular 6.0.
```js
@NgModule({
...
providers: [MyService],
...
})
```
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236. ### What are the different ways to remove duplicate service registration?
If a module defines provides and declarations then loading the module in multiple feature modules will duplicate the registration of the service. Below are the different ways to prevent this duplicate behavior.
1. Use the providedIn syntax instead of registering the service in the module.
2. Separate your services into their own module.
3. Define forRoot() and forChild() methods in the module.
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237. ### How does forRoot method helpful to avoid duplicate router instances?
If the `RouterModule` module didn’t have forRoot() static method then each feature module would instantiate a new Router instance, which leads to broken application due to duplicate instances. After using forRoot() method, the root application module imports `RouterModule.forRoot(...)` and gets a Router, and all feature modules import `RouterModule.forChild(...)` which does not instantiate another Router.
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238. ### What is a shared module?
The Shared Module is the module in which you put commonly used directives, pipes, and components into one module that is shared(import it) throughout the application.
For example, the below shared module imports CommonModule, FormsModule for common directives and components, pipes and directives based on the need,
```js
import { CommonModule } from '@angular/common';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { UserComponent } from './user.component';
import { NewUserDirective } from './new-user.directive';
import { OrdersPipe } from './orders.pipe';
@NgModule({
imports: [ CommonModule ],
declarations: [ UserComponent, NewUserDirective, OrdersPipe ],
exports: [ UserComponent, NewUserDirective, OrdersPipe,
CommonModule, FormsModule ]
})
export class SharedModule { }
```
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239. ### Can I share services using modules?
No, it is not recommended to share services by importing module. i.e Import modules when you want to use directives, pipes, and components only. The best approach to get a hold of shared services is through 'Angular dependency injection' because importing a module will result in a new service instance.
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240. ### How do you get current direction for locales?
In Angular 9.1, the API method `getLocaleDirection` can be used to get the current direction in your app. This method is useful to support Right to Left locales for your Internationalization based applications.
```js
import { getLocaleDirection, registerLocaleData } from '@angular/common';
import { LOCALE_ID } from '@angular/core';
import localeAr from '@angular/common/locales/ar';
...
constructor(@Inject(LOCALE_ID) locale) {
const directionForLocale = getLocaleDirection(locale); // Returns 'rtl' or 'ltr' based on the current locale
registerLocaleData(localeAr, 'ar-ae');
const direction = getLocaleDirection('ar-ae'); // Returns 'rtl'
// Current direction is used to provide conditional logic here
}
```
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241. ### What is ngcc?
The ngcc(Angular Compatibility Compiler) is a tool which upgrades node_module compiled with non-ivy ngc into ivy compliant format. The `postinstall` script from package.json will make sure your node_modules will be compatible with the Ivy renderer.
```js
"scripts": {
"postinstall": "ngcc"
}
```
Whereas, Ivy compiler (ngtsc), which compiles Ivy-compatible code.
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242. ### What classes should not be added to declarations?
The below class types shouldn't be added to declarations
1. A class which is already declared in any another module.
2. Directives imported from another module.
3. Module classes.
4. Service classes.
5. Non-Angular classes and objects, such as strings, numbers, functions, entity models, configurations, business logic, and helper classes.
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243. ### What is NgZone?
Angular provides a service called NgZone which creates a zone named `angular` to automatically trigger change detection when the following conditions are satisfied.
1. When a sync or async function is executed.
2. When there is no microTask scheduled.
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244. ### What is NoopZone?
Zone is loaded/required by default in Angular applications and it helps Angular to know when to trigger the change detection. This way, it make sures developers focus on application development rather core part of Angular. You can also use Angular without Zone but the change detection need to be implemented on your own and `noop zone` need to be configured in bootstrap process.
Let's follow the below two steps to remove zone.js,
1. Remove the zone.js import from polyfills.ts.
```js
/***************************************************************************************************
* Zone JS is required by default for Angular itself.
*/
// import 'zone.js/dist/zone'; // Included with Angular CLI.
```
2. Bootstrap Angular with noop zone in src/main.ts.
```js
platformBrowserDynamic().bootstrapModule(AppModule, {ngZone: 'noop'})
.catch(err => console.error(err));
```
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245. ### How do you create displayBlock components?
By default, Angular CLI creates components in an inline displayed mode(i.e, display:inline). But it is possible to create components with display: block style using `displayBlock` option,
```js
ng generate component my-component --displayBlock
```
(OR) the option can be turned on by default in Angular.json with `schematics.@schematics/angular:component.displayBlock` key value as true.
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246. ### What are the possible data update scenarios for change detection?
The change detection works in the following scenarios where the data changes needs to update the application HTML.
1. **Component initialization:** While bootstrapping the Angular application, Angular triggers the `ApplicationRef.tick()` to call change detection and View Rendering.
2. **Event listener:** The DOM event listener can update the data in an Angular component and trigger the change detection too.
```js
@Component({
selector: 'app-event-listener',
template: `
<button (click)="onClick()">Click</button>
{{message}}`
})
export class EventListenerComponent {
message = '';
onClick() {
this.message = 'data updated';
}
}
```
3. **HTTP Data Request:** You can get data from a server through an HTTP request
```js
data = 'default value';
constructor(private httpClient: HttpClient) {}
ngOnInit() {
this.httpClient.get(this.serverUrl).subscribe(response => {
this.data = response.data; // change detection will happen automatically
});
}
```
4. **Macro tasks setTimeout() or setInterval():** You can update the data in the callback function of setTimeout or setInterval
```js
data = 'default value';
ngOnInit() {
setTimeout(() => {
this.data = 'data updated'; // Change detection will happen automatically
});
}
```
5. **Micro tasks Promises:** You can update the data in the callback function of promise
```js
data = 'initial value';
ngOnInit() {
Promise.resolve(1).then(v => {
this.data = v; // Change detection will happen automatically
});
}
```
6. **Async operations like Web sockets and Canvas:** The data can be updated asynchronously using WebSocket.onmessage() and Canvas.toBlob().
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247. ### What is a zone context?
Execution Context is an abstract concept that holds information about the environment within the current code being executed. A zone provides an execution context that persists across asynchronous operations is called as zone context. For example, the zone context will be same in both outside and inside setTimeout callback function,
```js
zone.run(() => {
// outside zone
expect(zoneThis).toBe(zone);
setTimeout(function() {
// the same outside zone exist here
expect(zoneThis).toBe(zone);
});
});
```
The current zone is retrieved through `Zone.current`.
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248. ### What are the lifecycle hooks of a zone?
There are four lifecycle hooks for asynchronous operations from zone.js.
1. **onScheduleTask:** This hook triggers when a new asynchronous task is scheduled. For example, when you call setTimeout()
```js
onScheduleTask: function(delegate, curr, target, task) {
console.log('new task is scheduled:', task.type, task.source);
return delegate.scheduleTask(target, task);
}
```
2. **onInvokeTask:** This hook triggers when an asynchronous task is about to execute. For example, when the callback of setTimeout() is about to execute.
```js
onInvokeTask: function(delegate, curr, target, task, applyThis, applyArgs) {
console.log('task will be invoked:', task.type, task.source);
return delegate.invokeTask(target, task, applyThis, applyArgs);
}
```
3. **onHasTask:** This hook triggers when the status of one kind of task inside a zone changes from stable(no tasks in the zone) to unstable(a new task is scheduled in the zone) or from unstable to stable.
```js
onHasTask: function(delegate, curr, target, hasTaskState) {
console.log('task state changed in the zone:', hasTaskState);
return delegate.hasTask(target, hasTaskState);
}
```
4. **onInvoke:** This hook triggers when a synchronous function is going to execute in the zone.
```js
onInvoke: function(delegate, curr, target, callback, applyThis, applyArgs) {
console.log('the callback will be invoked:', callback);
return delegate.invoke(target, callback, applyThis, applyArgs);
}
```
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249. ### What are the methods of NgZone used to control change detection?
NgZone service provides a `run()` method that allows you to execute a function inside the angular zone. This function is used to execute third party APIs which are not handled by Zone and trigger change detection automatically at the correct time.
```js
export class AppComponent implements OnInit {
constructor(private ngZone: NgZone) {}
ngOnInit() {
// use ngZone.run() to make the asynchronous operation in the angular zone
this.ngZone.run(() => {
someNewAsyncAPI(() => {
// update the data of the component
});
});
}
}
```
Whereas `runOutsideAngular()` method is used when you don't want to trigger change detection.
```js
export class AppComponent implements OnInit {
constructor(private ngZone: NgZone) {}
ngOnInit() {
// Use this method when you know no data will be updated
this.ngZone.runOutsideAngular(() => {
setTimeout(() => {
// update component data and don't trigger change detection
});
});
}
}
```
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250. ### How do you change the settings of zonejs?
You can change the settings of zone by configuring them in a separate file and import it just after zonejs import.
For example, you can disable the requestAnimationFrame() monkey patch to prevent change detection for no data update as one setting and prevent DOM events(a mousemove or scroll event) to trigger change detection. Let's say the new file named zone-flags.js,
```js
// disable patching requestAnimationFrame
(window as any).__Zone_disable_requestAnimationFrame = true;
// disable patching specified eventNames
(window as any).__zone_symbol__UNPATCHED_EVENTS = ['scroll', 'mousemove'];
```
The above configuration file can be imported in a polyfill.ts file as below,
```js
/***************************************************************************************************
* Zone JS is required by default for Angular.
*/
import `./zone-flags`;
import 'zone.js/dist/zone'; // Included with Angular CLI.
```
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251. ### How do you trigger an animation?
Angular provides a `trigger()` function for animation in order to collect the states and transitions with a specific animation name, so that you can attach it to the triggering element in the HTML template. This function watch for changes and trigger initiates the actions when a change occurs.
For example, let's create trigger named `upDown`, and attach it to the button element.
```js
content_copy
@Component({
selector: 'app-up-down',
animations: [
trigger('upDown', [
state('up', style({
height: '200px',
opacity: 1,
backgroundColor: 'yellow'
})),
state('down', style({
height: '100px',
opacity: 0.5,
backgroundColor: 'green'
})),
transition('up => down', [
animate('1s')
]),
transition('down => up', [
animate('0.5s')
]),
]),
],
templateUrl: 'up-down.component.html',
styleUrls: ['up-down.component.css']
})
export class UpDownComponent {
isUp = true;
toggle() {
this.isUp = !this.isUp;
}
```
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252. ### How do you configure injectors with providers at different levels?
You can configure injectors with providers at different levels of your application by setting a metadata value. The configuration can happen in one of three places,
1. In the `@Injectable()` decorator for the service itself
2. In the `@NgModule()` decorator for an NgModule
3. In the `@Component()` decorator for a component
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253. ### Is it mandatory to use injectable on every service class?
No. The `@Injectable()` decorator is not strictly required if the class has other Angular decorators on it or does not have any dependencies. But the important thing here is any class that is going to be injected with Angular is decorated.
i.e, If we add the decorator, the metadata `design:paramtypes` is added, and the dependency injection can do it's job. That is the exact reason to add the @Injectable() decorator on a service if this service has some dependencies itself.
For example, Let's see the different variations of AppService in a root component,
1. The below AppService can be injected in AppComponent without any problems. This is because there are no dependency services inside AppService.
```js
export class AppService {
constructor() {
console.log('A new app service');
}
}
```
2. The below AppService with dummy decorator and httpService can be injected in AppComponent without any problems. This is because meta information is generated with dummy decorator.
```js
function SomeDummyDecorator() {
return (constructor: Function) => console.log(constructor);
}
@SomeDummyDecorator()
export class AppService {
constructor(http: HttpService) {
console.log(http);
}
}
```
and the generated javascript code of above service has meta information about HttpService,
```js
var AppService = (function () {
function AppService(http) {
console.log(http);
}
AppService = __decorate([
core_1.Injectable(),
__metadata('design:paramtypes', [http_service_1.HttpService])
], AppService);
return AppService;
}());
exports.AppService = AppService;
```
3. The below AppService with @injectable decorator and httpService can be injected in AppComponent without any problems. This is because meta information is generated with Injectable decorator.
```js
@Injectable({
providedIn: 'root',
})
export class AppService {
constructor(http: HttpService) {
console.log(http);
}
}
```
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254. ### What is an optional dependency?
The optional dependency is a parameter decorator to be used on constructor parameters, which marks the parameter as being an optional dependency. Due to this, the DI framework provides null if the dependency is not found.
For example, If you don't register a logger provider anywhere, the injector sets the value of logger(or logger service) to null in the below class.
```js
import { Optional } from '@angular/core';
constructor(@Optional() private logger?: Logger) {
if (this.logger) {
this.logger.log('This is an optional dependency message');
} else {
console.log('The logger is not registered');
}
}
```
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255. ### What are the types of injector hierarchies?
There are two types of injector hierarchies in Angular
1. **ModuleInjector hierarchy:** It configure on a module level using an @NgModule() or @Injectable() annotation.
2. **ElementInjector hierarchy:** It created implicitly at each DOM element. Also it is empty by default unless you configure it in the providers property on @Directive() or @Component().
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256. ### What are reactive forms?
Reactive forms is a model-driven approach for creating forms in a reactive style(form inputs changes over time). These are built around observable streams, where form inputs and values are provided as streams of input values. Let's follow the below steps to create reactive forms,
1. Register the reactive forms module which declares reactive-form directives in your app
```js
import { ReactiveFormsModule } from '@angular/forms';
@NgModule({
imports: [
// other imports ...
ReactiveFormsModule
],
})
export class AppModule { }
```
2. Create a new FormControl instance and save it in the component.
```js
import { Component } from '@angular/core';
import { FormControl } from '@angular/forms';
@Component({
selector: 'user-profile',
styleUrls: ['./user-profile.component.css']
})
export class UserProfileComponent {
userName = new FormControl('');
}
```
3. Register the FormControl in the template.
```js
<label>
User name:
<input type="text" [formControl]="userName">
</label>
```
Finally, the component with reactive form control appears as below,
```js
import { Component } from '@angular/core';
import { FormControl } from '@angular/forms';
@Component({
selector: 'user-profile',
styleUrls: ['./user-profile.component.css'],
template: `
<label>
User name:
<input type="text" [formControl]="userName">
</label>
`
})
export class UserProfileComponent {
userName = new FormControl('');
}
```
**[⬆ Back to Top](#table-of-contents)**
257. ### What are dynamic forms?
Dynamic forms is a pattern in which we build a form dynamically based on metadata that describes a business object model. You can create them based on reactive form API.
**[⬆ Back to Top](#table-of-contents)**
258. ### What are template driven forms?
Template driven forms are model-driven forms where you write the logic, validations, controls etc, in the template part of the code using directives. They are suitable for simple scenarios and uses two-way binding with [(ngModel)] syntax.
For example, you can create register form easily by following the below simple steps,
1. Import the FormsModule into the Application module's imports array
```js
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import {FormsModule} from '@angular/forms'
import { RegisterComponent } from './app.component';
@NgModule({
declarations: [
RegisterComponent,
],
imports: [
BrowserModule,
FormsModule
],
providers: [],
bootstrap: [RegisterComponent]
})
export class AppModule { }
```
2. Bind the form from template to the component using ngModel syntax
```html
<input type="text" class="form-control" id="name"
required
[(ngModel)]="model.name" name="name">
```
3. Attach NgForm directive to the <form> tag in order to create FormControl instances and register them
```js
<form #registerForm="ngForm">
```
4. Apply the validation message for form controls
```html
<label for="name">Name</label>
<input type="text" class="form-control" id="name"
required
[(ngModel)]="model.name" name="name"
#name="ngModel">
<div [hidden]="name.valid || name.pristine"
class="alert alert-danger">
Please enter your name
</div>
```
5. Let's submit the form with ngSubmit directive and add type="submit" button at the bottom of the form to trigger form submit.
```html
<form (ngSubmit)="onSubmit()" #heroForm="ngForm">
// Form goes here
<button type="submit" class="btn btn-success" [disabled]="!registerForm.form.valid">Submit</button>
```
Finally, the completed template-driven registration form will be appeared as follow.
```html
<div class="container">
<h1>Registration Form</h1>
<form (ngSubmit)="onSubmit()" #registerForm="ngForm">
<div class="form-group">
<label for="name">Name</label>
<input type="text" class="form-control" id="name"
required
[(ngModel)]="model.name" name="name"
#name="ngModel">
<div [hidden]="name.valid || name.pristine"
class="alert alert-danger">
Please enter your name
</div>
</div>
<button type="submit" class="btn btn-success" [disabled]="!registerForm.form.valid">Submit</button>
</form>
</div>
```
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259. ### What are the differences between reactive forms and template driven forms?
Below are the main differences between reactive forms and template driven forms
| Feature | Reactive | Template-Driven |
|---- |---- | --------- |
| Form model setup | Created(FormControl instance) in component explicitly | Created by directives |
| Data updates | Synchronous | Asynchronous |
| Form custom validation | Defined as Functions | Defined as Directives |
| Testing | No interaction with change detection cycle | Need knowledge of the change detection process |
| Mutability | Immutable(by always returning new value for FormControl instance) | Mutable(Property always modified to new value) |
| Scalability | More scalable using low-level APIs | Less scalable using due to abstraction on APIs|
**[⬆ Back to Top](#table-of-contents)**
260. ### What are the different ways to group form controls?
Reactive forms provide two ways of grouping multiple related controls.
1. **FormGroup**: It defines a form with a fixed set of controls those can be managed together in an one object. It has same properties and methods similar to a FormControl instance.
This FormGroup can be nested to create complex forms as below.
```js
import { Component } from '@angular/core';
import { FormGroup, FormControl } from '@angular/forms';
@Component({
selector: 'user-profile',
templateUrl: './user-profile.component.html',
styleUrls: ['./user-profile.component.css']
})
export class UserProfileComponent {
userProfile = new FormGroup({
firstName: new FormControl(''),
lastName: new FormControl(''),
address: new FormGroup({
street: new FormControl(''),
city: new FormControl(''),
state: new FormControl(''),
zip: new FormControl('')
})
});
onSubmit() {
// Store this.userProfile.value in DB
}
}
```
```html
<form [formGroup]="userProfile" (ngSubmit)="onSubmit()">
<label>
First Name:
<input type="text" formControlName="firstName">
</label>
<label>
Last Name:
<input type="text" formControlName="lastName">
</label>
<div formGroupName="address">
<h3>Address</h3>
<label>
Street:
<input type="text" formControlName="street">
</label>
<label>
City:
<input type="text" formControlName="city">
</label>
<label>
State:
<input type="text" formControlName="state">
</label>
<label>
Zip Code:
<input type="text" formControlName="zip">
</label>
</div>
<button type="submit" [disabled]="!userProfile.valid">Submit</button>
</form>
```
2. **FormArray:** It defines a dynamic form in an array format, where you can add and remove controls at run time. This is useful for dynamic forms when you don’t know how many controls will be present within the group.
```js
import { Component } from '@angular/core';
import { FormArray, FormControl } from '@angular/forms';
@Component({
selector: 'order-form',
templateUrl: './order-form.component.html',
styleUrls: ['./order-form.component.css']
})
export class OrderFormComponent {
constructor () {
this.orderForm = new FormGroup({
firstName: new FormControl('John', Validators.minLength(3)),
lastName: new FormControl('Rodson'),
items: new FormArray([
new FormControl(null)
])
});
}
onSubmitForm () {
// Save the items this.orderForm.value in DB
}
onAddItem () {
this.orderForm.controls
.items.push(new FormControl(null));
}
onRemoveItem (index) {
this.orderForm.controls['items'].removeAt(index);
}
}
```
```html
<form [formControlName]="orderForm" (ngSubmit)="onSubmit()">
<label>
First Name:
<input type="text" formControlName="firstName">
</label>
<label>
Last Name:
<input type="text" formControlName="lastName">
</label>
<div>
<p>Add items</p>
<ul formArrayName="items">
<li *ngFor="let item of orderForm.controls.items.controls; let i = index">
<input type="text" formControlName="{{i}}">
<button type="button" title="Remove Item" (click)="onRemoveItem(i)">Remove</button>
</li>
</ul>
<button type="button" (click)="onAddItem">
Add an item
</button>
</div>
```
**[⬆ Back to Top](#table-of-contents)**
261. ### How do you update specific properties of a form model?
You can use `patchValue()` method to update specific properties defined in the form model. For example,you can update the name and street of certain profile on click of the update button as shown below.
```js
updateProfile() {
this.userProfile.patchValue({
firstName: 'John',
address: {
street: '98 Crescent Street'
}
});
}
```
```html
<button (click)="updateProfile()">Update Profile</button>
```
You can also use `setValue` method to update properties.
**Note:** Remember to update the properties against the exact model structure.
**[⬆ Back to Top](#table-of-contents)**
262. ### What is the purpose of FormBuilder?
FormBuilder is used as syntactic sugar for easily creating instances of a FormControl, FormGroup, or FormArray. This is helpful to reduce the amount of boilerplate needed to build complex reactive forms. It is available as an injectable helper class of the `@angular/forms` package.
For example, the user profile component creation becomes easier as shown here.
```js
export class UserProfileComponent {
profileForm = this.formBuilder.group({
firstName: [''],
lastName: [''],
address: this.formBuilder.group({
street: [''],
city: [''],
state: [''],
zip: ['']
}),
});
constructor(private formBuilder: FormBuilder) { }
}
```
**[⬆ Back to Top](#table-of-contents)**
263. ### How do you verify the model changes in forms?
You can add a getter property(let's say, diagnostic) inside component to return a JSON representation of the model during the development. This is useful to verify whether the values are really flowing from the input box to the model and vice versa or not.
```js
export class UserProfileComponent {
model = new User('John', 29, 'Writer');
// TODO: Remove after the verification
get diagnostic() { return JSON.stringify(this.model); }
}
```
and add `diagnostic` binding near the top of the form
```html
{{diagnostic}}
<div class="form-group">
// FormControls goes here
</div>
```
**[⬆ Back to Top](#table-of-contents)**
264. ### What are the state CSS classes provided by ngModel?
The ngModel directive updates the form control with special Angular CSS classes to reflect it's state. Let's find the list of classes in a tabular format,
| Form control state | If true | If false |
|---- | --------- | --- |
| Visited | ng-touched | ng-untouched |
| Value has changed | ng-dirty | ng-pristine |
| Value is valid| ng-valid | ng-invalid |
**[⬆ Back to Top](#table-of-contents)**
265. ### How do you reset the form?
In a model-driven form, you can reset the form just by calling the function `reset()` on our form model.
For example, you can reset the form model on submission as follows,
```js
onSubmit() {
if (this.myform.valid) {
console.log("Form is submitted");
// Perform business logic here
this.myform.reset();
}
}
```
Now, your form model resets the form back to its original pristine state.
**[⬆ Back to Top](#table-of-contents)**
266. ### What are the types of validator functions?
In reactive forms, the validators can be either synchronous or asynchronous functions,
1. **Sync validators:** These are the synchronous functions which take a control instance and immediately return either a set of validation errors or null. Also, these functions passed as second argument while instantiating the form control. The main use cases are simple checks like whether a field is empty, whether it exceeds a maximum length etc.
2. **Async validators:** These are the asynchronous functions which take a control instance and return a Promise or Observable that later emits a set of validation errors or null. Also, these functions passed as second argument while instantiating the form control. The main use cases are complex validations like hitting a server to check the availability of a username or email.
The representation of these validators looks like below
```js
this.myForm = formBuilder.group({
firstName: ['value'],
lastName: ['value', *Some Sync validation function*],
email: ['value', *Some validation function*, *Some asynchronous validation function*]
});
```
**[⬆ Back to Top](#table-of-contents)**
267. ### Can you give an example of built-in validators?
In reactive forms, you can use built-in validator like `required` and `minlength` on your input form controls. For example, the registration form can have these validators on name input field
```js
this.registrationForm = new FormGroup({
'name': new FormControl(this.hero.name, [
Validators.required,
Validators.minLength(4),
])
});
```
Whereas in template-driven forms, both `required` and `minlength` validators available as attributes.
**[⬆ Back to Top](#table-of-contents)**
268. ### How do you optimize the performance of async validators?
Since all validators run after every form value change, it creates a major impact on performance with async validators by hitting the external API on each keystroke. This situation can be avoided by delaying the form validity by changing the updateOn property from change (default) to submit or blur.
The usage would be different based on form types,
1. **Template-driven forms:** Set the property on `ngModelOptions` directive
```html
<input [(ngModel)]="name" [ngModelOptions]="{updateOn: 'blur'}">
```
2. **Reactive-forms:** Set the property on FormControl instance
```js
name = new FormControl('', {updateOn: 'blur'});
```
**[⬆ Back to Top](#table-of-contents)**
269. ### How to set ngFor and ngIf on the same element?
Sometimes you may need to both ngFor and ngIf on the same element but unfortunately you are going to encounter below template error.
```cmd
Template parse errors: Can't have multiple template bindings on one element.
```
In this case, You need to use either ng-container or ng-template.
Let's say if you try to loop over the items only when the items are available, the below code throws an error in the browser
```html
<ul *ngIf="items" *ngFor="let item of items">
<li></li>
</ul>
```
and it can be fixed by
```html
<ng-container *ngIf="items">
<ul *ngFor="let item of items">
<li></li>
</ul>
</ng-container>
```
**[⬆ Back to Top](#table-of-contents)**
270. ### What is host property in css?
The `:host` pseudo-class selector is used to target styles in the element that hosts the component. Since the host element is in a parent component's template, you can't reach the host element from inside the component by other means.
For example, you can create a border for parent element as below,
```js
//Other styles for app.component.css
//...
:host {
display: block;
border: 1px solid black;
padding: 20px;
}
```
**[⬆ Back to Top](#table-of-contents)**
271. ### How do you get the current route?
In Angular, there is an `url` property of router package to get the current route. You need to follow the below few steps,
1. Import Router from @angular/router
```js
import { Router } from '@angular/router';
```
2. Inject router inside constructor
```js
constructor(private router: Router ) {
}
```
3. Access url parameter
```js
console.log(this.router.url); // /routename
```
**[⬆ Back to Top](#table-of-contents)**
272. ### What is Component Test Harnesses?
A component harness is a testing API around an Angular directive or component to make tests simpler by hiding implementation details from test suites. This can be shared between unit tests, integration tests, and end-to-end tests. The idea for component harnesses comes from the **PageObject** pattern commonly used for integration testing.
**[⬆ Back to Top](#table-of-contents)**
273. ### What is the benefit of Automatic Inlining of Fonts?
During compile time, Angular CLI will download and inline the fonts that your application is using. This performance update speed up the first contentful paint(FCP) and this feature is enabled by default in apps built with version 11.
**[⬆ Back to Top](#table-of-contents)**
274. ### What is content projection?
Content projection is a pattern in which you insert, or project, the content you want to use inside another component.
**[⬆ Back to Top](#table-of-contents)**
275. ### What is ng-content and its purpose?
The ng-content is used to insert the content dynamically inside the component that helps to increase component reusability.
**[⬆ Back to Top](#table-of-contents)**
276. ### What is standalone component?
A standalone component is a type of component which is not part of any Angular module. It provides a simplified way to build Angular applications.
**[⬆ Back to Top](#table-of-contents)**
278. ### How to create a standalone component uing CLI command?
Generate standalone component using CLI command as shown below
```bash
ng generate component component-name --standalone
```
On running the command standalone component is created.
Here is the list of file created.
1. `component-name.component.ts`
2. `component-name.component.css`
3. `component-name.component.spec`
4. `component-name.component.html`
Next need to update `app.module.ts` as shown below.
```typescript
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { ComponentNameComponent } from './component-name/component-name.component';
@NgModule({
imports: [
BrowserModule,
ComponentNameComponent
],
declarations: [AppComponent],
bootstrap: [AppComponent],
})
export class AppModule {}
```
**[⬆ Back to Top](#table-of-contents)**
278. ### How to create a standalone component manually?
To make existing component to standalone, then add `standalone: true` in `component-name.component.ts`
as shown below
```typescript
import { CommonModule } from '@angular/common';
import { Component, OnInit } from '@angular/core';
@Component({
standalone: true,
imports: [CommonModule],
selector: 'app-standalone-component',
templateUrl: './standalone-component.component.html',
styleUrls: ['./standalone-component.component.css'],
})
export class ComponentNameComponent implements OnInit {
constructor() {}
ngOnInit() {}
}
```
Next need to update `app.module.ts` as shown below.
```typescript
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { ComponentNameComponent } from './component-name/component-name.component';
@NgModule({
imports: [
BrowserModule,
ComponentNameComponent
],
declarations: [AppComponent],
bootstrap: [AppComponent],
})
export class AppModule {}
```
**[⬆ Back to Top](#table-of-contents)**
278. ### What is hydration?
Hydration is the process that restores the server side rendered application on the client. This includes things like reusing the server rendered DOM structures, persisting the application state, transferring application data that was retrieved already by the server, and other processes.
To enable hydration, we have to enable server side rendering or Angular Universal. Once enabled, we can add the following piece of code in the root component.
```typescript
import {
bootstrapApplication,
provideClientHydration,
} from '@angular/platform-browser';
bootstrapApplication(RootCmp, {
providers: [provideClientHydration()]
});
```
Alternatively we can add `providers: [provideClientHydration()]` in the App Module
```typescript
import {provideClientHydration} from '@angular/platform-browser';
import {NgModule} from '@angular/core';
@NgModule({
declarations: [RootCmp],
exports: [RootCmp],
bootstrap: [RootCmp],
providers: [provideClientHydration()],
})
export class AppModule {}
```
**[⬆ Back to Top](#table-of-contents)**
| List of 300 Angular Interview Questions and answers | angular,angular-interview-questions,interview,interview-questions,javascript,javascript-interview-questions,react,typescript | 2024-03-29T05:12:41Z | 2024-03-29T05:12:33Z | null | 1 | 0 | 1 | 0 | 0 | 6 | null | null | null |
toniarndt/datalayer-helper | main | # datalayer-helper
A JavaScript library for working with datalayers.
- [Quick Start](#quick-start)
- [Latest Releases](#latest-releases)
- [Why do we need a library?](#why-do-we-need-a-library)
- [Using the library](#using-the-library)
- [Where is the data stored?](#where-is-the-data-stored)
- [Debugging](#debugging)
- [Documentation](#documentation)
- [Build and test](#build-and-test)
- [Contributing](#contributing)
- [License](#license)
## Quick Start
Download the latest version of the JS-library directly from the [dist folder](https://github.com/toniarndt/datalayer-helper/tree/main/dist) and integrate it into your website as follows.
```html
<script type="text/javascript" src="datalayer-helper.min.js"></script>
```
Alternatively, you can also integrate the source code of the library directly on the page or via a tag manager.
### Latest Releases
| Version | Description |
| ---------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------ |
| [Regular](https://raw.githubusercontent.com/toniarndt/datalayer-helper/main/dist/datalayer-helper.js) | This version is human readable, easy to edit and debug, but has a larger file size. |
| [Minified](https://raw.githubusercontent.com/toniarndt/datalayer-helper/main/dist/datalayer-helper.min.js) | This version is smaller and more difficult for humans to read, but it can be loaded more quickly by a web browser. |
## Why do we need a library?
The datalayer is an essential concept in web development, especially when working with tools like tag manager. Here are some reasons why you should use a library like this:
### Simplify data handling
The library abstracts away the complexity of dealing with the datalayer, allowing developers to focus on the logic of the application instead of managing data structures.
### Improved performance
Optimized code and reduction of redundant code in projects have a positive effect on the loading speed and execution time of scripts.
### Debugging
Integrated debugging enables simple testing of the implementation and assists with troubleshooting.
### Easier collaboration
A standardized approach to working with the datalayer simplifies teamwork by making the code easier to understand and share.
To use this library, you'll need to get it onto the page. The easiest way to do this
is by [following these instructions.](#quick-start)
## Using the library
If you are already used to working with the s-object from Adobe Analytics, using datalayer.js will feel similarly familiar to you.
We introduce a new object (**d-object**) on the page that can be accessed and that provides all the functions of the library.
Example call:
```js
d.buildDate; // to get the build date
```
## Where is the data stored?
By default, the data is saved in the global datalayer object:
```js
window._datalayer;
```
Alternatively, you can also use a custom datalayer if you already have an existing implementation.
## Debugging
Activate debugging in the library using the following code:
```js
d.setDebug(true);
```
If you set the value to 'false', you can deactivate debugging again.
A variable is created in the SessionStorage if debugging is activated. This is to allow you to concentrate on debugging.
## Documentation
For detailed documentation of the variables and functions, please use the [docs/readme.md](https://github.com/toniarndt/datalayer-helper/blob/main/docs/README.md)
## Build and test
The following are prerequisites::
- Install Node.js
- Install yarn
- Install git
Clone a copy of the project repo by running:
```
git clone https://github.com/toniarndt/datalayer-helper.git
```
Enter the datalayer.js directory and install the dependencies:
```
cd datalayer-helper
yarn install
```
You can run the linter with the command.
```
yarn lint
```
That should be everything. You can try running the build, which will compile and minify the TypeScript.
The built version (datalayer-helper.min.js) will be in the **./dist** subdirectory.
```
yarn build
```
Build:all will also build the documentation and store it in the **./docs** folder.
```
yarn build:all
```
## Contributing
If you wish to contribute to this repository, please first discuss the change you wish to make by issue, e-mail or other means with the owners of this repository before making a change. Stay friendly!
Author: [hello@toniarndt.com](mailto:hello@toniarndt.com)
## License
Copyright 2024 Toni Arndt. All rights reserved.
This work is licensed under the terms of the MIT license. For a copy, see
<https://github.com/toniarndt/datalayer-helper/blob/main/LICENSE>.
| A JavaScript library for working with datalayers. | data-layer,datalayer,javascript,typescript | 2024-04-24T19:33:35Z | 2024-05-05T19:28:36Z | null | 2 | 0 | 18 | 0 | 0 | 6 | null | MIT | TypeScript |
mudachyo/Auto-Duolingo | main | ### Languages
[](README.md) [](/translations/readme_en.md)
## Описание
Auto-Duolingo - это скрипт для автоматизации обучения на платформе Duolingo. Он помогает пользователям автоматически решать упражнения, проходить истории, зарабатывать очки опыта и поддерживать свой рейтинг в Duolingo.
 
### Режимы работы
- **Безопасный режим**: Имитирует действия пользователя, снижая риск блокировки аккаунта.
- **Турбо режим**: Увеличивает скорость авторежима, но потребляет больше ресурсов.
- **Режим пропуска уроков**: Автоматически проходит выбранное количество уроков.
- **Режим целевого опыта**: Останавливает авторежим при достижении заданного количества опыта.
### Настройки
- **Скрыть анимацию**: Отключает анимацию на сайте для повышения производительности.
- **Установить место фарма XP**: Выбирает любой урок для автоматического фарма XP.
- **Темный режим**: Включает темный режим на сайте Duolingo.
### Поставьте проекту звёздочку ⭐
Самый простой способ поддержки - поставить проекту звезду на GitHub:
## Установка
1. Установите расширение _[Violentmonkey](https://violentmonkey.github.io/get-it/)_ для вашего браузера (Chrome, Firefox, Opera, etc.)
2. Установите скрипт. _(Для автоматической установки можно перейти по [этой ссылке](https://raw.githubusercontent.com/mudachyo/Auto-Duolingo/main/Auto-Duolingo.user.js)_
3. Теперь при открытии **Duolingo** скрипт будет запускаться автоматически
## Контакты
- **[Telegram](https://t.me/mudachyo)**
- **Discord**: kotanoff
## Лицензия
- **[MIT](https://raw.githubusercontent.com/mudachyo/Auto-Duolingo/main/LICENSE/)**
| Скрипт для автоматизации обучения на Duolingo | Script for automating training on Duolingo | automation,duolingo,language-learning,userscript,xp-farming,auto,bot,solver,tampermonkey,violentmonkey | 2024-04-09T23:35:53Z | 2024-04-24T15:28:49Z | 2024-04-10T01:04:47Z | 1 | 0 | 22 | 0 | 0 | 6 | null | MIT | JavaScript |
Taverna-Hub/ForgeSheets | main | 
<p align="left">A ForgeSheets é uma aplicação web voltada para a <b>criação e gerenciamento de fichas para jogos de RPG (Role-Playing Game).</b></p>
<p align="left">Utilizando o framework <b>Django</b>, a aplicação será construída com o objetivo de oferecer à comunidade de jogadores<br>uma plataforma intuitiva e funcional para a elaboração e administração de personagens para suas aventuras.</p>
---
## 🚀 Tecnologias
<div style="display: flex; align-items: center; text-decoration: none;">
<img src="https://img.shields.io/badge/Python-7f1d1d?style=for-the-badge&logo=python&logoColor=white"/>
<img src="https://img.shields.io/badge/Django-000?style=for-the-badge&logo=django&logoColor=white"/>
<img src="https://img.shields.io/badge/sqlite-7f1d1d?style=for-the-badge&logo=sqlite&logoColor=white"/>
<img src="https://img.shields.io/badge/javascript-000?style=for-the-badge&logo=javascript&logoColor=white"/>
<img src="https://img.shields.io/badge/html5-7f1d1d?style=for-the-badge&logo=html5&logoColor=white"/>
<img src="https://img.shields.io/badge/css3-000?style=for-the-badge&logo=css3&logoColor=white"/>
<img src="https://img.shields.io/badge/Microsoft_Azure-7f1d1d?style=for-the-badge&logo=microsoft-azure&logoColor=white"/>
</div>
## 🔨 Ferramentas
<div style="display: flex; align-items: center;">
<a href="https://forgesheets.atlassian.net/jira/software/projects/SCRUM/boards/1?atlOrigin=eyJpIjoiMDJkY2ZjNTMyNDg5NGRkODlmZWQwZDc5ZTZkY2U5ZTYiLCJwIjoiaiJ9">
<img src="https://img.shields.io/badge/Jira-7f1d1d?style=for-the-badge&logo=Jira&logoColor=white"/></a>
<a href="https://www.figma.com/file/GevyRkqG9ICW9ZyhrXDtl1/Forge-Sheets-(Lo-Fi)?type=design&node-id=0%3A1&mode=design&t=1tBcAI8RKL5A3Zd2-1">
<img src="https://img.shields.io/badge/figma-000?style=for-the-badge&logo=figma&logoColor=white"/></a>
<a href="https://www.youtube.com/@Taverna-Hub">
<img src="https://img.shields.io/badge/YOUTUBE-7f1d1d?style=for-the-badge&logo=youtube&logoColor=white"/></a>
<img src="https://img.shields.io/badge/discord-000?style=for-the-badge&logo=discord&logoColor=white"/>
</div>
<br/>
<br/>
# Entrega 01
<br/>
<p align="center" style="">
<a href="https://www.youtube.com/watch?v=oNvP1qluKYE"">
<img src="https://img.shields.io/badge/screencast-7f1d1d?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://www.figma.com/file/GevyRkqG9ICW9ZyhrXDtl1/Forge-Sheets-(Lo-Fi)?type=design&node-id=0%3A1&mode=design&t=1tBcAI8RKL5A3Zd2-1">
<img src="https://img.shields.io/badge/figma-000?style=for-the-badge&logo=figma&logoColor=white" height="35px"/></a>
<a href="https://forgesheets.atlassian.net/jira/software/projects/SCRUM/boards/1?atlOrigin=eyJpIjoiMDJkY2ZjNTMyNDg5NGRkODlmZWQwZDc5ZTZkY2U5ZTYiLCJwIjoiaiJ9">
<img src="https://img.shields.io/badge/jira-7f1d1d?style=for-the-badge&logo=Jira&logoColor=white" height="35px"/></a>
</p>
<br/>
- <strong> Backlog </strong>
<br/>
- <strong> Board </strong>
---
# Entrega 02
<br/>
<p align="center" style="">
<a href="https://youtu.be/ICCpQ_v98Ag?si=JbpMcWvCwF-y9nmI"">
<img src="https://img.shields.io/badge/screencast-7f1d1d?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://docs.google.com/document/d/13SVAn4s2bloI9BRC-cFVQm3AeOYhq9guzU9kyz2zRFk/edit?usp=sharing"">
<img src="https://img.shields.io/badge/relatório programação em par-000000?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://forgesheets.azurewebsites.net/"">
<img src="https://img.shields.io/badge/site na azure-7f1d1d?style=for-the-badge&logo=microsoft-azure&logoColor=white" height="35px"/></a>
</p>
<br/>
- <strong> Instruções de acesso </strong>
<p align="center" style="">
<a href="https://scribehow.com/shared/Cadastro_e_Login_no_ForgeSheets___UA3MjHAQj6dw8Te9NOScw?referrer=documents"">
<img src="https://img.shields.io/badge/Cadastro / Login-7f1d1d?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://scribehow.com/shared/Como_criar_sua_ficha_corretamente_no_ForgeSheets__AP6rEuLqThmEmttf2IWEHA?referrer=documents"">
<img src="https://img.shields.io/badge/Criação de Ficha-000000?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://scribehow.com/shared/Criando_uma_campanha_no_Forgesheets__Zvl76TYgTZOOdZd_tJr-tg?referrer=documents"">
<img src="https://img.shields.io/badge/Criação de Campanha-7f1d1d?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://scribehow.com/shared/Como_gerenciar_seus_equipamentos_no_ForgeSheets__EiE0ewe9S0eX6An4SjFzdA?referrer=documents"">
<img src="https://img.shields.io/badge/Gerenciamento de Equipamentos-000?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
</p>
<br/>
- <strong> Backlog </strong>
<br/>
- <strong> Board </strong>
- <strong> Issues </strong>
- <strong> Diagrama de Atividades </strong>
---
# Entrega 03
<p align="center" style="">
<a href="https://www.youtube.com/watch?v=uObGl7P5vn8">
<img src="https://img.shields.io/badge/screencast das histórias em produção-7f1d1d?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://youtu.be/ZCStFsnDZT8?si=73OPqXMBNbqnK4zG">
<img src="https://img.shields.io/badge/screencast dos protótipos-000000?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://youtu.be/VOIWmgm4sTY">
<img src="https://img.shields.io/badge/screencast de build & deploy-7f1d1d?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://youtu.be/kco5XmxPI1Y">
<img src="https://img.shields.io/badge/screencast dos testes e2e-000000?style=for-the-badge&logo=youtube&logoColor=white" height="35px"/></a>
<a href="https://docs.google.com/document/d/13SVAn4s2bloI9BRC-cFVQm3AeOYhq9guzU9kyz2zRFk/edit?usp=sharing"">
<img src="https://img.shields.io/badge/relatório programação em par-7f1d1d?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://forgesheets.azurewebsites.net/"">
<img src="https://img.shields.io/badge/site na azure-000000?style=for-the-badge&logo=microsoft-azure&logoColor=white" height="35px"/></a>
</p>
<br/>
- <strong> Instruções de acesso </strong>
<p align="center" style="">
<a href="https://scribehow.com/shared/Como_visualizar_e_editar_os_atributos_do_seu_personagem_no_ForgeSheets__6_HKY66rRPyqp766QfkfNA?referrer=documents"">
<img src="https://img.shields.io/badge/Gerenciamento de Fichas-000000?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://scribehow.com/shared/Como_visualizar_e_editar_as_magias_do_seu_personagem_no_ForgeSheets__nzhMsENFSKmYa9inqnzpew?referrer=documents"">
<img src="https://img.shields.io/badge/Gerenciamento de Magias na Ficha-7f1d1d?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
<a href="https://scribehow.com/shared/Como_executar_uma_Rolagem_de_Dados_no_ForgeSheets__AJSbfUhySpWku3OfWnAx2g?referrer=documents"">
<img src="https://img.shields.io/badge/Rolagem de Dados-000000?style=for-the-badge&logo=googledocs&logoColor=white" height="35px"/></a>
</p>
<br/>
- <strong> Backlog </strong>
<br/>
- <strong> Board </strong>
<br/>
- <strong> Issues </strong>
<br/>
- <strong> Diagrama de Atividades Atualizado </strong>
---
## 👥 Equipe
<table>
<tr>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/Pandor4b">
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;"
>
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/1f1b6267-1c09-4a45-9f8d-962091d19469" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Ana Clara"/>
</div>
<br />
<sub style="font-size:14px"><b>Ana Clara</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/deadcube04" >
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;"
>
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/70b42b25-007f-439e-ae79-ff9b0b93cd0f" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px;" alt="Gabriel"/>
</div>
<br />
<sub style="font-size:14px"><b>Gabriel</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/gustavoyoq">
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;"
>
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/9e28af63-09ca-43ac-ba4e-e3a44bdad3db" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Gustavo"/>
</div>
<br />
<sub style="font-size:14px"><b>Gustavo</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href=https://github.com/n3waz>
<div style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;">
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/7fc1f353-1103-4a0b-becb-c60cc05b69b1" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Luan"/>
</div>
<br />
<sub style="font-size:14px;"><b>Luan</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/paulorosadodev">
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;">
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/87e696b5-7b42-4d03-aa4f-775800e990cf" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Paulo"/>
</div>
<br />
<sub style="font-size:14px"><b>Paulo</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/sophia-15">
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;"
>
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/fd713c44-4d59-4156-9b5d-5ab73abd9df6" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Sophia">
</div>
<br />
<sub style="font-size:14px"><b>Sophia</b></sub>
</a>
</td>
<td align="center" style="word-wrap: break-word; width: 150.0; height: 150.0">
<a href="https://github.com/viniciusdandrade">
<div
style="border: 3px solid #7f1d1d; border-radius: 50%; width: 115px; height: 115px; display: flex; align-items: center; justify-content: center;">
<img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/e0561385-0849-4a2a-a8e4-ed90baf3ee8d" style="border-radius:50%;align-items:center;justify-content:center;overflow:hidden; width: 150px; " alt="Vinícius"/>
</div>
<br />
<sub style="font-size:14px"><b>Vinícius</b></sub>
</a>
</td>
</tr>
</table>
---
<p align="center">
<a href="https://github.com/Taverna-Hub">
<img src="data:image/svg+xml;base64,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"/>
</a>
</p>
<p align="center"><img src="https://github.com/Taverna-Hub/ForgeSheets/assets/117609505/9287638f-8716-4e62-9989-a40882fbfed6" width="40px"></p>
<p align="center">Projeto para a disciplina de <strong>Fundamentos de Desenvolvimento de Software</strong> na <strong>CESAR School</strong></p>
| Uma aplicação web de criação e gerenciamento de fichas para RPG utilizando Django. | azure,cesar-school,css,django,html,javascript,python,rpg,sqlite,cypress | 2024-03-17T16:20:20Z | 2024-05-20T23:18:46Z | null | 7 | 33 | 551 | 4 | 0 | 6 | null | MIT | CSS |
gutenye/ocr | main | # Guten OCR
> [Demo](https://gutenye-ocr.netlify.app/) | [Roadmap](https://github.com/users/gutenye/projects/5/views/4)
**an OCR Javascript library runs on Node.js, Browser, React Native and C++**
Based on [PaddleOCR](https://github.com/PaddlePaddle/PaddleOCR) and [ONNX Runtime](https://github.com/microsoft/onnxruntime), supports PP-OCRv4 model
## Getting Started
### Node
> [Example](./packages/node/example/README.md)
```ts
bun add @gutenye/ocr-node
import Ocr from '@gutenye/ocr-node'
const ocr = await Ocr.create()
const result = await ocr.detect('a.jpg')
```
### Browser
> [Example](./packages/browser/example/README.md)
```ts
bun add @gutenye/ocr-browser
import Ocr from '@gutenye/ocr-browser'
const ocr = await Ocr.create({
models: {
detectionPath: '/assets/ch_PP-OCRv4_det_infer.onnx',
recognitionPath: '/assets/ch_PP-OCRv4_rec_infer.onnx',
dictionaryPath: '/assets/ppocr_keys_v1.txt'
}
})
const result = await ocr.detect('/a.jpg')
```
### React Native
> [Example](./packages/react-native/example/README.md)
```ts
bun add @gutenye/ocr-react-native
import Ocr from '@guenye/ocr-react-native'
const ocr = await Ocr.create()
const result = await ocr.detect('a.jpg')
```
### C++
> [Example](./packages/react-native/cpp/example/README.md)
```cpp
#include "native-ocr.h"
NativeOcr* ocr = new NativeOcr(..)
auto result = ocr->detect("a.jpg");
```
### API Reference
```ts
Ocr.create({
models?: {
detectionPath: string
recognitionPath: string
dictionaryPath: string
},
isDebug?: boolean
debugOutputDir?: string // Node only
recognitionImageMaxSize?: number // RN only
detectionThreshold?: number // RN only
detectionBoxThreshold?: number // RN only
detectionUnclipRatiop?: number // RN only
detectionUseDilate?: boolean // RN only
detectionUsePolygonScore?: boolean // RN only
useDirectionClassify?: boolean // RN only
onnxOptions?: {} // Node only. Pass to ONNX Runtime
}): Promise<Ocr>
ocr.detect(imagePath, {
onnxOptions?: {} // Node only. Pass to ONNX Runtime
}): Promise<Result>
```
## Development
- Requires Git LFS to clone the repo
```sh
brew install git-lfs
git clone git@github.com:gutenye/ocr.git
```
- [Development](docs/Development.md)
## Related Projects
| Name | Platforms | Note |
| -------------------------------------------------------------- | --------- | ------------------------------- |
| [eSearch-OCR](https://github.com/xushengfeng/eSearch-OCR) | Electron | |
| [paddleocr-onnx](https://github.com/backrunner/paddleocr-onnx) | Node | Recogination part is incomplete |
| [ocrjs](https://github.com/SOVLOOKUP/ocrjs) | Node | Recogination part is incomplete |
| [Paddle-Lite-Demo](https://github.com/PaddlePaddle/Paddle-Lite-Demo) | Mobile, C++ | |
| High accurate text detection (OCR) Javascript/Typescript library that runs on Node.js, Browser, React Native and C++. Based on PaddleOCR and ONNX runtime | browser,javascript,node,ocr,onnxruntime,paddleocr,react-native,text-detection,typescript,cpp | 2024-05-01T08:03:27Z | 2024-05-20T16:40:58Z | null | 2 | 1 | 197 | 0 | 1 | 6 | null | MIT | C++ |
leoforney/accel_sort | master | # accel-sort
[](https://badge.fury.io/js/accel-sort)
A high performance sorting library for Javascript. Get up to **70x** speedup when sorting ints and floats
## Prerequisites
- NVIDIA GPU with CUDA Compute Capability (5.0 or higher)
- Node.js (Version 12.x or higher)
- CUDA Version 12.4 installed
## Installation
Run `npm install accel-sort`
## Building from source
Make sure you have `nvcc` installed on your system, then simply run
```shell
npm install
```
## Usage
Simply import the `AccelSort` with the following:
```javascript
const AccelSort = require("accel-sort");
```
Within AccelSort, pass it the specified array types and size to their dedicated functions:
### sortIntegers:
```javascript
let array = new Int32Array([3, 1, 2]);
let buffer = Buffer.from(array.buffer);
AccelSort.sortIntegers(buffer, array.length);
```
### sortFloat:
```javascript
let array = new Float32Array([5.8, -10.7, 1507.6563, 1.0001]);
let buffer = Buffer.from(array.buffer);
AccelSort.sortFloats(buffer, array.length);
```
After that, the original `array` object will be correctly sorted in place
## Contributions
Contributions are welcome! Please submit a pull request or open an issue to discuss proposed changes or additions.
## License
Distributed under the MIT License. See LICENSE for more information. | High performance sorting library for javascript | cuda,javascript,sorting,thrust | 2024-03-26T00:18:05Z | 2024-04-01T16:37:29Z | null | 1 | 0 | 7 | 6 | 0 | 6 | null | MIT | JavaScript |
RS-labhub/I-Love-You | main | null | Is your crush constantly denying your love? No worries, just send this to her! | bootstrap5,css3,flagsmith,html5,javascript | 2024-04-03T15:50:20Z | 2024-04-06T14:50:58Z | null | 1 | 0 | 70 | 0 | 0 | 6 | null | Apache-2.0 | JavaScript |
titanilham/ToDoList | main | <img src="https://readme-typing-svg.demolab.com?font=Electrolize&size=25&pause=1000&color=11EAF7&random=false&width=435&lines=ToDoList" alt="Typing SVG" />
### Languages:
* JavaScript <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/JavaScript-logo.png/120px-JavaScript-logo.png" width="15" height="15"/>
* Html <img src="https://raw.githubusercontent.com/devicons/devicon/1119b9f84c0290e0f0b38982099a2bd027a48bf1/icons/html5/html5-original.svg" width="15" height="15"/>
* Css <img src="https://raw.githubusercontent.com/devicons/devicon/1119b9f84c0290e0f0b38982099a2bd027a48bf1/icons/css3/css3-original.svg" width="15" height="15"/>
### Preview:
<a href="https://to-dol1st.netlify.app/">Link to the site</a>
### Password and user name in config.json
----
<div id="badges">
<a href="https://vk.com/aniime_guy" >
<img src="https://img.icons8.com/?size=512&id=13977&format=png"width="40" height="40" title="VK"/>
</a>
<a href="https://t.me/Ilham06">
<img src="https://img.icons8.com/?size=512&id=63306&format=png"width="40" height="40" title="Telegram"/>
</a>
<a href="https://www.youtube.com/channel/UC9m1N5x0OXWihGpR50Yk35g">
<img src="https://github.com/titanilham/titanilham/assets/86422270/51f7c427-b7b3-4591-9243-2f2c3465d742" width="40" height="40" title="YouTube"/>
</a>
<a href="https://discord.com/channels/1019531122239094794/1019531122239094801">
<img src="https://www.freepnglogos.com/uploads/discord-logo-png/discord-logo-logodownload-download-logotipos-1.png" width="40" height="40" title="Discord"/>
</a>
</div>
| My site | archive,css,html,javascript,notes,sign-in,site,to-do-list,web,website | 2024-03-16T10:00:33Z | 2024-05-15T14:23:19Z | 2024-03-16T10:31:15Z | 1 | 0 | 19 | 1 | 0 | 6 | null | AGPL-3.0 | CSS |
davevad93/rest-countries-django-app | main | # Rest Countries Info APP [](https://opensource.org/licenses/MIT)  
## - Introduction -
**Rest Countries Info APP** is a small Django project that utilizes the [REST Countries API](https://restcountries.com/) and the [Wikipedia API](https://www.mediawiki.org/wiki/API:Main_page) to provide specific information about countries around the world. The project is built using Python 3.12, JavaScript, Bootstrap 5, HTML5, CSS3, and JSON. This is the first project I ever released on GitHub and my first Django project overall so there may be errors, therefore any contribution or advice is welcome.
## - Requirements -
Make sure you have Python installed on your system, you can check this by running on the command line:
```bash
py --version # Windows
python --version # Unix/macOS
```
If you don't have Python installed go to https://www.python.org/downloads/ and download the latest version.
## - Installation -
1. Clone the repository:
```bash
git clone https://github.com/davevad93/rest-countries-django-app.git
```
2. Go to the repo directory:
```bash
cd rest-countries-django-app
```
3. Create a virtual environment:
```bash
py -m venv venv # Windows
python -m venv venv # Unix/macOS
```
4. Activate the virtual environment:
```bash
venv/Scripts/activate.bat # Windows
source venv/bin/activate # Unix/macOS
```
5. Go to the project directory:
```bash
cd myproject
```
6. Install the required dependencies:
```bash
py -m pip install -r requirements.txt # Windows
python -m pip install -r requirements.txt # Unix/macOS
```
7. Generate a random Secret Key and store it inside the .env file: <br/>
(This app doesn't utilize an authentication system and doesn't store any sensitive data, however it is always a good habit to generate a Secret Key and store it in your enviroment file).
```bash
# STEP 1: Open the Python Shell within the terminal.
py manage.py shell # Windows
python manage.py shell # Unix/macOS
```
```bash
# STEP 2: Import the get_random_secret_key() function.
from django.core.management.utils import get_random_secret_key
```
```bash
# STEP 3: Generate the Secret Key using the get_random_secret_key() function.
print(get_random_secret_key())
# Copy the key.
```
```bash
# STEP 4: Exit the Python Shell.
exit()
```
```bash
# STEP 5: Create .env file with the "SECRET_KEY" environment variable and paste the generated key in STEP 3.
echo SECRET_KEY = 'Paste here the key generated in STEP 3' > .env
```
8. Run the development server:
```bash
py manage.py runserver # Windows
python manage.py runserver # Unix/macOS
```
9. Access the application in your web browser at `http://localhost:8000`.
## - Features -
- ### Search for countries by name.
- ### Filter for countries by region.
- ### View detailed information about each country.
- ### Search feature by clicking on the cards.
## - Notes -
There may be some inconsistencies about the information of certain countries. This is due to the fact that to display the basic information of each country (e.g. population) I've used the **REST Countries API** (last updated in 2021) while to display countries descriptions I've used the **Wikipedia API** (which is constantly updated). To give an example, in the REST countries data, the most populated country in the world is China, but In 2022 India overtook it as the world's country with the largest population.
## - Made with -
- [](https://www.python.org)
- [](https://www.djangoproject.com)
- [](https://www.javascript.com)
- [](https://getbootstrap.com)
- [](https://html.com)
- [](https://css3.com)
## - Acknowledgments -
- [REST Countries API](https://restcountries.com/) for the general **country data** showed in the app.
- [Wikipedia API](https://www.mediawiki.org/wiki/) for the **country descriptions** displayed in the app.
- [Font Awesome](https://fontawesome.com/) for the **fa-search** icon used in the app search bar.
- [Awesome Badges](https://github.com/Envoy-VC/awesome-badges) for the badges used in the "**Made with**" section.
## - Credits -
A few country emblems displayed in this project aren't from the [REST Countries API JSON](https://restcountries.com/v3.1/all) because some key values are null, so I have fetched the missing ones from [Wikimedia Commons](https://commons.wikimedia.org/wiki/Main_Page). Most of them are in the public domain and don't need attribution but some are under Creative Commons licenses hence, I'm going to give the due credit to the authors.
- [Demidow](https://commons.wikimedia.org/wiki/User:Demidow), [Coat of arms of the British Indian Ocean Territory](https://commons.wikimedia.org/wiki/File:Coat_of_arms_of_the_British_Indian_Ocean_Territory.svg), [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/legalcode)
- [Spedona](https://commons.wikimedia.org/wiki/User:Spedona), [Clunies-Ross family arms](https://commons.wikimedia.org/wiki/File:Clunies-Ross_family_arms.svg), [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/legalcode)
- [Squiresy92](https://commons.wikimedia.org/wiki/User:Squiresy92) & [Sodacan](https://commons.wikimedia.org/wiki/User:Sodacan), [Coat of arms of Norfolk Island](https://commons.wikimedia.org/wiki/File:Coat_of_arms_of_Norfolk_Island.svg), [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/legalcode)
- [Heralder](https://commons.wikimedia.org/wiki/User:Heralder), [Coat of arms of the Commonwealth of Puerto Rico](https://commons.wikimedia.org/wiki/File:Coat_of_arms_of_the_Commonwealth_of_Puerto_Rico.svg), [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/legalcode)
- [Superbenjamin](https://commons.wikimedia.org/wiki/User:Superbenjamin), [Armoiries Réunion](https://commons.wikimedia.org/wiki/File:Armoiries_R%C3%A9union.svg), [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/legalcode)
- [Manassas](https://commons.wikimedia.org/wiki/User_talk:Manassas~commonswiki), [Blason St Barthélémy TOM entire](https://commons.wikimedia.org/wiki/File:Blason_St_Barth%C3%A9l%C3%A9my_TOM_entire.svg), [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/legalcode)
- [Di (they-them)](https://commons.wikimedia.org/wiki/User:Di_(they-them)), [Coat of Arms of Saint Helena](https://commons.wikimedia.org/wiki/File:Coat_of_Arms_of_Saint_Helena.svg), [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/legalcode)
- [Government of the Collectivity of Saint-Martin](https://www.com-saint-martin.fr), [Local flag of the Collectivity of Saint Martin](https://commons.wikimedia.org/wiki/File:Local_flag_of_the_Collectivity_of_Saint_Martin.svg), [Licence Ouverte 2.0](https://www.etalab.gouv.fr/wp-content/uploads/2018/11/open-licence.pdf)
- [Josedar](https://commons.wikimedia.org/wiki/User:Josedar), [Coat of arms of the Turks and Caicos Islands](https://commons.wikimedia.org/wiki/File:Coat_of_arms_of_the_Turks_and_Caicos_Islands.svg), [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/legalcode)
## - Contributing -
Contributions are truly welcome! If you find any issues or have suggestions for improvements, please open an issue or fork the repository and submit a pull request. Don't forget to give this project a star. Thank you very much!
## - License -
This project is licensed under the MIT License. See the [LICENSE](LICENSE) file for more information.
| Small project built with Django that retrieves data from the REST Countries API and the Wikipedia API. | alicante,bootstrap,css,django,espanol,html,italiano,javascript,python,rest-countries-api | 2024-03-23T20:01:24Z | 2024-04-28T21:06:55Z | null | 2 | 20 | 86 | 0 | 0 | 6 | null | MIT | CSS |
piyush-eon/currency-converter | master | # Build a Currency Converter with React JS and Tailwind CSS
## [Click Here to Watch Full tutorial on Youtube](https://www.youtube.com/watch?v=Y1Q4XXXmVk4)
| Build a Currency Converter with React JS and Tailwind CSS | javascript,react,tailwindcss | 2024-03-30T15:57:21Z | 2024-04-01T04:20:10Z | null | 1 | 0 | 2 | 0 | 2 | 6 | null | null | JavaScript |
PrabothCharith/accessibility-plugin | main | # Accessibility Plugin
[](https://badge.fury.io/js/accessibility-plugin)
## Description
The Accessibility Plugin is a JavaScript library that helps improve the accessibility of your web applications. It provides a set of utility functions and components that can be easily integrated into your project.
## Features
- **Invert Colors**: Inverts the colors of the page to improve readability for users with visual impairments.
- **Grayscale**: Converts the page grayscale to improve readability for users with visual impairments.
- **Low Saturation**: Reduces the saturation of the page to improve readability for users with visual impairments.
- **High Saturation**: Increases the saturation of the page to improve readability for users with visual impairments.
- **Link Highlight**: Highlights all links on the page to make them easier to identify for users with visual impairments.
- **Font Size**: Increases the font size of the page to improve readability for users with visual impairments.
- **Line Height**: Increases the line height of the page to improve readability for users with visual impairments.
- **Letter Spacing**: Increases the letter spacing of the page to improve readability for users with visual impairments.
- **Text Alignment**: Changes the text alignment of the page to improve readability for users with visual impairments.
- **Low Contrast**: Reduces the contrast of the page to improve readability for users with visual impairments.
- **High Contrast**: Increases the contrast of the page to improve readability for users with visual impairments.
- **Extra Contrast**: Increases the contrast of the page even further to improve readability for users with visual impairments.
- **Hide Images**: Hides all images on the page to improve readability for users with visual impairments.
- **Hide Videos**: Hides all videos on the page to improve readability for users with visual impairments.
- **Big Circle Cursor**: Changes the cursor to a big circle to improve visibility for users with visual impairments.
- **Reading Mask**: Highlights the current line of text being read to improve focus for users with visual impairments.
- **Reading Guide**: Makes it easier to read long lines of text by Long Highlight Cursor.
- **Reset**: Resets all accessibility settings to their default values.
- **Close**: Closes the accessibility menu.
- **Change Position**: You can change the position of the accessibility menu to `left`, `right`, `top` or `bottom` as User needs.
- **Save Settings**: Save the current settings to the local storage and load them when the page is reloaded.
## Installation
You can install the Accessibility Plugin using npm. Run the following command in your project directory:
<pre><code>npm i accessibility-plugin</code></pre>
### OR
You can use this `CDN` easily.
<pre><code>https://cdn.jsdelivr.net/gh/PrabothCharith/accessibility-plugin@main/accessibility-menu.min.js</code></pre>
<pre><code><script src="https://cdn.jsdelivr.net/gh/PrabothCharith/accessibility-plugin@main/accessibility-menu.min.js"></script></code></pre>
<br/>
After installation, you can link the `javascript` file _normally_ using
<pre><code><script src="node_modules/accessibility-plugin/accessibility-menu.js"></script></code></pre>
### OR
You can use `min.js` file _as your requirement_
<pre><code><script src="node_modules/accessibility-plugin/accessibility-menu.min.js"></script></code></pre>
>[!tip]
> **Link the `Javascript` file `after all javascript` for better output**
## Customization
### Change Position
- In the js file, you can find the `first div` with `id` as `accessibility-modal`
- In this div, you can find class `right` by **default**. You can change it to `left`, `right`, `top` or `bottom` as you need
## Preview
<video style='width:100%; height:auto;' src='https://github.com/PrabothCharith/accessibility-plugin/assets/91902549/e310ea92-e434-4c35-a2d5-f1c99547e98e'></video>
| The Accessibility Plugin is a JavaScript library that helps improve the accessibility of your web applications. It provides a set of utility functions and components that can be easily integrated into your project. | accessibility,accessibility-plugin,accessibility-service,accessibility-toolbar,accessibility-tools,accessibilityservice,free-accessibility,free-plugin,javascript,javascript-library | 2024-04-19T10:02:25Z | 2024-05-09T07:34:58Z | 2024-05-06T04:37:23Z | 3 | 19 | 142 | 0 | 5 | 6 | null | GPL-3.0 | JavaScript |
flurryunicorn/AppStack-React | main | # AppStack: Fully-featured Dashboard Template based on React & Bootstrap
## Documentation
### Introduction
Hello, hope you find this template useful. AppStack React has been crafted on top of Bootstrap 5 and React. It's documentation does not replace the official Bootstrap 5 documentation but rather supplements it by providing a comprehensive view of all extended styles and new components that this template provides on top of Bootstrap 5. It covers various aspects like incoming about the template organization, necessary changes in the source code, and how to compile and extend it the way you want.
## Table of Contents
- Getting started
- Environment Variables
- Routing
- Auth0 Authentication
- Firebase Authentication
- JWT Authentication
- Guards
- Deployment
- API Calls
- Redux
- Internationalization
- ESLint & Prettier
- Migrating to Next.js
---
## Getting Started
### Installation
This repo is using Vite so please install Node.js before using Appstack React.
### Clone the Repository
As a first step, you need to clone the repository to your local machine. You can do this with the following command:
```bash
git clone https://github.com/flurryunicorn/AppStack-React
```
After Node.js is installed, run `npm install` to get all the dependencies of Appstack React. All of them will be downloaded to the node_modules directory.
```bash
npm install
```
Once ready, you can start modifying source files and see changes at http://localhost:3000. AppStack uses webpack and webpack-serve to automatically detect file changes and start a local webserver.
```bash
npm start
```
### Build tools
Starting a local webserver at http://localhost:3000 and autodetect file changes:
```bash
npm start
```
To compile, optimize, minify and uglify all source files into the `build/` directory:
```bash
npm run build
```
### Contents
Once you have cloned the project, you will find directories and files as listed below. The package includes both the compiled and minified 'distribution' files, as well as the source files.
```markdown
theme/
├── .eslintrc
├── .gitignore
├── .prettierrc
├── package.json
├── package-lock.json
├── README.md
├── build/
├── public/
│ ├── favicon.ico
│ └── index.html
└── src/
├── assets/
│ ├── img/
│ └── scss/
├── components/
├── contexts/
├── helpers/
├── hooks/
├── layouts/
├── pages/
├── App.js
├── constants.js
├── routes.js
└── index.js
```
## Environment Variables
### Introduction
Your project can consume variables declared in your environment as if they were declared locally in your JS files. By default, you will have `NODE_ENV` defined for you, and any other environment variables starting with `VITE_`.
### Adding Environment Variables
To define permanent environment variables, create a file called `.env` in the root of your project:
```bash
VITE_NOT_SECRET_CODE=abcdef
```
**Note:** You need to restart the development server after changing `.env` files.
### Accessing Environment Variables
Environment variables will be defined for you on `process.env`. For example, having an environment variable named `VITE_NOT_SECRET_CODE` will be exposed in your JS as `process.env.VITE_NOT_SECRET_CODE`.
```javascript
if (process.env.NODE_ENV !== 'production') {
// do something
}
```
```jsx
<title>{process.env.VITE_WEBSITE_NAME}</title>
```
**Note:** You need to restart the development server after changing `.env` files.
### Learn More
To learn more about environment variables, click [here](<https://vitejs.dev/guide/env-and-mode.html>).
## Routing
### Introduction
The package includes an implementation of React Router DOM, using the programmatic routing model.
### How to Add Routes
To add a new route, open `/src/routes.js` and add your new route to the `routes` variable. The example below will create a route `http://localhost:3000/pages/new` that renders the `<NewPage />` component:
```javascript
import DashboardLayout from "./layouts/Dashboard";
import NewPage from "./pages/NewPage";
const routes = [
{
path: "pages",
element: <DashboardLayout />,
children: [
{
path: "new",
element: <NewPage />,
},
],
},
];
export default routes;
```
### How to Add a Link
Follow these steps to add a link to a component:
```jsx
import { Link } from "react-router-dom";
function ExampleComponent() {
return (
<Link to="pages/new">
New page
</Link>
);
}
export default ExampleComponent;
```
### How to Navigate Programmatically
Below is the example showing how you can navigate programmatically using the `useNavigate` hook:
```jsx
import { useNavigate } from "react-router-dom";
function ExampleComponent() {
const navigate = useNavigate();
const handleSubmit = () => {
navigate("/pages/new");
};
return (
<form onSubmit={handleSubmit}>
...
</form>
);
}
export default ExampleComponent;
```
## Auth0
### Introduction
Auth0 is an easy to implement, adaptable authentication and authorization platform. It allows you to rapidly integrate authentication and authorization for web, mobile, and legacy applications so you can focus on your core business.
### Quick Start
Follow these steps if you want to enable Auth0 authentication in your application.
1. **Enable AuthProvider**
Enable Auth0's `AuthProvider` in `/src/App.js`.
```jsx
import { AuthProvider } from "./contexts/Auth0Context";
function App() {
return (
<AuthProvider>
{content}
</AuthProvider>
)
}
```
2. **Enable useAuth hook**
Enable Auth0's `useAuth` hook in `/src/hooks/useAuth.js`.
```jsx
import { AuthContext } from "../contexts/Auth0Context";
const useAuth = () => {
return useContext(AuthContext);
};
```
### How to Use
Learn how to use Auth0 authentication. There are multiple examples included, including sign in, sign up and sign out.
To retrieve user info:
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { displayName } = useAuth();
return (
<span>
{user.displayName}
</span>
);
};
```
To execute actions (like sign in):
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { signIn } = useAuth();
return (
<button onClick={() => signIn()}>
Sign in
</button>
);
};
```
## Firebase
### Introduction
Firebase Authentication provides backend services, easy-to-use SDKs, and ready-made UI libraries to authenticate users to your app. It supports authentication using passwords, phone numbers, popular federated identity providers like Google, Facebook and Twitter, and more.
### Quick Start
Here are steps to enable Firebase authentication in your application.
1. **Enable AuthProvider**
Enable Firebase's `AuthProvider` in `/src/App.js`.
```jsx
import { AuthProvider } from "./contexts/FirebaseContext";
function App() {
return (
<AuthProvider>
{content}
</AuthProvider>
)
}
```
2. **Enable useAuth hook**
Enable Firebase's `useAuth` hook in `/src/hooks/useAuth.js`.
```jsx
import { AuthContext } from "../contexts/FirebaseContext";
const useAuth = () => {
return useContext(AuthContext);
};
```
### How to Use
Learn how to use Firebase authentication. Examples included below cover operations such as sign in, sign up and sign out.
To retrieve user info:
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { displayName } = useAuth();
return (
<span>
{user.displayName}
</span>
);
};
```
To execute sign in actions:
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { signIn, signInWithGoogle } = useAuth();
return (
<React.Fragment>
<button onClick={() => signIn()}>
Regular Sign in
</button>
<button onClick={() => signInWithGoogle()}>
Sign in with Google
</button>
</React.Fragment>
);
};
```
## JSON Web Token (JWT)
### Introduction
JSON Web Token (JWT) is an open standard that defines a compact and self-contained way for securely transmitting information between parties as a JSON object.
### Quick Start
If you want to enable JWT authentication in your application, below are the steps:
1. **Enable AuthProvider**
Enable JWT's `AuthProvider` in `/src/App.js`.
```jsx
import { AuthProvider } from "./contexts/JWTContext";
function App() {
return (
<AuthProvider>
{content}
</AuthProvider>
)
}
```
2. **Enable useAuth hook**
Enable JWT's `useAuth` hook in `/src/hooks/useAuth.js`.
```jsx
import { AuthContext } from "../contexts/JWTContext";
const useAuth = () => {
return useContext(AuthContext);
};
```
### How to Use
Learn how to use JWT authentication. Here are examples for operations such as sign in, sign up and sign out.
To retrieve user info:
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { displayName } = useAuth();
return (
<span>
{user.displayName}
</span>
);
};
```
To execute actions (like sign in):
```jsx
import useAuth from '../hooks/useAuth';
const App = () => {
const { signIn } = useAuth();
return (
<button onClick={() => signIn()}>
Sign in
</button>
);
};
```
## Guards
### Introduction
Guards can be used to protect certain routes based on the role of current user.
### Auth Guard
The `AuthGuard` component can be used to prevent unauthenticated users from accessing private routes.
```jsx
import AuthGuard from "../components/guards/AuthGuard";
function Component() {
return (
<AuthGuard>
<PrivateExampleComponent />
</AuthGuard>
)
}
```
### Guest Guard
The `GuestGuard` component can be used to prevent authenticated users from accessing certain routes.
```jsx
import GuestGuard from "../components/guards/GuestGuard";
function Component() {
return (
<GuestGuard>
<PublicExampleComponent />
</GuestGuard>
)
}
```
## Deployment
### Introduction
The command `npm run build` creates a `build` directory with a production build of your app. You should set up your preferred HTTP server, so that a visitor to your site is served `index.html`, and requests to static paths such as `/static/js/main.<hash>.js` are served with the contents of the `/static/js/main.<hash>.js` file.
### Static Server
For Node environments, the easiest way to handle this is installing `serve`:
```bash
npm install -g serve
serve -s build
```
The last command will serve your static site on port `5000`. You can adjust the port using the `-l` or `--listen` flags:
```bash
serve -s build -l 4000
```
To get a full list of available options:
```bash
serve -h
```
### Other Solutions
You don’t necessarily need a static server to run a Create React App project in production. It works well when integrated into an existing server-side app.
### Express
Express is a fast, unopinionated, minimalist web framework for Node.js. See the programmatic example:
```javascript
const express = require('express');
const path = require('path');
const app = express();
app.use(express.static(path.join(__dirname, 'build')));
app.get('/', function(req, res) {
res.sendFile(path.join(__dirname, 'build', 'index.html'));
});
app.listen(9000);
```
### Netlify
Netlify deploys modern static websites. With Netlify, you gain access to a CDN, continuous deployment, one-click HTTPS, and more services.
To manually deploy to Netlify’s CDN:
```bash
npm install netlify-cli -g
netlify deploy
```
Then choose `build` as the path to deploy.
To set up continuous delivery:
- Start a new Netlify project
- Pick your Git hosting service and select your repository
- Click "Build your site"
## API Calls
### Introduction
A standard use case for code actions is to engage with external services via API calls. AppStack uses the Axios library for making XMLHttpRequests from the browser. Axios Mock Adapter is also integrated which allows to mock these requests.
### Axios
#### Make a GET request
```javascript
axios.get('/api/user?id=12345')
.then(function (response) {
// handle success
console.log(response);
})
.catch(function (error) {
// handle error
console.log(error);
});
```
#### Perform a POST request
```javascript
axios.post('/api/user', {
firstName: 'Fred',
lastName: 'Flintstone'
})
.then(function (response) {
// handle success
console.log(response);
})
.catch(function (error) {
// handle error
console.log(error);
});
```
### Axios Mock Adapter
Axios adapter allows to easily mock requests.
#### Mock a GET request
```javascript
mock.onGet("/api/user").reply((config) => {
return [
200,
{
users: [{ id: 12345, firstName: "Fred", lastName: "Flintstone" }],
},
];
});
```
#### Mock a POST request
```javascript
mock.onPost("/api/user").reply((config) => {
const { firstName, lastName } = JSON.parse(config.data);
if (firstName && lastName) {
return [200, {
id: "12345",
firstName: "Fred",
lastName: "Flintstone",
}];
}
return [400, { message: "Looks like you didn't provide the required data." }];
});
```
## Redux
### Introduction
Redux aids in writing applications that behave consistently, run in different environments (client, server, native), and are easy to test. AppStack leverages Redux Toolkit to minimize the boilerplate code and complexity.
### Usage
AppStack has specific directories/files to store Redux logic:
- `src/redux/store.js`: Where reducers are combined and the store is initialized.
- `src/redux/slices/`: Where reducers are implemented.
#### 1. Creating a new slice
To create a new slice, simply add a file to the `src/redux/slices/` directory:
```javascript
import { createSlice } from '@reduxjs/toolkit';
const initialState = {
products: []
};
const slice = createSlice({
name: 'products',
initialState,
reducers: {
setProducts(state, payload) {
state.products = [
{
id: '1',
slug: 'my-first-product',
title: 'My first product'
}
];
}
}
});
export const { reducer } = slice;
export default slice;
export function getProducts() {
return async dispatch => {
const response = await axios.get('/api/products');
dispatch(slice.actions.setProducts(response.data.products));
};
}
```
#### 2. Add slice to root reducer
Open the file `src/redux/store.js` and add your new slice:
```javascript
import productsReducer from "./slices/products";
export const store = configureStore({
reducer: {
products: productsReducer,
},
});
```
#### 3. Using the slice
```jsx
import { useDispatch, useSelector } from 'react-redux';
import { getProducts } from '../redux/slices/products';
function ProductList() {
const dispatch = useDispatch();
const { products } = useSelector((state) => state.products);
useEffect(() => {
dispatch(getProducts());
}, [dispatch]);
return (
<div>
{products.map((product) => (
<div key={product.id}>
<div>{product.title}</div>
</div>
))}
</div>
);
}
```
### Redux DevTools
[Redux DevTools](https://github.com/reduxjs/redux-devtools) offers developer tools to power-up Redux development workflow or any other architecture which handles the state. It can be used as a browser extension (for Chrome, Firefox and Edge), or as a standalone app or as a React component integrated in the client app.
## Internationalization
### Introduction
react-i18next is a powerful internationalization framework for React based on i18next. It provides several components to ensure needed translations get loaded and your content gets rendered when the language changes.
Translations can be configured in the `/src/i18n.js` file:
```javascript
const resources = {
en: {
translation: {
"Welcome back": "Welcome back",
},
},
fr: {
translation: {
"Welcome back": "Bon retour",
},
},
de: {
translation: {
"Welcome back": "Willkommen zurück",
},
},
};
```
### Usage with hooks
You can utilize hooks in functional components. Here's an example:
```jsx
import React from 'react';
import { useTranslation } from 'react-i18next';
function MyComponent() {
const { t } = useTranslation();
return <h1>{t('Welcome back')}</h1>
}
```
### Usage with HOC
Alternatively, you can also use Higher Order Components (HOC) to extend existing components by passing additional props:
```jsx
import React from 'react';
import { withTranslation } from 'react-i18next';
function MyComponent({ t }) {
return <h1>{t('Welcome back')}</h1>
}
export default withTranslation()(MyComponent);
```
### Learn More
To learn more about react-i18next, click [here](<https://react.i18next.com/>)
## ESLint & Prettier
### Introduction
To format code automatically, we've included a basic ESLint & Prettier configuration. ESLint statically analyzes your code to quickly find problems. Prettier is used to automatically format the code you write to ensure a consistent code style withing your projects.
Included ESLint configuration:
```json
{
"extends": ["react-app", "prettier"],
"plugins": ["prettier"],
"rules": {
"prettier/prettier": "error"
}
}
```
### Usage
Format all source files in the `/src` folder:
```bash
npm run lint
```
### VSCode integration
To use ESLint & Prettier in combination with VSCode, we suggest installing the VSCode ESLint extension. After installing the extension, the code will automatically be formatted. The following configuration is included, which can be enabled/disabled or adjusted to your needs.
```json
{
"editor.defaultFormatter": "esbenp.prettier-vscode",
"editor.formatOnType": true,
"editor.formatOnSave": true,
"editor.formatOnPaste": true,
"editor.codeActionsOnSave": {
"source.fixAll.eslint": true
}
}
```
## Migrating to Next.js
### Introduction
AppStack React is built using Vite. Follow the steps below to migrate to Next.js. Migrating to Next.js allows you to use SSR, API Routes and more.
### Official Guide
The official guide on how to migrate from Create React App to Next.js can be found [here](<https://nextjs.org/docs/migrating/from-create-react-app>). While we're using Vite instead of Create React App, the process and steps are very similar.
### Update dependencies
The first step towards migrating to Next.js is to update package.json and dependencies.
Remove the `vite`, `@vitejs/plugin-react` and `react-router-dom` dependencies.
```bash
npm uninstall vite @vitejs/plugin-react vite-plugin-ejs vite-plugin-node-polyfills vite-plugin-svgr react-router-dom
```
Install the `next.js` dependency.
```bash
npm install next --save
```
Open the `package.json` file and replace the scripts with:
```json
"scripts": {
"dev": "next dev",
"build": "next build",
"start": "next start"
}
```
### Update entry file
Vite uses the root directory for the entry HTML file (`/index.html`), whereas Next.js uses a custom file (`/src/pages/_document.js`).
All code in the `<head>` section of the `/index.html` file should be moved to the `/src/pages/_document.js` file. Learn more [here](<https://nextjs.org/docs/advanced-features/custom-document>).
### Update shared layout
Vite uses the `/src/index.js` file as an entry point, whereas Next.js requires a custom `/src/_app.js` file. You may want to move logic to the new _app.js file. Learn more [here](<https://nextjs.org/docs/advanced-features/custom-app>).
### Update routes
With Vite, you're likely using React Router. Instead of using a third-party library, Next.js includes its own file-system based routing.
- Convert all Route components to new files in the `src/pages` directory. It is recommended to rename the files using dash-case.
- Remove useRoutes from the `/src/App.js file`.
- Replace the Link component from `react-router-dom` with the Link component from `next/link`.
For more information, see [Migrating from React Router](<https://nextjs.org/docs/migrating/from-react-router>).
| AppStack: Fully-featured Dashboard Template based on React & Bootstrap | appstack,dashboard,free,javascript,react,template,typescript,bootstrap,admin-dashboard,react-bootstrap | 2024-04-25T14:30:32Z | 2024-04-29T20:31:15Z | null | 1 | 0 | 3 | 0 | 2 | 6 | null | null | TypeScript |
tgerboui/nona-lib | main | # Nona Lib
[](https://github.com/tgerboui/nona-lib/actions/workflows/test.yml)
[](https://codecov.io/gh/tgerboui/nona-lib)
[](https://github.com/tgerboui/nona-lib/blob/main/LICENSE)
Nona Lib is a powerful and user-friendly TypeScript library designed to simplify interactions with the Nano cryptocurrency network.
Whether you're developing wallet software, integrating Nano payments into your application, or just exploring the possibilities of Nano's block lattice structure, Nona Lib provides a comprehensive set of tools to manage accounts, perform transactions, and query blockchain data efficiently and securely through your Nano node.
**Keys Features**
- **Easy Wallet Management**: Manage Nano accounts effortlessly, with functions to create, open, send and receive transactions.
- **Real-Time Updates via Websocket**: Utilize websockets for real-time transaction reception, confirmation tracking, and more.
- **Type Safe**: Fully implemented in TypeScript, providing strong type safety and seamless integration with TypeScript projects.
## Table of contents
- [Installation](#installation)
- [Getting Started](#getting-started)
- [Basic Usage](#basic-usage)
- [Nona API](#nona-api)
- [Handling Errors](#handling-errors)
- [Disclaimer](#disclaimer)
- [Roadmap](#roadmap)
## Installation
> [!NOTE]
> Before you begin using Nona Lib, ensure that your Nano node's `enable_control` is set to true, as the library requires this permission to perform certain operations.
> More information on how to configure your node can be found [here](https://docs.nano.org/running-a-node/configuration/#enable-control).
To install Nona Lib, run the following command in your project directory:
```bash
npm install nona-lib
```
## Getting Started
If your node runs on localhost with the default port:
```typescript
import { Nona } from 'nona-lib';
const nona = new Nona();
```
If your node runs on a custom port or on a remote server, you can specify the URLs:
```typescript
import { Nona } from 'nona-lib';
const nona = new Nona({
url: 'http://localhost:7076',
websocketUrl: 'ws://localhost:7078',
});
```
## Basic Usage
### Create an account
You can simply create a new account with the following code:
```typescript
const { privateKey, publicKey, address } = await nona.key.create();
```
Or from a seed:
```typescript
// Use KeyService to generate a seed or provide your own
const seed = await KeyService.generateSeed();
const { privateKey, publicKey, address } = await nona.key.create(seed);
```
These keys are generated locally using the [nanocurrency-js](https://github.com/marvinroger/nanocurrency-js/tree/master/packages/nanocurrency) package.
### Open an account
Before using an account, you need to open it.
To open an account, you must have sent some funds to it from another account.
Then call the open method:
```typescript
// You must provide a representative address to open the account
const reprensentative = 'nano_3rep...';
const wallet = nona.wallet(privateKey);
await wallet.open(reprensentative);
```
If you don't know how to choose a representative, check out this blog post: [How to choose a representative](https://nano.org/en/blog/how-to-choose-your-nano-representative--74f4c8c4).
### Send a transaction
To send a transaction, you must have an opened account (see [Open an account](#open-an-account)).
```typescript
const receveiver = 'nano_1rece...';
const amount = 2;
const wallet = nona.wallet(privateKey);
await wallet.send(receveiver, amount);
```
### Receive a transaction
To receive a transaction, you must have an opened account (see [Open an account](#open-an-account)).
To receive a single transaction:
```typescript
const wallet = nona.wallet(privateKey);
await wallet.receive();
```
If you want to receive all pending transactions:
```typescript
const wallet = nona.wallet(privateKey);
await wallet.receiveAll();
```
You can also listen and receive transactions in real time:
```typescript
const wallet = nona.wallet(privateKey);
// This will create a websocket connection, listen for incoming transactions, and automatically receive them.
const subscription = await wallet.listenAndReceive({
// (Optional) next will be called each time a transaction is received
next: (transactionBlock) => console.log('Received transaction', transactionBlock),
});
// Don't forget to unsubscribe when you don't need it anymore
subscription.unsubscribe();
```
For more details about websocket, see [Websocket](#websocket).
## Nona API
- [Wallet](#wallet)
- [Open](#open)
- [Send](#send)
- [Receive](#receive)
- [Receive all](#receive-all)
- [Listen and receive](#listen-and-receive)
- [Account](#account)
- [Receivable](#receivable)
- [Account info](#account-info)
- [Balance](#balance)
- [Listen confirmation](#listen-confirmation)
- [History](#history)
- [Block count](#block-count)
- [Representative](#representative)
- [Weight](#weight)
- [Websocket](#websocket)
- [Confirmation](#confirmation)
- [Blocks](#blocks)
- [Count](#count)
- [Create block](#create-block)
- [Process block](#process-block)
- [Block info](#block-info)
- [Key](#key)
- [Create](#create)
- [Expand](#expand)
- [Key Service](#key-service)
- [Generate seed](#generate-seed)
- [Get private key](#get-private-key)
- [Get public key](#get-public-key)
- [Get address](#get-address)
- [Node](#node)
- [Telemetry](#telemetry)
- [Uptime](#uptime)
- [Version](#version)
- [Rpc](#rpc)
- [Name Service](#name-service)
- [Resolve Username](#resolve-username)
- [Resolve Target](#resolve-target)
- [Datatypes](#datatypess)
- [Nano Address](#nano-address)
- [Nano Username](#nano-username)
- [Nano Target](#nano-target)
## Wallet
> [!NOTE]
> All methods in the [account API](#account) are also available via the wallet object.
> [!WARNING]
> This wallet API does not interact with the [wallet RPCs commands](https://docs.nano.org/commands/rpc-protocol/#wallet-rpcs) this naming is only for convenience.
The wallet is the main object to interact with your account.
```typescript
const wallet = nona.wallet(privateKey);
```
### Open
```typescript
open(representative: NanoTarget): Promise<string>
```
Opens the account with the provided representative represented as a [NanoTarget](#nano-target) string.
The first transaction of an account is crafted in a [slightly different way](https://docs.nano.org/integration-guides/key-management/#first-receive-transaction). To open an account, you must have sent some funds to it from another account.
Returns the hash of the transaction.
```typescript
const representative = 'nano_3rep...';
await wallet.open(representative);
```
### Send
```typescript
send(target: NanoTarget, amount: number | string): Promise<string>
```
Sends a transaction to the specified [target](#nano-target).
The amount is in nano unit.
Returns the hash of the transaction.
```typescript
const address = 'nano_1rece...';
const amount = 2;
await wallet.send(address, amount);
```
> [!NOTE]
> The work is generated by the node, the options to provide or generate the work locally are not yet implemented.
### Receive
```typescript
receive(hash?: string): Promise<string | null>
```
Receives a pending transaction.
The hash of the transaction to receive can be provided. If not, a receivable hash will be used.
Returns the hash of the receive block.
If no hash is provided and no transaction is pending, `null` is returned.
```typescript
await wallet.receive();
```
An hash can also be provided to receive a specific transaction:
```typescript
const hash = 'D83124BB...';
await wallet.receive(hash);
```
### Receive all
```typescript
receiveAll(hashes?: string[]): Promise<string[]>
```
Receives all pending transactions.
Returns an array of hashes of the received blocks.
```typescript
await wallet.receiveAll();
```
An array of hashes can also be provided to receive specific transactions:
```typescript
const hashes = ['D83124BB...', '1208FF64...'];
await wallet.receiveAll(hashes);
```
### Listen and receive
> [!NOTE]
> All the webscoket related methods use Rxjs Observables and return a Subscription object. For more information about observables and subscriptions, see the [Rxjs documentation](https://rxjs.dev/).
```typescript
listenAndReceive(params?: WalletListAndReceiveParams): Subscription
```
Listens for incoming transactions and automatically receives them.
Return a [Subscription](https://rxjs.dev/guide/subscription) object.
```typescript
interface WalletListAndReceiveParams {
/**
* A function that will be called each time a transaction is received.
* @param block The block that was received.
*/
next?: (block: ConfirmationBlock) => unknown;
/**
* A function that will be called when an error occurs.
* @param error The error that occurred.
*/
error?: (error: unknown) => unknown;
/**
* A function that will be called when the listener completes.
*/
complete?: () => unknown;
}
```
```typescript
const subscription = await wallet.listenAndReceive({
next: (transactionBlock) => console.log('Received transaction', transactionBlock),
error: (error) => console.error('An error occurred', error),
complete: () => console.log('Subscription completed'),
});
// Don't forget to unsubscribe when you don't need it anymore
subscription.unsubscribe();
```
> [!WARNING]
> Depending on the node setup and sync status, multiple confirmation notifications for the same block hash may be sent by a single tracking mechanism.
> Theses block will call the `error` function with the error `Unreceivable`.
## Account
> [!NOTE]
> Theses commands are also available using the [wallet](#wallet) object.
All commands related to public account information.
You can create an account object with the following code:
```typescript
const address = 'nano_13e2ue...';
const account = await nona.account(address);
```
You can also use your [wallet](#wallet) object:
```typescript
const wallet = nona.wallet(privateKey);
````
### Receivable
```typescript
receivable(params?: ReceivableParams): Promise<Receivable>
```
Returns a list of block hashes which have not yet been received by this account.
```typescript
interface ReceivableParams {
/**
* Specifies the number of blocks to return.
* Default to 100.
*/
count?: number;
/**
* Specifies whether to sort the response by block amount.
* Default to false.
*/
sort?: boolean;
}
```
Depending on the `sort` parameter, the blocks will be returned in two different ways.
If `sort` is `false` (default), the blocks will be returned as an array of strings:
```typescript
const receivable = await account.receivable();
console.log(receivable);
// ['D83124BB...', '1208FF64...', ...]
```
If `sort` is `true`, the blocks will be returned as an object with the block hash as the key and the amount as the value:
```typescript
const receivable = await account.receivable({ sort: true });
console.log(receivable);
// { 'D83124BB...': 2, '1208FF64...': 1, ... }
```
### Account info
```typescript
info(params?: InfoParams): Promise<AccountInfo>
```
Returns general information for account.
Only works for accounts that have received their first transaction and have an entry on the ledger, will return "Account not found" otherwise.
To open an account, use [open](#open).
```typescript
interface InfoParams {
/**
* Specifies whether to include the representative in the response.
* Default to false.
*/
representative?: boolean;
/**
* Specifies whether to return the raw balance.
* Default to false.
*/
raw?: boolean;
}
````
```typescript
const info = await account.info();
console.log(info);
// {
// frontier: '0D60C42554478A2EDAD18AD5E975422297E62082E612C60ECABBDD4D01B65D46',
// open_block: '92CBCAC62345F58A58CE513652D22BD6E13CB094BF6F8D825DEE01CE54718868',
// representative_block: '0D60C42253478E2ADAD18AD5E975426297E62082E612C60ECAACDD4D01B65D46',
// balance: '2.3',
// modified_timestamp: '1712846889',
// block_count: '82',
// account_version: '2',
// confirmation_height: '82',
// confirmation_height_frontier: '0D60C22554478E2EDAD81BD5E975426297E62082E612C60ECAACDD4D01B65D46'
// }
```
### Balance
```typescript
balance({ raw = false }: { raw?: boolean }): Promise<AccountBalance>
```
Returns how many nano is owned and how many have not yet been received by account.
Set `raw` to `true` to return the balance in raw unit.
```typescript
const balance = await account.balance();
console.log(balance);
// { balance: '2.3', receivable: '5', pending: '0' }
```
`balance` is the total amount of nano owned by the account.
`receivable` is the amount of nano that has not yet been received by the account.
> [!NOTE]
> `pending` was deprecated in favor of `receivable`. For compatibility reasons both terms are still available for many calls and in responses.
> For more details see: https://docs.nano.org/releases/release-v24-0/#pendingreceivable-term-rpc-updates.
### Listen confirmation
```typescript
listenConfirmation(params: ListenConfirmationParams): Subscription
```
Listen for all confirmed blocks for the related account.
```typescript
export interface ListenConfirmationParams {
/**
* A function that will be called each time a transaction is received.
* @param block The block that was received.
*/
next: (block: ConfirmationBlock) => unknown;
/**
* A function that will be called when an error occurs.
* @param error The error that occurred.
*/
error?: (error: unknown) => unknown;
/**
* A function that will be called when the listener completes.
*/
complete?: () => unknown;
/**
* A filter that will be used to filter the confirmation blocks.
*/
filter?: ConfirmationFilter;
}
export interface ConfirmationFilter {
/** List of block subtypes to filter the confirmation blocks. */
subtype?: string[];
/** Account addresses that received the transaction. */
to?: NanoAddress[];
}
````
Listen all sent confirmation blocks for the account from a specific address:
```typescript
const subscription = await account.listenConfirmation({
next: (transactionBlock) => console.log('Received confirmation', transactionBlock),
filter: {
accounts: ['nano_1send...'],
subtype: ['send']
},
});
```
> [!WARNING]
> Depending on the node setup and sync status, multiple confirmation notifications for the same block hash may be sent by a single tracking mechanism.
> In order to prevent potential issues, integrations must track these block hashes externally to the node and prevent any unwanted actions based on multiple notifications.
### History
```typescript
history(params?: AccountHistoryParams): Promise<AccountHistory>
```
Retrieves the account history.
Returns only send & receive blocks by default (unless raw is set to true - see optional parameters below): change, state change & state epoch blocks are skipped, open & state open blocks will appear as receive, state receive/send blocks will appear as receive/send entries.
Response will start with the latest block for the account (the frontier), and will list all blocks back to the open block of this account when "count" is set to "-1".
```typescript
export interface AccountHistoryParams {
/** Number of blocks to return. Default to 100. */
count?: number;
/** Hash of the block to start from. */
head?: string;
/** Number of blocks to skip. */
offset?: number;
/** Reverse order */
reverse?: boolean;
/** Results will be filtered to only show sends/receives connected to the provided account(s). */
accounts?: NanoAddress[];
/**
* if set to true instead of the default false, returns all blocks history and output all parameters of the block itself.
*/
raw?: boolean;
}
```
```typescript
const history = await account.history();
console.log(history);
// {
// history: [
// {
// type: 'send',
// account: 'nano_13dtu...',
// amount: '1.23',
// hash: 'C43ED22C09...',
// local_timestamp: '1712846889',
// height: '82',
// },
// [...]
// ],
// previous: 'D83124BB...',
// }
```
To paginate the history, you can use the `head` parameter with the `previous` value from the previous call:
```typescript
let hasNext = true;
let head: string | undefined;
while (hasNext) {
const { history, previous } = await account.history({ head });
console.log(history);
if (previous) {
head = previous;
} else {
hasNext = false;
}
}
```
If `reverse` is `true`, use `next` instead of `previous`.
### Block count
```typescript
blockCount(): Promise<number>
```
Returns the number of blocks for this account.
```typescript
const blockCount = await account.blockCount();
console.log(blockCount);
// 42
```
### Representative
```typescript
representative(): Promise<string>
```
Returns the representative for this account.
```typescript
const representative = await account.representative();
console.log(representative);
// nano_3rep...
```
### Weight
```typescript
weight(): Promise<string>
```
Returns the voting weight for this account in nano unit (default).
```typescript
const weight = await account.weight();
console.log(weight);
// 123.456789
```
Set `raw` to `true` to return the weight in raw unit.
```typescript
const weight = await account.weight({ raw: true });
console.log(weight);
// 123456789000000000000000000000000
```
## Websocket
> [!NOTE]
> All the webscoket related methods use Rxjs Observables and return a Subscription object. For more information about observables and subscriptions, see the [Rxjs documentation](https://rxjs.dev/).
At the first subscription, the websocket connection to the node will be established.
If all subscriptions are unsubscribed, the connection will be closed.
You can access to the websocket object with the following code:
```typescript
const ws = nona.ws;
```
### Confirmation
```typescript
confirmation(params: WebSocketConfirmationParams): Subscription
```
Listens for confirmed blocks.
Return a [Subscription](https://rxjs.dev/guide/subscription) object.
```typescript
interface WebSocketConfirmationParams {
/**
* A function that will be called each time a transaction is received.
* @param block The block that was received.
*/
next: (block: ConfirmationBlock) => unknown;
/**
* A function that will be called when an error occurs.
* @param error The error that occurred.
*/
error?: (error: unknown) => unknown;
/**
* A function that will be called when the listener completes.
*/
complete?: () => unknown;
/**
* A filter that will be used to filter the confirmation blocks.
*/
filter?: ConfirmationFilter;
}
interface ConfirmationFilter {
/** List of account addresses to filter the confirmation blocks. */
accounts?: NanoAddress[];
/** List of block subtypes to filter the confirmation blocks. */
subtype?: string[];
/** Account addresses that received the transaction. */
to?: NanoAddress[];
}
```
Subscribe to all new confirmed blocks on the network:
```typescript
const subscription = await nona.ws.confirmation({
// next will be called each time a transaction is received
next: (confirmationBlock) => console.log('Received confirmation', confirmationBlock),
});
// Don't forget to unsubscribe when you don't need it anymore
subscription.unsubscribe();
```
Subscribe to all new sent confirmation blocks to a specific account:
```typescript
const subscription = await nona.ws.confirmation({
next: (block) => console.log('Received confirmation', block),
filter: {
subtype: ['send'],
to: ['nano_1send...'],
},
});
```
## Blocks
You can access to the blocks object with the following code:
```typescript
const blocks = nona.blocks;
```
### Count
```typescript
count(): Promise<BlockCount>
```
Reports the number of blocks in the ledger and unchecked synchronizing blocks.
This count represent the node ledger and not the network status.
```typescript
const count = await blocks.count();
console.log(count);
// { count: '198574599', unchecked: '14', cemented: '198574599' }
```
`count` - The total number of blocks in the ledger. This includes all send, receive, open, and change blocks.
`unchecked` - The number of blocks that have been downloaded but not yet confirmed. These blocks are waiting in the processing queue.
`cemented` - The number of blocks that have been confirmed and cemented in the ledger. Cemented blocks are confirmed irreversible transactions.
### Create block
> [!WARNING]
> This method is for advanced usage, use it if you know what you are doing.
```typescript
create(params: CreateBlockParams): Promise<string>
```
Creates a block object based on input data & signed with private key or account in wallet.
Create a send block.
Let's say you want to send 1 nano to `nano_1send...`.
You have currently 3 nano in your account.
```typescript
const wallet = nona.wallet(privateKey);
const info = await wallet.info();
const recipient = 'nano_1send...';
const recipientPublicKey = KeyService.getPublicKey(recipient);
const sendBlock = await this.blocks.create({
// Current account
account: wallet.address,
// Final balance for account after block creation in raw unit (here: current balance - send amount).
balance: '2000000000000000000000000000000',
// The block hash of the previous block on this account's block chain ("0" for first block).
previous: info.frontier,
// The representative account for the account.
representative: info.representative,
// If the block is sending funds, set link to the public key of the destination account.
// If it is receiving funds, set link to the hash of the block to receive.
// If the block has no balance change but is updating representative only, set link to 0.
link: recipientPublicKey,
// Private key of the account
key: privateKey,
});
```
### Process block
> [!WARNING]
> This method is for advanced usage, use it if you know what you are doing.
```typescript
process(block: Block, subtype: string): Promise<string>
```
Publish it to the network.
Returns the hash of the published block.
If we want to process the block created in the previous example:
```typescript
await this.blocks.process(sendBlock, 'send');
```
### Block info
```typescript
info(hash: string): Promise<BlockInfo>
```
Retrieves information about a specific block.
```typescript
const hash = 'D83124BB...';
const info = await blocks.info(hash);
```
## Key
You can access to the key object with the following code:
```typescript
const blocks = nona.key;
```
### Create
> [!NOTE]
> The keys are generated locally using the [nanocurrency-js](https://github.com/marvinroger/nanocurrency-js/tree/master/packages/nanocurrency) package.
```typescript
create(seed?: string): Promise<AccountKeys>
```
Create keys for an account.
```typescript
const { privateKey, publicKey, address } = await nona.key.create();
```
### Expand
```typescript
expand(privateKey: string): AccountKeys
```
Expand a private key into public key and address.
```typescript
const { publicKey, address } = nona.key.expand(privateKey);
```
## Key Service
Service to generate seeds and keys.
### Generate seed
```typescript
KeyService.generateSeed(): Promise<string>
```
Generates a random seed.
```typescript
const seed = await KeyService.generateSeed();
```
### Get private key
```typescript
KeyService.getPrivateKey(seed: string, index: number): string
```
Derive a private key from a seed, given an index.
```typescript
const privateKey = KeyService.getPrivateKey(seed, 0);
```
### Get public key
```typescript
KeyService.getPublicKey(privateKeyOrAddress: string): string
```
Derive a public key from a private key or an address.
```typescript
const publicKey = KeyService.getPublicKey(privateKey);
```
### Get address
```typescript
KeyService.getAddress(publicKey: string): string
```
Derive an address from a public key.
```typescript
const address = KeyService.getAddress(publicKey);
```
## Node
You can access to the node object with the following code:
```typescript
const node = nona.node;
```
### Telemetry
```typescript
telemetry(): Promise<Telemetry>
```
Return metrics from other nodes on the network.
Summarized view of the whole network.
```typescript
const telemetry = await node.telemetry();
```
### Uptime
```typescript
uptime(): Promise<number>
```
Return node uptime in seconds.
```typescript
const uptime = await node.uptime();
console.log(uptime);
// 832870
```
### Version
```typescript
version(): Promise<Version>
```
Returns version information for RPC, Store, Protocol (network), Node (Major & Minor version).
```typescript
const version = await node.version();
```
## Rpc
if you prefer to call RPC directly you can use `nona.rpc`.
```typescript
rpc(action: string, body?: object): Promise<unknown>
```
Call `account_info` RPC command:
```typescript
const info = await nona.rpc('account_info', {
account: 'nano_13e2ue...',
});
```
## Name Service
You can access to the `nameService` object with the following code:
```typescript
const nameService = nona.nameService;
```
### Resolve Username
```typescript
resolveUsername(username: NanoUsername): Promise<NanoAddress>
```
Resolves a username registered with the [Nano Name Service](https://nano.to) to the registed [NanoAddress](#nano-address)
```typescript
const username = '@nona-lib';
const address = await nona.nameService.resolveUsername(username);
```
### Resolve Target
```typescript
resolveTarget(target: NanoTarget): Promise<NanoAddress>
```
Takes in a [NanoTarget](#nano-target) to potentially resolve. It checks if the target is a valid [NanoAddress](#nano-address) or a [NanoUsername](#nano-username). In the case a [NanoUsername](#nano-username) is passed to the method, it is [automatically resolved](#resolve-username)
```typescript
const target = '@nona-lib';
const address = await nona.nameService.resolveTarget(target);
```
```typescript
const target = 'nano_1rece...';
const address = await nona.nameService.resolveTarget(target);
```
## Datatypes
### Nano Address
A valid Nano address according to the [offical docs](https://docs.nano.org/integration-guides/the-basics/#account-public-address):
```
nano_1anrzcuwe64rwxzcco8dkhpyxpi8kd7zsjc1oeimpc3ppca4mrjtwnqposrs
```
Its validity is checked with the [nanocurrency-js](https://github.com/marvinroger/nanocurrency-js/tree/master/packages/nanocurrency) package.
### Nano Username
A Nano username in the form of `@name`:
```
@nona-lib
```
This username is resolved at runtime with the [Nano Name Service](https://nano.to).
### Nano Target
A NanoTarget is either a valid [address](#nano-address) (e.g. `nano_1rece...`) or a resolveable username registered with the [Nano Name Service](https://nano.to) (e.g. `@nona-lib`). Nonalib automatically resolves these usernames to valid adresses for you.
## Handling Errors
All handled errors are instances of `NonaError`.
Each types of errors are extended from `NonaError` and have a specific instance.
`NonaError` - Base class for all errors and generic error.
`NonaNetworkError` - Network error, likely related to the node connection.
`NonaRpcError` - Error related to the RPC call response.
`NonaParseError` - Error related to the response parsing.
If this occured while using the library, please report it.
`NonaUserError` - Error related to the user input.
For example, if you try to send a transaction with an insufficient balance:
```typescript
try {
await wallet.send('nano_1rece...', 100);
} catch (error) {
if (error instanceof NonaUserError && error.message === 'Insufficient balance') {
console.log('You don\'t have enough balance to send this amount');
} else {
console.error('An error occurred', error);
}
}
```
## Disclaimer
Nona Lib is a young and evolving TypeScript library designed to interact with the Nano cryptocurrency network. While we strive to ensure reliability and robustness, the following points need to be considered:
- **Early-stage Software**: As an early-stage library, Nona Lib may undergo significant changes with updates that could improve or alter functionalities drastically. Users are advised to keep this in mind when using the library in production environments.
- **Limited Usage**: Given its nascent stage, the library has been subjected to limited usage. This means there could be undiscovered bugs or issues affecting its performance and reliability. We welcome contributions and reports on any anomalies found during usage.
- **Dependency on External Systems**: Nona Lib operates in conjunction with external systems such as Nano nodes, and its performance is highly dependent on the configuration and stability of these systems.
- **Security Risks**: As with any tool managing financial transactions, there is an inherent risk. Users should be cautious and test thoroughly when integrating and deploying Nona Lib in security-sensitive environments.
We encourage the community to contribute to the development and testing of Nona Lib to help us improve its functionality and security. Use this library with caution, and ensure you have robust backup and recovery processes in place.
## Roadmap
### Websocket
- [x] Confirmation
- [ ] Custom filter
- [ ] Vote
- [ ] Start/stop election
- [ ] Active difficulty
- [ ] Proof of work
- [ ] New unconfirmed block
### Proof of work
- [ ] Custom work input
- [ ] Local work generation
- [ ] Custom work server URL
### External services
#### Nano.to
- [x] Integrate [Nano Name Service](https://github.com/fwd/nano-to)
- [ ] Integrate [rpc.nano.to](https://rpc.nano.to/) commands
### Tests
- [x] Create unit tests
- [ ] Create integration tests
| TypeScript library to simplify interactions with the Nano currency node. | browser,javascript,library,nano,nanocurrency,nodejs,rpc,typescript,websocket | 2024-03-19T20:04:59Z | 2024-05-09T10:33:42Z | 2024-05-09T10:33:42Z | 3 | 4 | 172 | 6 | 1 | 6 | null | MIT | TypeScript |
nousantx/tui-template-vue | main | # vue-tui
## Project setup
```
yarn install
```
### Add TenoxUI
```
yarn add tenoxui -D
```
### Compiles and hot-reloads for development
```
yarn serve
```
### Compiles and minifies for production
```
yarn build
```
### Lints and fixes files
```
yarn lint
```
### Customize configuration
See [Configuration Reference](https://cli.vuejs.org/config/).
| VueJS App template with tenoxui | css-framework,design,frontend,javascript,template,ui,ui-components,vue,vue-template-project,vuejs | 2024-04-15T02:54:17Z | 2024-04-15T02:53:10Z | null | 1 | 0 | 2 | 0 | 0 | 6 | null | null | Vue |
BryanBerger98/eslint-config-bryanberger | main | # eslint-config-bryanberger
This package provides my personal .eslintrc as an extensible shared config.
## Usage
I export five ESLint configurations for your usage.
### eslint-config-bryanberger
My default export contains most of my ESLint rules, including ECMAScript 6+, TypeScript and React. It requires `eslint`, `eslint-plugin-import`, `@typescript-eslint/eslint-plugin`, `@typescript-eslint/parser`, `eslint-import-resolver-typescript`, `eslint-plugin-react`, `eslint-plugin-react-hooks`, and `eslint-plugin-jsx-a11y`.
#### Install the correct versions of each package
```sh
npx install-peerdeps --dev eslint-config-bryanberger
```
#### Extends config
Add `"extends": "bryanberger"` to your `.eslintrc` to extend the entire configuration.
If you only want to extend one of my configurations, your can only add `"extends": "bryanberger/$CONFIG_NAME"` to your `.estlinrc`. Here is the configurations list:
* `bryanberger/javascript`
* `bryanberger/typescript`
* `bryanberger/imports`
* `bryanberger/react`
You can extend multiple selected configs with the following syntax:
```json
{
"extends": [
"bryanberger/javascript",
"bryanberger/react"
]
}
```
| My personal eslint config | eslint,eslint-config,eslintrc,javascript,react,typescript | 2024-03-28T17:43:57Z | 2024-04-03T06:01:04Z | 2024-04-03T06:01:04Z | 2 | 1 | 24 | 0 | 0 | 6 | null | MIT | JavaScript |
djangir/nodejs-project-structure | main | null | Great start! Establish a Node.js project structure with folders like 'src' for source code, containing 'index.js' as the entry point, along with subfolders for controllers, models, routes, and utilities. Ensure 'package.json' for dependencies. This organized layout streamlines development, enhancing readability and maintainability. | classes-in-javascript,code,node,nodejs,project,scalling,structure,core,javascript,node-js | 2024-04-18T02:27:08Z | 2024-05-02T03:26:32Z | null | 1 | 0 | 23 | 0 | 1 | 6 | null | null | JavaScript |
filipmariania/Shopify-liquid-ajax-cart | main | # Build a Shopify Ajax-cart without JavaScript coding :fire:
[](https://www.npmjs.com/package/liquid-ajax-cart)  
Ajaxifies Shopify cart sections and product forms.
Doesn't apply CSS styles — the appearance is up to a developer.
No JavaScript code needed — just plain Liquid.
## 3-Step installation
##### 1. Create a theme section for the cart with a `data-ajax-cart-section` container
```html
{% comment %} sections/my-cart.liquid {% endcomment %}
<form action="{{ routes.cart_url }}" method="post" class="my-cart">
<!-- Add the data-ajax-cart-section attribute
to a container that must be re-rendered
when the user's cart gets changed -->
<div data-ajax-cart-section>
<h2>Cart</h2>
<div class="my-cart__items" data-ajax-cart-section-scroll>
{% for item in cart.items %}
{% assign item_index = forloop.index %}
<hr />
<div><a href="{{ item.url }}">{{ item.title }}</a></div>
<div>Price: {{ item.final_price | money }}</div>
<div>
Quantity:
<!-- Wrap the quantity control in the <ajax-cart-quantity> custom tag -->
<ajax-cart-quantity>
<!-- Add the data-ajax-cart-quantity-minus attribute to the "Minus" button -->
<a data-ajax-cart-quantity-minus
href="{{ routes.cart_change_url }}?line={{ item_index }}&quantity={{ item.quantity | minus: 1 }}" >
Minus one
</a>
<!-- Add the data-ajax-cart-quantity-input attribute to quantity input fields -->
<input data-ajax-cart-quantity-input="{{ item_index }}" name="updates[]" value="{{ item.quantity }}" type="number" />
<!-- Add the data-ajax-cart-quantity-plus attribute to the "Plus" button -->
<a data-ajax-cart-quantity-plus
href="{{ routes.cart_change_url }}?line={{ item_index }}&quantity={{ item.quantity | plus: 1 }}">
Plus one
</a>
</ajax-cart-quantity>
</div>
<!-- Place a data-ajax-cart-errors container for error messages -->
<div data-ajax-cart-errors="{{ item.key }}"></div>
<div>Total: <strong>{{ item.final_line_price | money }}</strong></div>
{% endfor %}
</div>
<button type="submit" name="checkout">
Checkout — {{ cart.total_price | money_with_currency }}
</button>
</div>
</form>
{% schema %} { "name": "My Cart" } {% endschema %}
```
##### 2. Include the section and the `liquid-ajax-cart.js` in your theme.liquid
```html
{% comment %}
Put this code within <body> tag —
in a place where you want the ajax-cart section to appear
{% endcomment %}
{% section 'my-cart' %}
<script type="application/json" data-ajax-cart-initial-state >{{ cart | json }}</script>
<script type="module">
import '{{ 'liquid-ajax-cart.js' | asset_url }}';
</script>
```
##### 3. Wrap Shopify product forms in the <ajax-cart-product-form> custom tag
```html
<ajax-cart-product-form>
{% form 'product', product %}
<!-- form content -->
<div data-ajax-cart-errors="form"></div>
{% endform %}
</ajax-cart-product-form>
```
:tada: That's it!
Download the latest version of the `liquid-ajax-cart.js` from the [documentation](https://liquid-ajax-cart.js.org) website.
## The repository content
* `docs` folder — the [documentation](https://liquid-ajax-cart.js.org) website;
* `_src` folder — the library sources;
* `assets`, `config`, `layout`, `locales`, `sections`, `snippets`, `templates` folders — the [demo store](https://liquid-ajax-cart.myshopify.com) theme sources. The password of the store — `liquid-ajax-cart`.
| Build a Shopify Ajax-cart without JavaScript coding | ajax-cart,cart,ecommerce,javascript,shopify,shopify-cart,shopping-cart | 2024-04-07T02:06:26Z | 2024-01-24T11:50:38Z | null | 1 | 0 | 1,061 | 0 | 0 | 6 | null | null | Liquid |
jrTilak/lazykit | dev | <h1 align="center">
<br>
<a href="https://lazykit.thapatilak.com.np/"><img src="./src/www/public/logo.svg" alt="@jrtilak/lazykit" width="150"></a>
<br>
@jrtilak/lazykit
<br>
</h1>
<h4 align="center">Trim the fat, Keep the function</h4>
---
Refine your JavaScript workflows with Lazykit.
A concentrated collection of lean utility functions, not a bloated library.
## Documentation
Visit [here](https://lazykit.thapatilak.com.np/docs/introduction) for detailed documentation.
## Contributing
Visit [here](./docs/README.md) for contributing guidelines.
## License
Visit [here](./LICENSE) for license information.
## Some Useful Links
- [NPM Package](https://www.npmjs.com/package/@jrtilak/lazykit)
- [Develop Branch](https://lazykit-www-git-dev-tilak-thapas-projects.vercel.app/)
- [Master Branch](https://lazykit.thapatilak.com.np/)
Thank you for using Lazykit! <3
| Refine your JavaScript workflows with Lazykit. A concentrated collection of lean utility functions, not a bloated library. | javascript,jrtilak,typescript,utilities,lazykit | 2024-03-17T02:36:35Z | 2024-05-15T02:18:34Z | 2024-05-15T02:09:04Z | 5 | 58 | 229 | 14 | 2 | 6 | null | MIT | TypeScript |
sonnetjs/sonnet | main | # SonnetJS
A frontend framework for building modern web applications. SonnetJS is a collection of packages and tools that help you build web applications with ease.
## Usage
1. Run the following command to create a new SonnetJS project.
```bash
npx create-sonnet-app@latest
```
2. Change directory to the newly created project.
```bash
cd [my-sonnet-app]
```
3. Install the dependencies
```bash
npm i
```
4. Start the development server
```bash
npm run dev
```
## Apps and Packages
- `@sonnet/core`: The core package that provides the foundation for building web applications.
## NPM
SonnetJS is available on NPM. You can install the core package by running:
```bash
npm i @sonnetjs/core
```
## NPM Links
[https://npmjs.com/package/@sonnetjs/core](https://npmjs.com/package/@sonnetjs/core)
| Sonnetjs is an opinionated frontend framework for crafting web ui | framework,frontend,frontend-framework,javascript,js,monorepo,turbo,ui,web,web-ui | 2024-03-31T02:18:45Z | 2024-05-18T12:06:24Z | null | 1 | 0 | 80 | 0 | 0 | 6 | null | null | JavaScript |
CodeStrong2023/TercerSemestreBugBusters | main | # Tercer Semestre BugBusters
Repositorio del grupo BugBusters 👻 del 3er Semestre de la Tecnicatura en Programacio de la UTNFRSR
## Integrantes:
* _David Abadie_
* _Franco Pizarro_
* _Belén Limachi_
* _Nicolás Nuñez_
* _Marcos Senn_
* _Santiago Segura_
* _Facundo Mendez_
## Sobre este repositorio:
En este repositorio se encuentra todo el codigo 💻 de las actividades y tareas realizadas durante el cursado del tercer semestre de la tecnicatura en las materias de **Programación 3**, **Laboratorio 3** y demás materias.
## Metodología de trabajo:
| Mes 📆 | Scrum Master 👨💻👩💻|
|--------|------|
| Abril | Nicolás Núñez |
| Mayo | Santiago Segura |
| Junio | David Abadie |
| Agosto | Franco Pizarro |
| Septiembre | Belén Limachi |
| Octubre | Marcos Senn |
| Noviembre | Facundo Mendez |
- Cada Lunes se subirá al repositorio las clases trabajadas la semana anterior.
- Una vez por mes se hará el merge de la rama "develop" a la rama "main"
| Repositorio del grupo BugBusters - Tercer semestre Tecnicatura Universitaria en Programación UTNFRSR | java,javascript,python,scrum | 2024-04-04T13:13:03Z | 2024-05-06T16:53:28Z | 2024-04-30T16:25:43Z | 8 | 105 | 159 | 0 | 2 | 6 | null | null | Java |
Bhanu-code/db-drawer | main | # db-drawer
A cli tool for visualising your database schemas. db-drawer checks the data model schemas of your project ("./models") folder and visualises by running on localhost in node environment. it attaches to your project as an npm package.
Currently, we have support only for sequelize and mongoose.
Refer to Learn.md for building the project: <a href="https://github.com/Bhanu-code/db-drawer/blob/main/Learn.md">Learn.md</a>
Video demonstration of the project: <a href="https://youtu.be/bcp6hE_R75U?si=Rd8dj-SLtZwtVjwH">Demonstration video</a>
Join Our Discord channel: <a href="https://discord.gg/bgnvc7Wc">Discord</a>
## Installation
Install db-drawer with npm
### Local installation
```javascript
//Install as dev dependency in your project
npm install db-drawer --save-dev
//For sequelize
npx db-draw s
//For mongoose
npx db-draw m
```
### Global installation
```javascript
npm install -g db-drawer
cd /path/to/your/project
//For sequelize
db-draw s
//For mongoose
db-draw m
```
After executing the command, it will run localhost where you can see your schema, relationship and constraints in a tablular format
## Screenshots
## Local Setup
Note: [ Don't commit to main branch, always create a seprate branch before raising PR ]
```javascript
// You will need a demo project that has "/models" folder to see your models visualised.
//To setup the project locally, for the repository and copy the forked copy the https url
//In the terminal write
git clone [repo-url]
cd db-drawer
npm install
// Have a project that has "models" folder
//Install dbdrawer-mongo to the project globally
npm install -g
// Open the demo project
cd /path/to/your/project
//Run the command for sequelize
db-draw s
//Run the command for mongoose
db-draw m
```
Hit enter and it will run localhost where you can see your schema, relationship and constraints in a tablular format
Create a branch, make changes and raise PR
## Contributing
Contributions are always welcome!
See `contributing.md` for ways to get started.
Please adhere to this project's `code of conduct`.
## License
[MIT License](LICENSE)
| database schema visualization cli tool on localhost for node.js environment | cli,ejs,expressjs,javascript,mongoose,npm-package,sequelize,process-manager,girlscriptsummerofcode,gssoc24 | 2024-04-11T09:18:15Z | 2024-05-22T17:56:16Z | null | 12 | 22 | 61 | 18 | 14 | 6 | null | MIT | EJS |
filipmariania/Netflix-Clone-using-React | main | The stack that is being used: React (custom hooks, context, portals), Firebase (Firestore/auth), Compound & Styled components!
Hey! I finally finished this Netflix clone (took me more time than I expected 😅). My idea was to make everything static (movies, series, tv shows, ...) but then I found this really cool TMDB API which you can pull most popular movies, top rated shows, what's trending, collections, lists and muuuch more. Really worth checking the effort made.
First use the <b>Firebase App</b> api key of your's as the project's api keys has been removed and you can add them in /lib/firebase.prod.js file and <b>tmdb</b> api key also needs to be changed, which is present in request.js file under the project directory.
<img src="/images/demo1.png">
<img src="/images/demo2.png">
With Youtube Trailers Embeded
<img src="/images/demo3.png">
# Getting Started with Create React App
This project was bootstrapped with [Create React App](https://github.com/facebook/create-react-app).
## Available Scripts
In the project directory, you can run:
### `npm start`
Runs the app in the development mode.\
Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
The page will reload if you make edits.\
You will also see any lint errors in the console.
### `npm test`
Launches the test runner in the interactive watch mode.\
See the section about [running tests](https://facebook.github.io/create-react-app/docs/running-tests) for more information.
### `npm run build`
Builds the app for production to the `build` folder.\
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.\
Your app is ready to be deployed!
See the section about [deployment](https://facebook.github.io/create-react-app/docs/deployment) for more information.
### `npm run eject`
**Note: this is a one-way operation. Once you `eject`, you can’t go back!**
If you aren’t satisfied with the build tool and configuration choices, you can `eject` at any time. This command will remove the single build dependency from your project.
Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except `eject` will still work, but they will point to the copied scripts so you can tweak them. At this point you’re on your own.
You don’t have to ever use `eject`. The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.
## Learn More
You can learn more in the [Create React App documentation](https://facebook.github.io/create-react-app/docs/getting-started).
To learn React, check out the [React documentation](https://reactjs.org/).
### Code Splitting
This section has moved here: [https://facebook.github.io/create-react-app/docs/code-splitting](https://facebook.github.io/create-react-app/docs/code-splitting)
### Analyzing the Bundle Size
This section has moved here: [https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size](https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size)
### Making a Progressive Web App
This section has moved here: [https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app](https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app)
### Advanced Configuration
This section has moved here: [https://facebook.github.io/create-react-app/docs/advanced-configuration](https://facebook.github.io/create-react-app/docs/advanced-configuration)
### Deployment
This section has moved here: [https://facebook.github.io/create-react-app/docs/deployment](https://facebook.github.io/create-react-app/docs/deployment)
### `npm run build` fails to minify
This section has moved here: [https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify](https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify)
| Hey! I finally finished recreating this Netflix clone (took me more time than I expected 😅). My idea was to make everything static (movies, series, tv shows, ...) but then I found this really cool TMDB API which you can pull most popular movies, top-rated shows, what's trending, collections, lists, and much more. Really worth checking the effort… | firebase,javascript,react,react-native,react-router,tmdb | 2024-04-07T01:35:22Z | 2024-02-09T23:06:05Z | null | 1 | 0 | 45 | 0 | 0 | 6 | null | null | JavaScript |
HeyFang/parkez | main | # Hello, Parkez is online parking reservation website templete...(incomplete)
site doesnt have any configured db for recording selected spots into db...
i am completely new to backend programming, n somehow tricked my teacher into believing this site works :P
but now i do want to complete it. :)
You guys can help me complete it, all you need to know are basics of front end, php and mysql.
# Running it locally.
1. you will need to install XAMPP server: https://www.apachefriends.org/
2. clone this repo in xampp/htdocs directory.
3. run xampp, start apace server and mysql db.
4. type localhost in your browser and hit enter.
5. you can visit site by typing path of homepage: parkez/login-register/welcome.html
6. you can open myphp admin for configuring databse: <br>
a.create a new db named "login_register" <br>
b.table name "users" <br>
c.create 4 columns, named "id" (int) with idex as primary, "full_name" (varchar), "email" (varchar), "password"
(varchar)... set lengths according to you... <br>
d.hit save and you are good to go :)
| a online parking booking website. | parking,php,educative,learn,helpers,newbie-code,webdev,website,collaborate,css | 2024-03-19T14:38:43Z | 2024-05-09T06:19:27Z | 2024-04-01T16:25:26Z | 2 | 3 | 19 | 0 | 2 | 5 | null | MIT | PHP |
Picovoice/picollm | main | # picoLLM Inference Engine
[](https://github.com/Picovoice/picollm/)
[](https://repo1.maven.org/maven2/ai/picovoice/picollm-android/)
[](https://www.npmjs.com/package/@picovoice/picollm-web)
[](https://cocoapods.org/pods/picoLLM-iOS)<!-- markdown-link-check-disable-line -->
[](https://pypi.org/project/picollm/)
Made in Vancouver, Canada by [Picovoice](https://picovoice.ai)
[](https://twitter.com/AiPicovoice)<!-- markdown-link-check-disable-line -->
[](https://www.youtube.com/channel/UCAdi9sTCXLosG1XeqDwLx7w)
picoLLM Inference Engine is a highly accurate and cross-platform SDK optimized for running compressed large language
models. picoLLM Inference Engine is:
- Accurate; picoLLM Compression improves GPTQ by up to 98%.
- Private; LLM inference runs 100% locally.
- Cross-Platform
- Linux (x86_64), macOS (arm64, x86_64), and Windows (x86_64)
- Raspberry Pi (5 and 4)
- Android and iOS
- Chrome, Safari, Edge, and Firefox
- Runs on CPU and GPU
- Free for open-weight models
## Table of Contents
- [picoLLM](#picollm-inference-engine)
- [Table of Contents](#table-of-contents)
- [Models](#models)
- [AccessKey](#accesskey)
- [Demos](#demos)
- [Python](#python-demos)
- [Node.js](#nodejs-demos)
- [Android](#android-demos)
- [iOS](#ios-demos)
- [Web](#web-demos)
- [C](#c-demos)
- [SDKs](#sdks)
- [Python](#python-sdk)
- [Node.js](#nodejs-sdk)
- [Android](#android-sdk)
- [iOS](#ios-sdk)
- [Web](#web-sdk)
- [C](#c-sdk)
- [Releases](#releases)
- [FAQ](#faq)
## Models
picoLLM Inference Engine supports the following open-weight models. The models are on
[Picovoice Console](https://console.picovoice.ai/).
- Gemma
- `gemma-2b`
- `gemma-2b-it`
- `gemma-7b`
- `gemma-7b-it`
- Llama-2
- `llama-2-7b`
- `llama-2-7b-chat`
- `llama-2-13b`
- `llama-2-13b-chat`
- `llama-2-70b`
- `llama-2-70b-chat`
- Llama-3
- `llama-3-8b`
- `llama-3-8b-instruct`
- `llama-3-70b`
- `llama-3-70b-instruct`
- Mistral
- `mistral-7b-v0.1`
- `mistral-7b-instruct-v0.1`
- `mistral-7b-instruct-v0.2`
- Mixtral
- `mixtral-8x7b-v0.1`
- `mixtral-8x7b-instruct-v0.1`
- Phi-2
- `phi2`
## AccessKey
AccessKey is your authentication and authorization token for deploying Picovoice SDKs, including picoLLM. Anyone who is
using Picovoice needs to have a valid AccessKey. You must keep your AccessKey secret. You would need internet
connectivity to validate your AccessKey with Picovoice license servers even though the LLM inference is running 100%
offline and completely free for open-weight models. Everyone who signs up for
[Picovoice Console](https://console.picovoice.ai/) receives a unique AccessKey.
## Demos
### Python Demos
Install the demo package:
```console
pip3 install picollmdemo
```
Run the following in the terminal:
```console
picollm_demo_completion --access_key ${ACCESS_KEY} --model_path ${MODEL_PATH} --prompt ${PROMPT}
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` with the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` with a prompt string.
For more information about Python demos go to [demo/python](demo/python/README.md).
### Node.js Demos
Install the demo package:
```console
yarn global add @picovoice/picollm-node-demo
```
Run the following in the terminal:
```console
picollm-completion-demo --access_key ${ACCESS_KEY} --model_path ${MODEL_PATH} --prompt ${PROMPT}
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` with the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` with a prompt string.
For more information about Node.js demos go to [demo/nodejs](./demo/nodejs).
### Android Demos
Using Android Studio, open the [Completion demo](demo/android/Completion/) as an Android project, copy your AccessKey into MainActivity.java, and run the application.
To learn about how to use picoLLM in a chat application, try out the [Chat demo](demo/android/Chat/).
For more information about Android demos go to [demo/android](demo/android/README.md).
### iOS Demos
To run the completion demo, go to [demo/ios/Completion](demo/ios/Completion) and run:
```console
pod install
```
Replace `let ACCESS_KEY = "${YOUR_ACCESS_KEY_HERE}"` in the file [VieModel.swift](demo/ios/Completion/PicoLLMCompletionDemo/ViewModel.swift) with your AccessKey obtained from [Picovoice Console](https://console.picovoice.ai/).
Then, using [Xcode](https://developer.apple.com/xcode/), open the generated `PicoLLMCompletionDemo.xcworkspace` and run the application.
To learn about how to use picoLLM in a chat application, try out the [Chat demo](demo/ios/Chat).
For more information about iOS demos go to [demo/ios](demo/ios/README.md).
### Web Demos
From [demo/web](demo/web) run the following in the terminal:
```console
yarn
yarn start
```
(or)
```console
npm install
npm run start
```
Open `http://localhost:5000` in your browser to try the demo.
### C Demos
Build the demo:
```console
cmake -S demo/c/ -B demo/c/build && cmake --build demo/c/build
```
Run the demo:
```console
./demo/c/build/picollm_demo_completion -a ${ACCESS_KEY} -l ${LIBRARY_PATH} -m ${MODEL_FILE_PATH} -p ${PROMPT}
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${LIBRARY_PATH}` with the path to the shared
library file located in the [lib](lib) directory, `${MODEL_FILE_PATH}` with the path to a model file downloaded from
Picovoice Console, and `${PROMPT}` with a prompt string.
For more information about C demos go to [demo/c](demo/c/README.md).
## SDKs
### Python SDK
Install the Python SDK:
```console
pip3 install picollm
```
Create an instance of the engine and generate a prompt completion:
```python
import picollm
pllm = picollm.create(
access_key='${ACCESS_KEY}',
model_path='${MODEL_PATH}')
res = pllm.generate('${PROMPT}')
print(res.completion)
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` to the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` to a prompt string. Finally, when done be sure to explicitly release
the resources using `pllm.release()`.
### Node.js SDK
Install the Node.js SDK:
```console
yarn add @picovoice/picollm-node
```
Create instances of the picoLLM class:
```javascript
const PicoLLM = require("@picovoice/picollm-node");
const pllm = new PicoLLM('${ACCESS_KEY}', '${MODEL_PATH}');
const res = pllm.generate('${PROMPT}');
console.log(res.completion);
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` to the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` to a prompt string. Finally, when done be sure to explicitly release
the resources using `pllm.release()`.
### Android SDK
Create an instance of the inference engine and generate a prompt completion:
```java
import ai.picovoice.picollm.*;
try {
PicoLLM picollm = new PicoLLM.Builder()
.setAccessKey("${ACCESS_KEY}")
.setModelPath("${MODEL_PATH}")
.build();
PicoLLMCompletion res = picollm.generate(
"${PROMPT}",
new PicoLLMGenerateParams.Builder().build());
} catch (PicoLLMException e) { }
```
Replace `${ACCESS_KEY}` with your `AccessKey` from Picovoice Console, `${MODEL_PATH}` to the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` to a prompt string. Finally, when done be sure to explicitly release
the resources using `picollm.delete()`.
### iOS SDK
Create an instance of the engine and generate a prompt completion:
```swift
import PicoLLM
let pllm = try PicoLLM(
accessKey: "${ACCESS_KEY}",
modelPath: "${MODEL_PATH}")
let res = pllm.generate(prompt: "${PROMPT}")
print(res.completion)
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` to the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` to a prompt string.
### Web SDK
Install the web SDK using yarn:
```console
yarn add @picovoice/picollm-web
```
or using npm:
```console
npm install --save @picovoice/picollm-web
```
Create an instance of the engine using `PicoLLMWorker` and transcribe an audio file:
```typescript
import { PicoLLMWorker } from "@picovoice/picollm-web";
const picoLLMModel = {
modelFile: '${MODEL_FILE}'
}
const picoLLM = await PicoLLMWorker.create(
"${ACCESS_KEY}",
picoLLMModel
);
const res = await picoLLM.generate(`${PROMPT}`);
console.log(res.completion);
```
Replace `${ACCESS_KEY}` with yours obtained from [Picovoice Console](https://console.picovoice.ai/), `${MODEL_FILE}` with the contents of the model file as `File`, `Blob` or `URL (path to model file)` format and `${PROMPT}` with a prompt string. Finally, when done release the resources using `picoLLM.release()`.
### C SDK
Create an instance of the engine and generate a prompt completion:
```c
pv_picollm_t *pllm = NULL;
pv_picollm_init(
"${ACCESS_KEY}",
"${MODEL_PATH}",
"best",
&pllm);
pv_picollm_usage_t usage;
pv_picollm_endpoint_t endpoint;
int32_t num_completion_tokens;
pv_picollm_completion_token_t *completion_tokens;
char *output;
pv_picollm_generate(
pllm,
"${PROMPT}",
-1, // completion_token_limit
NULL, // stop_phrases
0, // num_stop_phrases
-1, // seed
0.f, // presence_penalty
0.f, // frequency_penalty
0.f, // temperature
1.f, // top_p
0, // num_top_choices
NULL, // stream_callback
NULL, // stream_callback_context
&usage,
&endpoint,
&completion_tokens,
&num_completion_tokens,
&output);
printf("%s\n", output);
```
Replace `${ACCESS_KEY}` with yours obtained from Picovoice Console, `${MODEL_PATH}` to the path to a model file
downloaded from Picovoice Console, and `${PROMPT}` to a prompt string.
Finally, when done, be sure to release the resources explicitly:
```c
pv_picollm_delete(pllm);
```
## Releases
## FAQ
| On-device LLM inference powered by x-bit quantization | android,ios,javascript,large-language-models,llm,llm-inference,local-llama,local-llm,nodejs,on-device | 2024-04-09T21:23:22Z | 2024-05-22T16:49:03Z | null | 6 | 21 | 12 | 0 | 0 | 5 | null | Apache-2.0 | TypeScript |
Sourish-Kanna/Xplore-Travels-website | main | null | Travel Agency website made for second year mini project | css,html,html-css-javascript,javascript,python-flask,python-flask-application,website,mini-project,travel-website | 2024-04-11T16:22:17Z | 2024-04-30T05:33:28Z | null | 2 | 1 | 11 | 0 | 0 | 5 | null | null | Python |
AJ1904/poemdle-app | main | # POEMDLE
In a world where words weave magic and poetry paints pictures, welcome to Poemdle - where the art of guessing meets the beauty of verse. Instead of guessing just one word, you unravel the mysteries of entire poems. Welcome to a new dimension of wordplay, where every guess is a step closer to unlocking the poet's heart.
## Video
Try it live at [Poemdle](https://poemdle.netlify.app/)
https://github.com/AJ1904/poemdle-app/assets/49027490/bd43ef0b-9fda-4b13-b953-c4ee13e8fc73
Watch on [YouTube](https://www.youtube.com/watch?v=mVsnmNy7WAc)
## Technology Stack
- MindsDB
- Flagsmith
- React
- Javacript
- Python
- CSS
## What will you need to run the app locally
- MindsDB setup locally or access to cloud MindsDB.
- Flagsmith account.
- OpenAI API key.
## Steps to reproduce
1. Clone the Repository:
`git clone https://github.com/aj1904/poemdle-app.git`
2. Navigate to the Project Directory:
`cd poemdle-app`
3. Install Dependencies:
`npm install`
4. Setup [MindsDB](https://mindsdb.com/) account, database and model
- Run the SQL queries present in MindsDBSQLSetup.sql.
- Use your [OpenAI API key](https://openai.com/blog/openai-api).
5. Setup [Flagsmith](https://www.flagsmith.com/) account
- Use your Flagsmith environment id in index.js file.
- Define these flags in your Flagsmith account:
- footer: this determines whether to show footer or not.
- help_popup: this determines whether to show help instructions or not (Work in progress).
- hints: this determines whether to enable hints or not.
- score_tracking: this determines whether to track scores or not.
6. Setup Backend (Optional)
- Not required necessarily, the app works without it.
- But if you want to try your hands on new poems everyday, you can use this python script to connect to your MindsDB database and generate a new poem which will get updated in `poemtoday.js` file.
- Pass a topic name to generate a poem of your wish. `python backend.py 'love'`
- You also have an option to save generated poems in MongoDB database for future reference.
7. Run the Application:
`npm start`
- Navigate to https://localhost:3000 and have fun!
- Or try it live at [Poemdle](https://poemdle.netlify.app/)
| This project is an extension of Wordle and uses AI, MindsDB, Flagsmith and React. | artificial-intelligence,css,flagsmith,javascript,mindsdb,openai-api,python,react | 2024-04-08T00:56:43Z | 2024-04-08T02:06:05Z | null | 1 | 0 | 3 | 0 | 1 | 5 | null | MIT | JavaScript |
tacosontitan/Hazel.js | main | # 💃 Hazel.js
Let's decide once and for all which language is the best; open a PR and cast your vote!
## 💁♀️ Getting Started
Get started by reviewing the answers to the following questions:
- [How do I report security concerns?](./SECURITY.md)
- [How should I behave here?](./CODE_OF_CONDUCT.md)
- [How can I help?](./CONTRIBUTING.md)
Afterward, (assuming you've already cloned the project) you can run the following commands to get started:
```bash
npm i
npm start
```
## 🦄 Voting
You can add your vote to the [`votes.json`](./data/votes.json) file using the format:
```json
{ "language": "csharp", "reason": "C# is better than JavaScript." }
```
### 🐲 Languages
Languages are defined in the [`languages.json`](./data/languages.json) file. If you want to add a new language, you can do so by adding an entry in the following format:
```json
{
"name": "csharp",
"displayName": "C#",
"logo": "https://upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Logo_C_sharp.svg/1820px-Logo_C_sharp.svg.png"
}
```
<sub>**Note:** The `logo` field is optional.</sub>
## 👾 The Battlegrounds
Keep it clean, keep it professional. Other than that, anything goes, as long as it's legal.
 | Vote on your favorite programming language by opening a PR. | battlegrounds,csharp,dotnet,javascript,nodejs,warzone,best-language,languages,voting | 2024-04-25T14:16:09Z | 2024-05-16T23:23:33Z | null | 3 | 3 | 33 | 1 | 2 | 5 | null | MIT | JavaScript |
AsadiAhmad/Online-Shop | main | # Online-Shop
An online shop with user comments
## Tech :hammer_and_wrench: Languages and Tools :
<div>
<img src="https://github.com/devicons/devicon/blob/master/icons/html5/html5-original.svg" title="HTML5" alt="HTML" width="40" height="40"/>
<img src="https://github.com/devicons/devicon/blob/master/icons/css3/css3-plain.svg" title="CSS3" alt="CSS" width="40" height="40"/>
<img src="https://github.com/devicons/devicon/blob/master/icons/javascript/javascript-original.svg" title="Javascript" alt="JS" width="40" height="40"/>
<img src="https://github.com/devicons/devicon/blob/master/icons/jquery/jquery-original-wordmark.svg" title="JQuery" alt="JQuery" width="40" height="40"/>
<img src="https://github.com/devicons/devicon/blob/master/icons/nodejs/nodejs-original-wordmark.svg" title="Nodejs" alt="nodejs" width="40" height="40"/>
<img src="https://github.com/devicons/devicon/blob/master/icons/mongodb/mongodb-original.svg" title="MongoDB" alt="MongoDB" width="40" height="40"/>
</div>
## Tutorial
### Step1 : Install Nodejs
Online Shop uses Nodejs as Backend Language
Download and install Nodejs with this link :
```sh[
https://nodejs.org/en/download
```
### Step2 : Install MongoDB
Online Shop uses MongoDB so install MongoDB
```sh
https://www.mongodb.com/docs/manual/installation/
```
### Step3 : Clone GitHub Repo
Goto your IDE (I usually use Vscode and Webstorm) and clone the src
```sh
https://github.com/AsadiAhmad/Online-Shop.git
```
### Step4 : set your Nodejs Application
the src does'nt have any Nodejs configuration file
create New file named `package.json` in root of src with this lines :
```sh
{
"name": "untitled",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"ejs": "^3.1.9",
"express": "^4.19.2",
"jquery": "^3.7.1",
"jsonwebtoken": "^9.0.2",
"mongodb": "^6.5.0",
"mongoose": "^8.3.0",
"multer": "^1.4.5-lts.1",
"path": "^0.12.7"
}
}
```
Goto your IDE terminall and type
```sh
npm install
```
with this command nodejs will install package-lock.json and set the configurations
### Step5 : Install necessary Packages
Install all of the Packages with npm command
```sh
npm install ejs
```
```sh
npm install express
```
```sh
npm install jquery
```
```sh
npm install jsonwebtoken
```
```sh
npm install mongodb
```
```sh
npm install mongoose
```
```sh
npm install multer
```
```sh
npm install path
```
for checking installed packages you can run this command :
```sh
npm list
```
### Step6 : Create Connection to MongoDB
I have gitignore my connection so you need create new connection file :
Create a Floder named `Connection` in /root/public/JS/BackEnd path
Create js file named `connection.js` like this :
```sh
const { MongoClient } = require('mongodb');
const uri = 'mongodb+srv://<user>:<password>@cluster-0-130.81jyjqx.mongodb.net/';
const dbName = 'OnlineShop';
let db;
async function connection() {
if (!db) {
const client = new MongoClient(uri, { useUnifiedTopology: true });
await client.connect();
db = client.db(dbName);
}
return db;
}
module.exports = connection;
```
#### Dont forget to replcae your `username` and `password` of your Mongo database here
if you have another formate of connection string you can replace it into uri
### Step7 : Create MongoDB Datbase and collections :
create datbase named `OnlineShop`
commands used in MongoDB shell :
```sh
use OnlineShop
```
and Create these three collections :
```sh
use OnlineShop
db.createCollection("Comments")
db.createCollection("Products")
db.createCollection("users")
```
### Step8 : Run the project :
Goto root path run this:
```sh
npm app.js
```
## View
<img src="screenShots/Screenshot (796).png"/>
<img src="screenShots/Screenshot (797).png"/>
<img src="screenShots/Screenshot (798).png"/>
<img src="screenShots/Screenshot (799).png"/>
<img src="screenShots/Screenshot (800).png"/>
<img src="screenShots/Screenshot (801).png"/>
<img src="screenShots/Screenshot (802).png"/>
<img src="screenShots/Screenshot (803).png"/>
<img src="screenShots/Screenshot (804).png"/>
<img src="screenShots/Screenshot (833).png"/>
<img src="screenShots/Screenshot (834).png"/>
<img src="screenShots/Screenshot (835).png"/>
<img src="screenShots/Screenshot (836).png"/>
<img src="screenShots/Screenshot (837).png"/>
<img src="screenShots/Screenshot (838).png"/>
| An online shop with user comments with Nodejs And MongoDB | backend,css,front-end,full-stack,html,javascript,mongodb,nodejs,online-shop,responsive-design | 2024-04-03T20:34:04Z | 2024-05-22T14:08:53Z | null | 1 | 0 | 93 | 0 | 0 | 5 | null | MIT | JavaScript |
warioddly/heritage | main | ## HERITAGE
This is a project that shows the family tree of the [Kyrgyz](https://ru.wikipedia.org/wiki/%D0%9A%D0%B8%D1%80%D0%B3%D0%B8%D0%B7%D1%8B) people. And you can see yourself and search for yourself (if you are Kyrgyz, of course) in the tree.
## How to contribute
If you want to contribute to the project, you can do the following:
- Add yourself and your fathers
- Fix some bugs on the site
- To give ideas for improving the site
- Report any wrong paths in the family tree
- Etc.
The best way to contribute is to fork the project and make a pull request. If you have any questions, you can write to me on [Telegram](https://t.me/warioddly).
## What You must know before contributing
The project is written in Next.js and if you want to contribute, you must know the following:
- History of the Kyrgyz people
- The family tree of your family if you add yourself
- [Learn Next.js](https://nextjs.org/learn) - an interactive Next.js tutorial.
- [Learn React](https://reactjs.org/tutorial/tutorial.html) - an interactive React tutorial.
- [Learn TypeScript](https://www.typescriptlang.org/docs/handbook/intro.html) - an interactive TypeScript tutorial.
- [Learn Tailwind CSS](https://tailwindcss.com/docs) - an interactive Tailwind CSS tutorial.
And it is not necessary to know the technology above, you can write your ideas, etc. (read the section [How to contribute](#how-to-contribute)).
## How to run the project
First, run the development server:
```bash
npm run dev
# or
yarn dev
# or
pnpm dev
# or
bun dev
```
Open [http://localhost:3000](http://localhost:3000) with your browser to see the result.
Wish you a good contribution! 🚀
| The family tree of the Kyrgyz people (Генеалогическое древо кыргызов)🌳 | binary-tree,family-tree,genetics,javascript,js,nextjs,react,reactjs,tree,typescript | 2024-04-29T10:50:33Z | 2024-05-14T17:37:44Z | null | 1 | 4 | 52 | 0 | 1 | 5 | null | null | TypeScript |
vaskovicdejan/RentA-Car-FrontEnd-Angular | master |
[](https://www.linkedin.com/in/samet-kaya-736604170/)
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
# RentACarFrontEnd
This project was generated with [Angular CLI](https://github.com/angular/angular-cli) version 11.2.4.
## Development server
Run `ng serve` for a dev server. Navigate to `http://localhost:4200/`. The app will automatically reload if you change any of the source files.
## Code scaffolding
Run `ng generate component component-name` to generate a new component. You can also use `ng generate directive|pipe|service|class|guard|interface|enum|module`.
## Build
Run `ng build` to build the project. The build artifacts will be stored in the `dist/` directory. Use the `--prod` flag for a production build.
## Running unit tests
Run `ng test` to execute the unit tests via [Karma](https://karma-runner.github.io).
## Running end-to-end tests
Run `ng e2e` to execute the end-to-end tests via [Protractor](http://www.protractortest.org/).
## Further help
To get more help on the Angular CLI use `ng help` or go check out the [Angular CLI Overview and Command Reference](https://angular.io/cli) page.
| RentA-Car-FrontEnd-Angular is an Angular-based front-end project for a car rental service, enabling users to browse cars, view details, and make reservations. | angular,angular-project,javascript,typescript | 2024-04-18T21:44:33Z | 2024-02-11T18:54:12Z | null | 1 | 0 | 32 | 0 | 0 | 5 | null | null | HTML |
VanishMax/foton | main | <p align="center">
<a href="https://foton.sh" target="_blank">
<img src="https://raw.githubusercontent.com/vanishmax/foton/main/apps/docs/public/logo.png" alt="Foton Logo" width="64" height="64">
</a>
</p>
<h1 style="margin-top: 0">Foton</h1>
_⚡ Create TON dApps with the speed of a photon_
> Warning: This project is under active development and is not ready for production use. Each release might and probably will contain breaking changes. If you find bugs when using it, please submit an issue.
[Foton](https://foton.sh) is a TypeScript toolkit for interacting with TON wallets and blockchain as a whole. The library wraps existing solutions into one comfortable API. It supports:
- ✅ Wallet connection
- ✅ Sending transactions
- ✅ Querying the blockchain
- ✅ Deploying and interacting with smart contracts
- ✅ Blueprint and TON Connect integration for easy code migrations
- ✅ Type safe interfaces with full auto-completion for contract methods and returns
Not sure where to start?
- Explore [Foton documentation](https://foton.sh/docs)
- Try building a simple Counter dApp with React and Foton by following [the tutorial](https://foton.sh/docs/guides/tutorial).
- Ask for help or share your feedback in the [Telegram chat](https://t.me/fotonjs)
- Look for a ways to [contribute or donate](https://foton.sh/docs/contribution-and-donation) to the project
## License
The source code is licensed under the terms of [MIT License](./LICENSE). 2024, Max Korsunov.
| ⚡ Create TON dApps with the speed of a foton | blockchain,dapp,javascript,theopennetwork,ton,typescript,web3 | 2024-04-01T17:51:29Z | 2024-05-15T08:26:39Z | 2024-05-13T19:34:03Z | 2 | 0 | 62 | 0 | 0 | 5 | null | MIT | TypeScript |
uigilob/UI | main | <p align="center">
<a href="https://ui-gilob.in">
<img width="20%" src="http://ui.gilob.in/@asset/logo.svg" alt="ui-gilob" />
<h1 align="center">UI-Gilob</h1>
</a>
</p>
</br>
# CDN
```html
<link href="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.css" rel="stylesheet" type="text/css">
<script src="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.js"></script>
```
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>smaple</title> <!-- defulat scropts-->
<link href="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.css" rel="stylesheet" type="text/css">
<script src="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.js"></script>
</head>
<body>
<div class="h1 t-center">Hello World</div>
<script>
$alert("Hello World")
</script>
</body>
</html>
```
## dynamic-load
```html
<div
htp-get="/hello.html"
htp-load="[event]"
htp-t="[target]"
htp-swap="[swap-method]">
</div>
```
```html
<div class="target"
htp-get="/hello.html"
htp-swap="append"
htp-sync="true"
htp-load="click">
Click show button to load Content
</div>
```
## dropdown
```html
<button class="dropdown" d-event="click" data="post-id-2" d-defind="rest" dropdown="trigger">rest</button>
<ul class="dropdown-menu" overflow-x="nowrap" d-event="mouseover" d-defind="rest">
<a href="#home">Home</a>
<a>About</a>
<a disabled>Services</a> <!-- Target disabled: This item is disabled and cannot be clicked. -->
<a event="remove">Contact</a>
<!-- Not closeable when clicked: This item will not close the dropdown when clicked. -->
<button event="remove">Button</button>
</ul>
```
## $http GET
```js
var req = $http.get('/data', { param1: 'value1', param2: 'value2' });
req.done(function(response) {
console.log('GET request successful:', response);
}).error(function() {
console.log('Error occurred during the GET request.');
});
```
## Theme
<ul>
<a href="https://ui.gilob.in/theme/css/" class='h2 bold' style='padding:30px;padding-left:0'>Css</a>
<ul>
<li><a href='https://ui.gilob.in/theme/css/divider/'>Divider</a></li>
<li><a href='https://ui.gilob.in/theme/css/icon/'>Icon</a></li>
</ul>
<li><a href='https://ui.gilob.in/theme/dark/'>Dark</a></li>
<li><a href='https://ui.gilob.in/theme/rules/'>Rules</a></li>
<li><a href='https://ui.gilob.in/theme/switcher/'>Switcher</a></li>
<li><a href='https://ui.gilob.in/theme/variables/'>Variables</a></li>
</ul>
## Ajax
<ul>
<li><a href='https://ui.gilob.in/ajax/$htp/'>$Htp</a></li>
<li><a href='https://ui.gilob.in/ajax/$http/'>$Http</a></li>
<li><a href='https://ui.gilob.in/ajax/dynamic/'>Dynamic</a></li>
</ul>
## components
<ul>
<li><a href='https://ui.gilob.in/components/alert/'>Alert</a></li>
<li><a href='https://ui.gilob.in/components/avatar/'>Avatar</a></li>
<li><a href='https://ui.gilob.in/components/breadcrumbs/'>Breadcrumbs</a></li>
<li><a href='https://ui.gilob.in/components/button/'>Button</a></li>
<li><a href='https://ui.gilob.in/components/carousel/'>Carousel</a></li>
<li><a href='https://ui.gilob.in/components/clipboard/'>Clipboard</a></li>
<li><a href='https://ui.gilob.in/components/collapsible/'>Collapsible</a></li>
<li><a href='https://ui.gilob.in/components/dialog/'>Dialog</a></li>
<li><a href='https://ui.gilob.in/components/dropdown/'>Dropdown</a></li>
<div class='h2 bold' style='padding:30px;padding-left:0'>Form</div>
<ul>
<li><a href='https://ui.gilob.in/components/form/checkbox/'>Checkbox</a></li>
<li><a href='https://ui.gilob.in/components/form/input/'>Input</a></li>
<li><a href='https://ui.gilob.in/components/form/radio/'>Radio</a></li>
<li><a href='https://ui.gilob.in/components/form/select/'>Select</a></li>
<li><a href='https://ui.gilob.in/components/form/textarea/'>Textarea</a></li>
</ul>
<li><a href='https://ui.gilob.in/components/image/'>Image</a></li>
<li><a href='https://ui.gilob.in/components/loader/'>Loader</a></li>
<li><a href='https://ui.gilob.in/components/pagination/'>Pagination</a></li>
<li><a href='https://ui.gilob.in/components/pop-title/'>Pop Title</a></li>
<li><a href='https://ui.gilob.in/components/table/'>Table</a></li>
<li><a href='https://ui.gilob.in/components/tabs/'>Tabs</a></li>
<li><a href='https://ui.gilob.in/components/tabstack/'>Tabstack</a></li>
</ul>
## functions
<ul>
<li><a href='https://ui.gilob.in/functions/cmd/'>Cmd</a></li>
<li><a href='https://ui.gilob.in/functions/device/'>Device</a></li>
<li><a href='https://ui.gilob.in/functions/parserHTML/'>Parserhtml</a></li>
<li><a href='https://ui.gilob.in/functions/reactFrom/'>Reactfrom</a></li>
<li><a href='https://ui.gilob.in/functions/visibility/'>Visibility</a></li>
</ul>
## events
<ul>
<li><a href='https://ui.gilob.in/events/bind/'>Bind</a></li>
<li><a href='https://ui.gilob.in/events/cmd/'>Cmd</a></li>
</ul>
## [template](https://ui.gilob.in/template/)
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>smaple</title>
<link href="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.css" rel="stylesheet" type="text/css">
<script src="https://cdn.jsdelivr.net/gh/uigilob/UI@main/src/ui-gilob.js"></script>
</head>
<body class="theme fixed p0 over-x-adjust center">
<!-- Sidebar -->
<nav class="sidebar b-right" s-defind="menu">
<!-- Sidebar Header -->
<div class="padding-cnt bar-exp">Sidebar Header</div>
<!-- Sidebar Content -->
<div class="sidebar-content flex flex-col gap-l-f padding-cnt">
Sidebar Content
</div>
<!-- Sidebar Footer -->
<div class="padding-cnt" cnt-tag="footer">Sidebar Footer</div>
</nav>
<!-- Main Content Body -->
<div class="body flex flex-col">
<!-- Header -->
<header class=" center-tb b-b p gap" md-fix="true">
<a href="/" class="h6 bold c-p ">BRAND</a>
<button class="button m-auto-l" sidebar="trigger" s-defind="menu">Menu</button>
</header>
<!-- Content Area -->
<div class="home padding-cnt d-scroll">
<h1 class="h1 t-center">Heading of a Blog Post</h1>
<!-- Add your main content here -->
</div>
</div>
<!-- Add your scripts or other body elements here -->
</body>
</html>
```
# Getting Started
Visit [https://ui.gilob.in/get-started](https://ui.gilob.in/get-started) to get started with UI-Gilob.
# CH-Py modules
```html
<link href="https://cdn.gilob.in/v1/import.css?c=all&g=t&f=all" rel="stylesheet" type="text/css">
<script src="https://cdn.gilob.in/v1/import.js?c=all&g=t&g=hl&f=all"></script>
```
```html
<!-- Import all modules -->
<link href="/import.css?c=all" rel="stylesheet" type="text/css">
<script src="/import.js?c=all&g=cmd"></script>
<!-- Or import specific modules -->
<link href="/import.css?c=b&c=at" rel="stylesheet" type="text/css">
<script src="/import.js?c=b&c=at"></script>
```
### Multiple Parts Importing
You can import multiple parts using the following syntax:
```html
<!-- Import multiple parts -->
<link href="/import.css?c=tb" rel="stylesheet" type="text/css">
<script src="/import.js?c=tb"></script>
<!-- Import additional modules -->
<link href="/modules.css?c=b&c=at" rel="stylesheet" type="text/css">
<script src="/import.js?c=b&c=at"></script>
```
## Default Imports
Here's a list of default imports in [Your Web UI Framework/Library Name]:
- `functions` Import functions
- `Ajax` Import Ajax-related modules, including
- `$Http`
- `$htp`
- `theme` theme
## Global
The global table consists of various import keys that allow you to import multiple modules or components at once. Here a breakdown of the available global import keys
| Import Key | Description |
|------------|------------------------------------------------------|
| g=all | Import all modules globals |
| g=e | Event bind |
| g=c | Event cmd |
| g=t | template |
| g=hl | dynamic loading (Ajax) |
## Components
The components table lists the available components in [Your Web UI Framework/Library Name], along with their corresponding import keys and descriptions:
| Component | Import Key | Description |
|--------------|------------|----------------------------------------------------------|
| all | c=all | all Component |
| Alert | c=a | Component for displaying alerts/messages |
| Avatar | c=at | Component for displaying user avatars |
| Breadcrumbs | c=bc | Navigation trail indicating the current page's location |
| Button | c=b | UI button component |
| Clipboard | c=cb | Copy to clipboard functionality |
| Collapsible | c=c | Component for creating collapsible sections |
| Dialog | c=dl | Modal dialog component |
| Dropdown | c=d | Dropdown/select component |
| Image | c=i | Component for displaying images |
| Loader | c=l | Loading indicator component |
| Pagination | c=p | Pagination component for navigating through data |
| Pop Title | c=pt | Popup title component |
| Table | c=t | Table component for displaying tabular data |
| Tabs | c=tb | Tabs component for organizing content |
| Tabstack | c=tk | Tabstack component for organizing multiple tabs |
## Form
| Component | Import Key | Description |
|--------------|------------|--------------------------------------------|
| all | f=all | all input component |
| Checkbox | f=c | Checkbox input component |
| Input | f=i | Text input component |
| Progress | f=p | Progress bar component |
| Radio | f=r | Radio button input component |
| Range | f=rg | Range/slider input component |
| Select | f=s | Select dropdown input component |
| Textarea | f=t | Textarea input component |
| Welcome to Our Web UI-gilob. <Front-end development> 🥴 | ajax,clipboard,compontents,css,form,front-end-development,html,javascript,template,theme | 2024-04-01T17:48:25Z | 2024-05-22T21:51:31Z | 2024-05-15T19:59:35Z | 2 | 0 | 37 | 0 | 2 | 5 | null | Apache-2.0 | JavaScript |
BrennonMeireles/filmaria-react-web | main | # Getting Started with Create React App
This project was bootstrapped with [Create React App](https://github.com/facebook/create-react-app).
## Available Scripts
In the project directory, you can run:
### `npm start`
Runs the app in the development mode.\
Open [http://localhost:3000](http://localhost:3000) to view it in your browser.
The page will reload when you make changes.\
You may also see any lint errors in the console.
### `npm test`
Launches the test runner in the interactive watch mode.\
See the section about [running tests](https://facebook.github.io/create-react-app/docs/running-tests) for more information.
### `npm run build`
Builds the app for production to the `build` folder.\
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.\
Your app is ready to be deployed!
See the section about [deployment](https://facebook.github.io/create-react-app/docs/deployment) for more information.
### `npm run eject`
**Note: this is a one-way operation. Once you `eject`, you can't go back!**
If you aren't satisfied with the build tool and configuration choices, you can `eject` at any time. This command will remove the single build dependency from your project.
Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except `eject` will still work, but they will point to the copied scripts so you can tweak them. At this point you're on your own.
You don't have to ever use `eject`. The curated feature set is suitable for small and middle deployments, and you shouldn't feel obligated to use this feature. However we understand that this tool wouldn't be useful if you couldn't customize it when you are ready for it.
## Learn More
You can learn more in the [Create React App documentation](https://facebook.github.io/create-react-app/docs/getting-started).
To learn React, check out the [React documentation](https://reactjs.org/).
### Code Splitting
This section has moved here: [https://facebook.github.io/create-react-app/docs/code-splitting](https://facebook.github.io/create-react-app/docs/code-splitting)
### Analyzing the Bundle Size
This section has moved here: [https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size](https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size)
### Making a Progressive Web App
This section has moved here: [https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app](https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app)
### Advanced Configuration
This section has moved here: [https://facebook.github.io/create-react-app/docs/advanced-configuration](https://facebook.github.io/create-react-app/docs/advanced-configuration)
### Deployment
This section has moved here: [https://facebook.github.io/create-react-app/docs/deployment](https://facebook.github.io/create-react-app/docs/deployment)
### `npm run build` fails to minify
This section has moved here: [https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify](https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify)
| null | api,css,css3,front-end,frontend,html,html-css,html5,javascript,movies | 2024-04-10T13:04:34Z | 2024-04-15T13:59:10Z | null | 1 | 0 | 5 | 0 | 0 | 5 | null | null | JavaScript |
khadem-mh/form | main |
# <p align="center"> Hi there 👋 I'm Mohammad Hossein 👨💻 </p>
<p align="center"> React Js expert and FrontEnd Developer from Iran.</p>
## Description Project
- Create a beautiful and very useful form on login and register pages and ... React JS.
- Fully optimized and cleanly programmed, and the principle of being a base component in this project is respected.
- This way, you no longer need to validate the server-side validation, which means that you are following the DRY (Don Repeat Yourself) rule.
- This form is very flexible in terms of customization.
>### Languages
>> 
>>
>> 
>>
>> 
>>
>> 
>### Packages
>> 
## View of the project
<img src="./public/FolderShowTemplateProject/vid.gif" width="350px"/>
## Getting Started
Before running the project, it is necessary to install npm on your system, then you can put the following command in the path of the project
and after installing the related packages run the project.
```
> npm install
```
OR
```
> npm i
```
Then, after you finish installing the packages, run this command to start your React program.
```
> npm start
```
### `npm start`
Runs the app in the development mode.\
Open [http://localhost:3000](http://localhost:3000) to view it in your browser.
The page will reload when you make changes.\
You may also see any lint errors in the console.
### Guid
If you are not installed on your system Node.js and Npm, go to this [Link Install](https://nodejs.org/en/download) and install and then proceed to the above steps
Install Node.js and NPM in Windows via Node.js Installer
___
>### Social Network
> [<img src="./public/Images/github.png" width="30">](https://github.com/khadem-mh)
> [<img src="./public/Images/pintrest.png" width="30">](https://pinterest.com/khadem_mh)
> [<img src="./public/Images/telegram.png" width="30">](https://t.me/mhkhadem)
> [<img src="./public/Images/whatsapp.png" width="30">](https://wa.me/989031335939)
> [<img src="./public/Images/wakatimesvg.png" width="130">](https://wakatime.com/@khadem_mh)
| Create a beautiful and very useful form on login and register pages and ... React JS. | componen,css,form,form-component,input-validation,javascript,login,login-forms,login-page,react | 2024-04-10T16:57:16Z | 2024-05-04T13:14:02Z | null | 1 | 0 | 7 | 0 | 2 | 5 | null | MIT | JavaScript |
suryavaddiraju/irctc-api | main | A package built on top of IRCTC Website APIs to book train tickets, managing user profile faster and simpler. Currently this package only works on NodeJs environment and we were not recommending this to use on browser or any other Javascript environment.
[](https://www.npmjs.com/package/irctc-api)
[](https://www.npmjs.com/package/irctc-api)
[](https://github.com/suryavaddiraju/irctc-api/graphs/contributors)
[](http://www.apache.org/licenses/LICENSE-2.0)
[](https://www.npmjs.com/package/irctc-api)
[](https://github.com/suryavaddiraju/irctc-api/issues)
[](https://github.com/suryavaddiraju/irctc-api)
[](https://github.com/suryavaddiraju/irctc-api/actions/workflows/node.js.yml)
> [!NOTE]
> ```
> This irctc-api script for automating IRCTC ticket booking
> is created strictly for educational purposes. The code and its
> usage are intended to showcase irctc-api testing capabilities and
> best practices. Any attempt to use this script for unauthorized
> access or activities that violate IRCTC terms of service or legal
> regulations is strictly prohibited. The author(s) and associated
> entities are not responsible for any misuse or legal consequences
> resulting from the use of this script for any unauthorized
> activities.
> ```
## Useful Links
<a href="https://github.com/suryavaddiraju/irctc-api"><img src="https://github.githubassets.com/assets/GitHub-Mark-ea2971cee799.png" alt="GitHub Logo" width="50" height="50"/></a> <a href="https://www.npmjs.com/package/irctc-api"><img src="https://upload.wikimedia.org/wikipedia/commons/d/db/Npm-logo.svg" alt="npm Logo" width="50" height="50"/></a> <a href="https://dev.vaddiraju.in/irctc-api/api_reference"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Read-the-docs.png/330px-Read-the-docs.png" alt="Documentation Logo" width="50" height="50"/></a>
## Installing
To install the this package, simply type i or install irctc-api using the node package manager
```shell
npm install irctc-api
```
## Prerequisite
This Package uses [viu](https://github.com/atanunq/viu), A rust module uses iterm image protocol for displaying images within System Terminal.
We use that for displaying captcha images on command line for login and bookings as to make your booking flow in a seamless way.
`irctc-api` automatically installs `viu` binary based on your os and processor architecture, If we could not find your viu binary related to your processor and os, you are required to install `viu` through their standard installation.
Then provide `viu` binary path in params as
```json
{
"train_number": "11020",
"viu":"path/to/binary/viu | path/to/binary/viu.exe"
}
```
### Notes
- Currently this project is designed to accept only UPI Collect request as payment option and other payment modes are not supported as of now. When the payment request is initiated, The command line will display the payment request details such that you need to complete the payment from your UPI mobile App.
### Import
This Package exports a class named `IRCTC` which contains three functions.
- book
- last_transaction
- pnr_status
To send a request, you only need to import the `IRCTC`.
```js
// ES5 example
const { IRCTC } = require("irctc-api");
```
```js
// ES6+ example
import { IRCTC } from "irctc-api";
```
### Examples
The Code Examples are hosted at [Github Repo - suryavaddiraju/irctc-api](https://github.com/suryavaddiraju/irctc-api/tree/main/examples)
### Usage
To send a request, you:
- Initiate IRCTC class
- Call available function operation on class with input as javascript object.
```js
// a client can be shared by different commands. But it is currently in development untill then use client seperately.
const client = new IRCTC();
const params = {
// refer https://dev.vaddiraju.in/irctc-api/api_reference#book_input
};
const command = await client.book(params);
```
#### Async/await
We recommend using [await](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await)
operator to wait for the promise returned by send operation as follows:
```js
// async/await.
try {
const data = await client.book(params);
// process data.
} catch (error) {
// error handling.
} finally {
// finally.
}
```
Async-await is clean, concise, intuitive, easy to debug and has better error handling
as compared to using Promise chains or callbacks.
## Getting Help
Please use these community resources for getting help.
We use the [GitHub issues](https://github.com/suryavaddiraju/irctc-api/issues) for tracking bugs and feature requests, but have limited bandwidth to address them.
- Visit [API Reference](https://dev.vaddiraju.in/irctc-api/api_reference).
## Contributing
Any modifications will be overwritten the next time the `irctc-api` package is updated. To contribute to the package you can check our [contribution](https://dev.vaddiraju.in/irctc-api/contribution) page.
## License
This package is distributed under the
[Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0),
see LICENSE for more information.
## Client Commands (Operations List)
<details>
<summary>
book
</summary>
<a href="https://dev.vaddiraju.in/irctc-api/api_reference#book">Command API Reference</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#book_input">Input</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#book_output">Output</a>
</details>
<details>
<summary>
last_transaction
</summary>
<a href="https://dev.vaddiraju.in/irctc-api/api_reference#last_transaction">Command API Reference</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#last_transaction_input">Input</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#last_transaction_output">Output</a>
</details>
<details>
<summary>
pnr_status
</summary>
<a href="https://dev.vaddiraju.in/irctc-api/api_reference#pnr_status">Command API Reference</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#pnr_status_input">Input</a> / <a href="https://dev.vaddiraju.in/irctc-api/api_reference#pnr_status_output">Output</a>
</details>
## Copyright
All Rights Reserved. © Vaddiraju Surya Teja, 2024
| A NodeJS only package built on top of IRCTC Website APIs to book train tickets, managing user profile faster and simpler. | api,booking,cli,command,india,indian,irctc,javascript,node,npm | 2024-04-16T08:17:04Z | 2024-05-14T21:48:14Z | 2024-05-14T21:48:14Z | 1 | 32 | 84 | 0 | 2 | 5 | null | Apache-2.0 | JavaScript |
project-comercio/frontend-project | master | This is a [Next.js](https://nextjs.org/) project bootstrapped with [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app).
## Getting Started
First, run the development server:
```bash
npm run dev
# or
yarn dev
# or
pnpm dev
# or
bun dev
```
Open [http://localhost:3000](http://localhost:3000) with your browser to see the result.
You can start editing the page by modifying `app/page.tsx`. The page auto-updates as you edit the file.
This project uses [`next/font`](https://nextjs.org/docs/basic-features/font-optimization) to automatically optimize and load Inter, a custom Google Font.
## Learn More
To learn more about Next.js, take a look at the following resources:
- [Next.js Documentation](https://nextjs.org/docs) - learn about Next.js features and API.
- [Learn Next.js](https://nextjs.org/learn) - an interactive Next.js tutorial.
You can check out [the Next.js GitHub repository](https://github.com/vercel/next.js/) - your feedback and contributions are welcome!
## Deploy on Vercel
The easiest way to deploy your Next.js app is to use the [Vercel Platform](https://vercel.com/new?utm_medium=default-template&filter=next.js&utm_source=create-next-app&utm_campaign=create-next-app-readme) from the creators of Next.js.
Check out our [Next.js deployment documentation](https://nextjs.org/docs/deployment) for more details.
| Projeto frontend da plataforma do projeto de comércio. Desenvolvido em NextJS, Typescript, Graphql, Tailwind, Clerk e SCSS | javascript,nextjs,react,scss,tailwind,typescript,web-development | 2024-04-06T02:20:17Z | 2024-05-20T19:00:22Z | null | 5 | 26 | 112 | 0 | 2 | 5 | null | null | TypeScript |
SJ22032003/geekster-react-module | main | # Geekster React Module
This repository is a collection of classwork, homework, and revision materials for students learning React at Geekster. It's structured by day and topic, making it easy to navigate and find the resources you need.
## Structure
- `CUSTOM_HOOK/`: Learn how to create and use custom hooks in React.
- `DAY_2_REACT_USING_CDN/`: Learn how to use React with a CDN and create your first components.
- `DAY_3_CRA_N_COMPONENTS/`: Learn how to use Create React App and build a simple application.
- `DAY_4_PROPS/`: Understand how to use props in React.
- `DAY_5_USE_STATE/`: Learn about the useState hook and how to manage state in your components.
- `DAY_6_LIST/`: Understand how to render lists in React.
- `DAY_7_AXIOS/`: Learn how to make HTTP requests in React using Axios.
- `DAY_8_OPTIMIZATION/`: Learn about optimization techniques in React.
- `REVISION/`: Revision materials and interview questions for self-study.
- `PROJECT/`: A project to test your React skills.
## Getting Started
To get started with the materials in this repository, clone it to your local machine, navigate to the directory of the day or topic you're interested in, and follow the instructions in the `README.md` file.
## Contributing
I welcome contributions from students! If you have a resource you'd like to add, or a revision question you think would be useful, please open a pull request.
| This repository is a comprehensive resource for students learning React. It includes classwork, homework, and revision materials, all organized by day and topic for easy navigation. | axios,cdn,custom-hooks,hooks,javascript,optimization,reactjs,revision,self-study | 2024-04-23T17:39:38Z | 2024-05-22T15:34:31Z | null | 1 | 0 | 51 | 0 | 0 | 5 | null | null | JavaScript |
BrennonMeireles/gerador-de-numeros-aleatorios | main |
# contador aleatorio de numeros
| null | css,css3,front-end,frontend,html,html-css-javascript,html5,javascript,js,react | 2024-04-03T13:06:56Z | 2024-04-03T13:45:31Z | null | 1 | 0 | 3 | 0 | 0 | 5 | null | null | JavaScript |
yWorks/yfiles-layout-reactflow | main | # yFiles Layout Algorithms for React Flow
[](https://www.npmjs.org/package/@yworks/yfiles-layout-reactflow)
Welcome to the *yFiles Layout Algorithms for React Flow* module, a powerful and versatile layout add-on for React Flow based on the [yFiles](https://www.yworks.com/yfiles-overview) library.
## Project Layout
This is the parent repository for the *yFiles Layout Algorithms for React Flow* lib containing the following folders:
* [`yfiles-layout-reactflow/`](yfiles-layout-reactflow) - The actual *yFiles Layout Algorithms for React Flow* lib
* [`examples/`](examples) - Testing app for the individual components
* [`doc/`](doc) - Documentation sources and toolchain
## Getting Started
Please refer to the [yfiles-layout-reactflow library README](yfiles-layout-reactflow/README.md) for detailed instructions.
## Running it
1. Run `npm install` on the toplevel repository.
2. Copy a valid [license for yFiles for HTML](https://www.yworks.com/products/yfiles-for-html) in the `examples/src` folder
3. Run `npm run dev`
## Live Playground
[](https://docs.yworks.com/yfiles-layout-reactflow/introduction/welcome)
Try the *yFiles Layout Algorithms for React Flow* directly in your browser with our [playground](https://docs.yworks.com/yfiles-layout-reactflow/introduction/welcome).
## Licensing
All owners of a valid software license for [yFiles for HTML](https://www.yworks.com/products/yfiles-for-html)
are allowed to use these sources as the basis for their own [yFiles for HTML](https://www.yworks.com/products/yfiles-for-html)
powered applications.
Use of such programs is governed by the rights and conditions as set out in the
[yFiles for HTML license agreement](https://www.yworks.com/products/yfiles-for-html/sla).
You can evaluate yFiles for 60 days free of charge on [my.yworks.com](https://my.yworks.com/signup?product=YFILES_HTML_EVAL).
For more information, see the `LICENSE` file.
## Learn More
For detailed instructions on how to use and configure the layout module, please refer to the comprehensive [documentation](https://docs.yworks.com/yfiles-layout-reactflow/introduction/welcome) provided.
For further information about [yFiles for HTML](https://www.yworks.com/yfiles-overview) and our company, please visit [yWorks.com](https://www.yworks.com).
For support or feedback, please reach out to [our support team](https://www.yworks.com/products/yfiles/support) or open an [issue on GitHub](https://github.com/yWorks/yfiles-layout-reactflow/issues). Happy diagramming!
| yFiles Layouts for React Flow - A layout library for React Flow providing powerful yFiles layout algorithms and supporting components | diagram,graph,javascript,layout,library,react,reactflow,typescript,yfiles,xyflow | 2024-04-10T12:15:02Z | 2024-05-16T09:02:16Z | 2024-05-16T09:02:16Z | 18 | 6 | 27 | 0 | 0 | 5 | null | NOASSERTION | TypeScript |
SH20RAJ/QueryX | main | # QueryX
[](https://github.com/SH20RAJ/QueryX/blob/main/LICENSE)
[](https://github.com/SH20RAJ/QueryX/issues)
[](https://github.com/SH20RAJ/QueryX/stargazers)
[](https://github.com/SH20RAJ/QueryX/network)
QueryX is a lightweight JavaScript library that provides a jQuery-like interface for DOM manipulation and traversal. It allows you to select elements, add/remove classes, manipulate attributes, traverse the DOM, and more, similar to jQuery but in a simpler and more lightweight manner.
[Dev.to
](https://dev.to/sh20raj/queryx-a-lightweight-javascript-library-for-dom-manipulation-3hic)
## Features
- **DOM Selection:** Select elements from the DOM using CSS selectors.
- **DOM Manipulation:** Add, remove, and modify elements and their attributes.
- **Event Handling:** Attach and detach event handlers to elements.
- **DOM Traversal:** Traverse the DOM tree with ease.
- **Chaining:** Chain multiple operations together for cleaner code.
## Getting Started
To get started with QueryX, include the `queryX.js` file in your project:
```html
<script src="path/to/queryX.js"></script>
```
Alternatively, you can use a CDN link:
```html
<script src="https://cdn.jsdelivr.net/gh/SH20RAJ/QueryX@main/QueryX.js"></script>
```
or
```html
<script src="https://cdn.jsdelivr.net/npm/queryxjs"></script>
```
## Usage
```javascript
// Example Usage
queryX('button').on('click', function() {
queryX(this).toggleClass('active');
});
queryX('.container').append('<div class="new-element">New Element</div>');
var formData = queryX('form').serialize();
console.log(formData);
queryX('.parent').children().addClass('child-element');
queryX('.element').closest('.container').css('background-color', 'red');
```
## Documentation
For detailed documentation and examples, please refer to the [Documentation](./docs/) section (link to your documentation).
## Contributing
Contributions are welcome! If you have any suggestions, bug reports, or feature requests, please open an issue or submit a pull request.
## License
This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
---
[](https://visitorbadge.io/status?path=https%3A%2F%2Fgithub.com%2FSH20RAJ%2FQueryX%2F)
| QueryX is a lightweight JavaScript library that provides a jQuery-like interface for DOM manipulation and traversal. It allows you to select elements, add/remove classes, manipulate attributes, traverse the DOM, and more, similar to jQuery but in a simpler and more lightweight manner. | dom-manipulation,javascript,jquery,jquery-alternative,sh20raj | 2024-03-31T12:50:15Z | 2024-04-03T12:33:57Z | null | 1 | 0 | 11 | 0 | 1 | 4 | null | MIT | JavaScript |
LZF-fe/AtEditor | master | # AtEditor
react组件，文本输入关键词弹出列表，选中变成标签，删除一块删除，例如微信输入框艾特@
GitHub地址：[https://github.com/LZF-fe/AtEditor](https://github.com/LZF-fe/AtEditor)
npm地址：[https://www.npmjs.com/package/react-at-editor](https://www.npmjs.com/package/react-at-editor)
## 安装和使用
要安装和使用这个项目，你需要按照以下步骤操作：
直接
`npm i react-at-editor`
或者：
1. 克隆或下载项目代码。
2. 在终端中进入项目目录。
3. 运行 `npm install` 来安装依赖项。
4. 运行 `npm run dev` 来启动项目。
## 效果示例
## 使用示例
```
const defaultList = [
{
label: "小李1",
value: "小李1",
},
{
label: "小李2",
value: "小李2",
},
];
function App() {
const atRef = useRef(null)
return (
<div>
<AtEditor
ref={atRef}
trigger='@'
style={{width: '400px'}}
atList={defaultList}
>
</AtEditor>
</div>
)
}
```
## 参数说明
```
/**
*
* @param {React.RefObject} refInstance 组件ref
* @param {Array} atList: 下拉框的选项
* @param {String} trigger: 关键字
* @param {String} placeholder 占位符
* @param {String} className 样式类名
* @param {Object} style 样式style
* @param {Object} showCount 是否显示输入框字符长度、最大长度、是否显示message提示
* @param {Function} onInput 输入框变化时的回调
* @param {Function} replaceNormalToHtml 自定义构造回显格式，普通字符串替换成html字符串
* @returns
*/
const AtEditor = ({
refInstance,
atList = defaultList,
trigger = '@',
placeholder = '请输入',
className = '',
style = {},
showCount = {},
onInput,
replaceNormalToHtml = _replaceNormalToHtml
}) => {
}
```
## 其他说明
### forwardRef+useImperativeHandle向外抛出了这五个方法用于获取和设置输入框的值
```
useImperativeHandle(refInstance, () => {
return {
getNormalData, // 得到输入框显示的字符串，没经过任何包装
getHtmlData, // 得到html字符串
setDataFromNormal, // 把后台拿到的普通字符串赋到输入框，用于回显
setDataFromHtml, // 把html字符串直接值赋到输入框，用于回显
resetData, // 重置输入框
}
}, []);
```
```
export default forwardRef(
(props, ref) => <AtEditor {...props} refInstance={ref} />
)
```
### 在父组件使用：例如atRef.current.getHtmlData()、atRef.current.setDataFromHtml(xxx)
----------------------
### 有用的话点个免费的star谢谢 | react组件，文本输入关键词弹出列表，选中变成标签，删除一块删除，例如微信输入框艾特@ | javascript,react | 2024-04-16T06:02:20Z | 2024-04-29T02:38:06Z | null | 1 | 0 | 9 | 0 | 0 | 4 | null | null | JavaScript |
jxlee007/PROJECT-5-Sundown | main | # PROJECT-5: Sundown
Portfolio Website from Awwwards
## Description
The Sundown Studio portfolio website is a showcase of unique experiences and environments created by a multi-disciplinary design team. The website incorporates modern design elements and interactive features to engage visitors.
## Key Features
- **Navigation and Hero Section:** The navigation bar includes links to different sections like Work, Studio, and Contact. The hero section features a striking tagline "SPACES THAT INSPIRE" and introduces Sundown Studio as a studio focused on creating unique experiences and environments.
- **Interactive Elements and Section Transitions:** Interactive elements like a dot that follows the mouse enhance the user experience. Smooth transitions between sections make navigation seamless and enjoyable.
- **Project Showcase and About Me:** The portfolio showcases various projects with videos, images, and descriptions, highlighting the studio's capabilities. An "About Me" section introduces the team behind Sundown Studio, their design philosophy, and their passion for collaboration and creativity.
- **Subscription Call-to-Action and Footer:** The website encourages visitors to subscribe to the developer's content on YouTube, fostering engagement and community building. The footer includes copyright information, location details, and links to social media profiles for further interaction.
## Technologies Used
- **HTML5:** Markup language for structuring the content.
- **CSS3:** Styling language for layout and presentation.
- **JavaScript:** Used for interactive elements, animations, and functionality.
- **External Libraries:** Utilizes Locomotive Scroll for smooth scrolling and Swiper JS for interactive slideshows.
## Responsive Design
The website is designed to be responsive, ensuring a seamless and enjoyable user experience across various devices. Media queries are employed to adjust styles for small screens.
## How to Use
1. Clone the repository.
2. Open the `index.html` file in a web browser to explore the website.
## Credits
- **Original Website:** [https://www.sundown-studio.com/](https://www.sundown-studio.com/)
- **Locomotive Scroll:** [https://github.com/locomotivemtl/locomotive-scroll](https://github.com/locomotivemtl/locomotive-scroll)
- **Swiper JS:** [https://swiperjs.com/](https://swiperjs.com/)
- **Remixicon:** [https://remixicon.com/](https://remixicon.com/)
## Author
[Jagmohan Singh Malhi](https://www.linkedin.com/in/jagmohan-singh-malhi-a67805243/)
| The Sundown Studio portfolio website, recognized by Awwwards, showcases modern design elements, interactive features like smooth scrolling, and project showcases. Built with HTML5, CSS3, and JavaScript, it offers a responsive experience across devices, supported by external libraries like Locomotive Scroll and Swiper JS. Explore the live website | clone,css3,css3-flexbox,html5,javascript,netlify,responsive-design,webdesign,website,github | 2024-03-29T15:10:45Z | 2024-04-25T07:58:34Z | null | 1 | 0 | 19 | 0 | 1 | 4 | null | null | CSS |
DulangaDasanayake/novamart | main | # [Platinum](novamart.onrender.com) · [](https://github.com/facebook/react/blob/main/LICENSE) [](https://legacy.reactjs.org/docs/how-to-contribute.html#your-first-pull-request)
Remember to give me your generous ⭐ Thanks you so very much !!!
Full-stack E-commerce web application built with the MERN stack(MongoDB,Express,React & Node), Bootstrap, Redux toolkit and hosted on Render.com Browse, shop, and checkout with ease! Stay alert for updates..
<img src="readmedata/home.JPG" alt="Image Description" width="800" height="500">
```javascript
return (
<>
{!keyword ? (
<ProductCarousel />
) : (
<Link to="/" className="btn btn-light mb-4">
Go Back
</Link>
)}
{isLoading ? (
<Loader />
) : error ? (
<Message variant="danger">
{error?.data?.message || error.error}
</Message>
) : (
<>
<h1>Latest Products</h1>
<Row>
{data.products.map((product) => (
<Col key={product._id} sm={12} md={6} lg={4} xl={3}>
<Product product={product} />
</Col>
))}
</Row>
<Paginate
pages={data.pages}
page={data.page}
keyword={keyword ? keyword : ""}
/>
</>
)}
</>
);
};
```
## Table of Contents
- [Features](#features)
- [Used Technologies](#used-technologies)
- [Installation](#installation)
- [Usage](#usage)
- [Contributing](#contributing)
- [License](#license)
### Features
- Full featured shopping cart
- Product reviews and ratings system
- Top products carousel on main page
- Product pagination
- Product search feature
- User profile with orders
- Admin product management
- Admin user management
- Admin Order details page
- Mark orders as delivered option
- Checkout process (shipping, payment method, etc)
- PayPal / credit card integration
- Database seeder (products & users)
<img src="readmedata/product.JPG" alt="Image Description" width="800" height="500">
### Used Technologies
- **Frontend:**
- React.js
- Redux for state management
- React Router for navigation
- Bootstrap for css styling
- **Backend:**
- Node.js
- Express.js for middleware
- Mongoose for object modeling
- JSON Web Tokens (JWT) for authentication
- **Database**
- MongoDB for product & user detail storing.
- **Payment**
- Paypal & Card payment methods are available.
- **Hosting:**
- Render.com for deployment and hosting
- Web App Demo Link:
### Installation
1. **Clone the repository:**
```bash
git clone https://github.com/DulangaDasanayake/novamart.git
```
2. **Navigate to the project directory:**
```bash
cd novamart
```
3. **Install dependencies for both frontend and backend:**
```bash
cd client
npm install
cd ..
npm install
```
4. **Set up environment variables:**
Rename the `.env.example` file in the `root` directory and add the following variables:
Replace `your_mongodb_uri` with your MongoDB connection string and `your_jwt_secret` with a secret key for JWT.
```bash
NODE_ENV = development
PORT = 5000
MONGO_URI = your mongodb uri
JWT_SECRET = your jwt secret key
PAYPAL_CLIENT_ID = your paypal client id
```
### Usage
1. **Start the backend server:**
```bash
cd backend
npm start
```
2. **Start the frontend development server:**
```bash
cd frontend
npm start
```
3. **Start both backend & frontend**
```bash
cd novamart
npm run dev
```
4. **Open your browser and navigate to `http://localhost:3000` to view the application.**
### Contributing
Contributors are warmly welcome! If you'd like to contribute to this project, please follow these steps:
1. Fork the repository.
2. Create a new branch (`git checkout -b feature/new-feature`).
3. Make your changes.
4. Commit your changes (`git commit -am 'Add new feature'`).
5. Push to the branch (`git push origin feature/new-feature`).
6. Create a new Pull Request.
### License
This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
### Thanks Giving ❤️
Thanks for Developers of npm, render.com, paypal, react, node, vs code
vs code extension developers and every each developer that helped me out to finish this project...
| Full-stack E-commerce web app built with the MERN Stack, Bootstrap, Redux toolkit and hosted on Render.com, Stay alert for updates.. | advanced,authentication,mern,redux,fullstack,javascript,mern-shop,shop,proshop,e-commerce | 2024-04-10T06:22:13Z | 2024-05-21T04:15:14Z | null | 1 | 0 | 193 | 0 | 0 | 4 | null | MIT | JavaScript |
leotamminen/Who-wants-to-be-an-engineer | master | # Who Wants to Be an Engineer
## Overview
This is a group project for the University of Turku course "DTEK2074 Information Technology Labs". The project features a quiz game inspired by "Who Wants to Be a Millionaire", with the frontend built using React.
Working version of the game is deployed to Vercel and can be played [here](https://who-wants-to-be-an-engineer.vercel.app/)
Keep in mind that the current version is still under development and there are can be (and are) unhandled errors.
## Project Status
The project is currently at an early stage of development. It consists of two main branches:
- **master**: This branch contains the stable version of the project.
- **dev**: Development work is done on this branch. Changes are made here and then merged into master once they are working properly.
## Project Goal
The primary goal of this project is to create a quiz game using the MERN stack and deploy it to Vercel. The game will be fully functional and feature AI-generated questions. The backup questions are stored in a MongoDB database. These backup questions serve as a fail-safe option in case of any issues with the AI generation process.
## TODO:
Priority:
- [ ] Handle AI generated question error and use backup questions
- [ ] Change the format from earning money to earning cr
- [ ] Lifelines to frontend
- [ ] 50:50
- [ ] Phone a friend
- [ ] Ask the audience
Optional:
- [ ] Scoreboard system (?)
- [ ] About page (?)
- [ ] Language selection EN/FI (?)
- [ ] Dark mode switch (?)
- [ ] Difficulty selection (?)
## Authors
- [Leo](https://github.com/leotamminen), [Jaani](https://github.com/Sodejaa), [Joonas](https://github.com/saljoo)
## License
This project is licensed under the [MIT License](LICENSE).
| Quiz game with AI generated questions | javascript,mern-stack,nodejs,react,mongodb | 2024-03-27T15:56:10Z | 2024-04-08T12:17:17Z | null | 3 | 18 | 20 | 0 | 2 | 4 | null | null | JavaScript |
hey-api/upload-openapi-spec | main | <div align="center">
<img width="150" height="150" src="https://heyapi.vercel.app/logo.png" alt="Logo">
<h1 align="center"><b>Upload OpenAPI Specification</b></h1>
<p align="center">A GitHub Action that uploads your OpenAPI specifications to Hey API 🚀</p>
</div>
To use this action, you have to be registered with
[Hey API](https://heyapi.vercel.app/). If you don't have an account, please
[email us](mailto:lmenus@lmen.us) or
[open an issue](https://github.com/hey-api/upload-openapi-spec/issues) and we
will set you up.
## Usage
Create a new GitHub workflow or add an upload step to your existing workflow
inside your API codebase.
```yaml
name: Upload OpenAPI Specification
on:
push:
branches:
- main
jobs:
upload-openapi-spec:
runs-on: ubuntu-latest
steps:
- name: Checkout
uses: actions/checkout@v4
- name: Upload OpenAPI spec
uses: hey-api/upload-openapi-spec@v1
with:
hey-api-token: ${{ secrets.HEY_API_TOKEN }}
path-to-openapi: path/to/openapi.json
```
The example above will send your OpenAPI spec to Hey API on every push to `main`
branch.
## Inputs
To successfully upload an OpenAPI specification, you need to provide the
following inputs (see `with` in the example above)
### `hey-api-token`
This is the authorization token you obtained from us.
### `path-to-openapi`
A relative path to your OpenAPI spec file within the repository. Note that you
might need an additional step in your GitHub workflow to generate this file (see
[FastAPI example](https://fastapi.tiangolo.com/how-to/extending-openapi/#generate-the-openapi-schema)).
## Next Steps
Please follow the
[integrations guide](https://heyapi.vercel.app/openapi-ts/integrations.html) on
our website for the next steps.
| Upload your OpenAPI specification to Hey API 🚀 | actions,angular,axios,codegen,fetch,github,javascript,nodejs,openapi,swagger | 2024-04-13T18:15:45Z | 2024-04-20T08:03:52Z | 2024-04-20T07:51:46Z | 1 | 8 | 19 | 0 | 0 | 4 | null | null | TypeScript |
codeaashu/Visionary-Architects | main | # Visionary-Architects
A Modern 🚀 Responsive Website Design of Architects Company " Visionary Architects " who achieve mystery in the Architects design & creating environments where innovation meets tradition, and their design transcend imagination...
### 🔸TechStack 👉🏻 HTML - CSS - JavaScript - Bootstrap - Odometer
### 🔸LOC ( line Of Code ) 👉🏻 " HTML - 406 " , " CSS - 8423 " , " JavaScript - 1693 "
### 🔸Design 👉🏻 Figma & Pinterest
# Mockup Design 1 👇🏻
# Mockup Design 2 👇🏻
# Mockup Design 3 👇🏻
# Layout Design 👇🏻
# Layout Design 👇🏻
| Modern Responsive Website Design of Architects Company who achieve mystery in the Architects design & creating environments where innovation meets tradition, and their design transcend imagination... | architecture-design,college-project,css-framework,css-library,css3,frontend-project,github,html-css-javascript,html5,javascript | 2024-03-24T04:09:53Z | 2024-05-03T18:19:16Z | null | 1 | 0 | 109 | 0 | 0 | 4 | null | null | JavaScript |
piyush-eon/react-giphy-clone | master | # Build a GIPHY Clone with React JS and Tailwind CSS
## [Click Here to Watch Full tutorial on Youtube](https://www.youtube.com/watch?v=wtC1_Ea9_wk)
| Build a GIPHY Clone with React JS and Tailwind CSS | javascript,react,reactjs,tailwindcss | 2024-05-01T18:09:23Z | 2024-05-05T04:19:25Z | null | 1 | 0 | 2 | 1 | 2 | 4 | null | null | JavaScript |
Blobby-Boi/uBlobeBM | main | ## Welcome to uBlobeBM (BlobeBM uBlock Edition)!
uBlobeBM is an exploit that can run bookmarklets using uBlock Origin. It's very useful if bookmarklets don't work on your device or if they are blocked by your administrator.
#### How to setup uBlobeBM
Make sure that you have uBlock Origin installed on your computer. If you dont, download it [here](https://chromewebstore.google.com/detail/ublock-origin/cjpalhdlnbpafiamejdnhcphjbkeiagm).
Go to `chrome-extension://cjpalhdlnbpafiamejdnhcphjbkeiagm/settings.html`
Check the "I am an advanced user" box, then click on the small gear ⚙️ icon. Find `userResourcesLocation` and change it from `unset` to `https://blobby-boi.github.io/uBlobeBM/blob.js`
Go to `chrome-extension://cjpalhdlnbpafiamejdnhcphjbkeiagm/1p-filters.html`
Add the following line of code:
```
*##+js(blob.js)
```
#### How to use uBlobeBM
Press CTRL + Shift + ~
Where it says "Enter bookmarklet here", enter the bookmarklet code. Then click on the green "Add Bookmarklet" button.
It will prompt you for how you want it to be called. Name it something that makes sense, because once you have a long list of bookmarklets, you want it to be easy to tell which one's which.
Once you enter the name, you should see the bookmarklet show up. It consists of 4 buttons: The blue button is to run the bookmarklet, the remove button is to delete the bookmarklet, and the other 2 buttons are to rename the bookmarklet and edit the bookmarklet. Hovering over the blue button for a few seconds reveals the bookmarklet code.
You can add as many bookmarklets as you need onto BlobeBM. The bookmarklets will save even if you close the window or shut down your device.
I hope this helps! :)
| A version of BlobeBM that uses the uBlock Run bypass but makes it better | bookmarklet,bookmarklet-unblocker,bypass,chromebook,javascript,javascript-bookmarklets,proxy,school-chromebook,school-computer,school-hacks | 2024-03-29T15:22:14Z | 2024-04-05T17:23:25Z | null | 1 | 0 | 69 | 1 | 2 | 4 | null | null | HTML |
hu8813/pong42 | main | ## WIP - Work in progress
# Pure JS (vanilla) frontend + Django backend
🏓 42 Transcendence 🏓 - This project, named pong42, is a school project for the ft_transcendence course. It features a Django backend paired with a pure JavaScript (vanilla JS) frontend.
### Screenshots
[Website](https://pong42.vercel.app)
| 🏓 42 transcendence 🏓 ft_transcendence school project with django backend and pure javascript frontend (vanilla js) pong42 | 42,ft-transcendence,javascript,pong,transcendence,vanilla,vanilla-javascript,vanilla-js,django,js | 2024-03-29T19:27:58Z | 2024-05-03T12:52:01Z | null | 4 | 0 | 807 | 0 | 0 | 4 | null | null | JavaScript |
adamlui/scss-to-css | main | null | { } Recursively compile all SCSS files into minified CSS. | api,cli,compiler,css,javascript,minifier,nodejs,sass,scss,stylesheets | 2024-04-16T15:16:04Z | 2024-05-22T09:49:53Z | 2024-05-14T20:39:46Z | 1 | 13 | 217 | 0 | 1 | 4 | null | NOASSERTION | JavaScript |
ritoncharlox/Responsive-Portfolio-Website | master | <br>
<h1 align=center>
<span> Responsive Portfolio Website </span>
<img align="center" src="./Assets/favicons/favicon.png" alt="" width="50" height="50">
</h1>
**This is a responsive portfolio website built using HTML, CSS, and JavaScript. It includes multiple pages showcasing various sections such as career information, education details, gallery, hobbies, skills, and testimonials. The contact page is fully functional and uses emailjs to send emails to users upon form submission.**
## Live Demo
You can view the live demo of this portfolio website on Netlify:
<br>
Netlify: [Responsive Portfolio Website](https://ritoncharlox-portfolio-website.netlify.app/)
## Pages
1. **Home:** Landing page introducing the portfolio.
2. **Career:** Information about career history and experience.
3. **Contact:** Functional contact form using emailjs to send emails.
4. **Education:** Details about educational background and qualifications.
5. **Gallery:** Gallery showcasing images or projects.
6. **Hobbies:** Section displaying hobbies and interests.
7. **Skills:** Information about technical skills and expertise.
8. **Testimonials:** Testimonials or reviews from clients or colleagues.
## Technologies Used
### Languages:
  
<br>
  
<br>
  
### Libraries/Frameworks:
  
## Features
- Fully responsive design, ensuring optimal viewing experience across devices.
- Functional contact form that sends emails to users upon submission.
- Multiple pages to showcase various aspects of the portfolio.
## Usage
To use this portfolio template for your own portfolio:
1. Clone this repository to your local machine.
```bash
git clone https://github.com/ritoncharlox/Responsive-Portfolio-Website.git
```
2. Customize the content of each page to reflect your own career, education, skills, etc.
3. If you want to use the contact form functionality:
- Sign up for an account on EmailJS and obtain your API keys.
- Replace the existing emailjs configuration in the JavaScript file with your own API keys.
## Contributing
Contributions to this project are welcome! If you have any suggestions, improvements, or bug fixes, feel free to fork this repository, make your changes, and submit a pull request.
## License
This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details. | Responsive Portfolio Website in html, css and js with working contact me page | css,css3,html,html-css-javascript,html5,javascript,portfolio,portfolio-website,responsive,responsive-portfolio | 2024-03-16T08:44:42Z | 2024-03-27T09:23:30Z | null | 1 | 0 | 3 | 0 | 0 | 4 | null | MIT | HTML |
archanaberry/Gacha-Design-Studio | DL | # Gacha Design Studio
# Tipe cabang (branch) repositori
* DL untuk edisi didownload agar bisa dimainkan resource game nya pakai game browser GachaDesignStudio.apk (com.lunime.githubcollab.archanaberry.gachadesignstudio)
* HS untuk edisi hosting online di vps/panel/termux agar bisa bantu dikembangkan untuk server dan dimainkan dengan bersama kolaborator tetapi harus pakai game browser khusus
# Ikon aplikasi web nya
Gacha Design Studio adalah sebuah game fanmade (buatan dari para penggemar) yang mengambil inspirasi dari Gacha Life 2 yang dikembangkan oleh Lunime. Game ini memungkinkan pemain untuk merancang karakter, memilih pakaian, dan menciptakan desain yang unik.
## Fitur Utama
| Fitur | Deskripsi |
|-------------------|----------------------------------------------------------------------------------------------|
| Pembuatan Karakter| Buat karakter unik dengan berbagai pilihan wajah, mata, rambut, dan aksesoris. |
| Desain Pakaian | Desain pakaian dengan berbagai motif, warna, dan gaya untuk karakter yang dibuat. |
| Studio Foto | Ambil foto karakter yang telah dibuat dalam berbagai pose dan latar belakang yang berbeda. |
| Mode Fashion Show | Tunjukkan desain pakaian terbaik Anda dalam kompetisi mode virtual dengan pemain lain. |
| Koleksi Item | Kumpulkan berbagai item fashion dan aksesoris untuk menambah variasi dalam desain Anda. |
| Berbagi karakter | Bagikan karakter anda untuk berkolaborasi dengan teman anda lewat kode karakter dan juga impor |
| Aset Vektor | Menjadikan kualitas gambar di karakter gacha mu jadi tajam dan tanpa penurunan kualitas hanya saja sedikit lagyy |
| Map Vektor | Sebuah map dunia fiktif permainan yang menjadikan nya sangat luas tanpa penurunan kualitas dan bisa di zoom |
| Studio Pose | Buatlah pose dengan mudah dengan gaya karakter yang anda inginkan dan animasi pose (untuk animasi ditunggu) |
| Bisa dimainkan secara offline | Kamu bebas memainkan game ini disaat tanpa ada kuota internet dengan sepuas puas nya UwU |
## Link
Kunjungi [Gacha Life 2 Assets](https://drive.google.com/file/d/1RKEoUYibFckKS10PS7cGm9bbfmgZJIp2/view?usp=drive_link) untuk berkustomisasi karakter yang anda inginkan UwU.
# Untuk saat ini versi aset nya masih v0.01_alpha...
## Cara buka?
Kamu tinggal download repositori ini dengan game browser "GachaDesignStudio.apk" nya, klik setuju pada penyimpanan, lalu tunggu sampai ke download semua resource zip nya.
Setelah berhasil download secara otomatis kebuka game nya di file `mainmenu.html` nya dan langsung rangkai sesuka mu XD
* Ini dia
## Cara menambahkan assets karakter ke studio poser
```
---
JavaScript
File: js/poser/main.js
---
const layers = [
// lapisan //
// Tangan kanan
new Layer('Lengan atas kanan', 'assets/arm1.svg', 'assets/arm2.svg', {flipX: true}),
new Layer('Lengan bawah kanan', 'assets/hand1.svg', 'assets/hand2.svg', {flipX: true}),
new Layer('Tangan kanan', 'assets/finger3.svg', 'assets/finger4.svg', {flipX: true}),
// Kaki kanan
new Layer('Paha atas kanan', 'assets/leg1.svg', 'assets/leg2.svg', {flipX: true}),
new Layer('Kaki kanan', 'assets/foot1.svg', 'assets/foot2.svg', {flipX: true}),
// Kepala
new Layer('Badan', 'assets/body1.svg', 'assets/body2.svg'),
// Badan
new Layer('Kepala', 'assets/head1.svg', 'assets/head2.svg'),
// Tangan kiri
new Layer('Lengan atas kiri', 'assets/arm1.svg', 'assets/arm2.svg'),
new Layer('Lengan bawah kiri', 'assets/hand1.svg', 'assets/hand2.svg'),
new Layer('Tangan kiri', 'assets/finger1.svg', 'assets/finger2.svg'),
// Kaki kiri
new Layer('Paha atas kiri', 'assets/leg1.svg', 'assets/leg2.svg'),
new Layer('Kaki kiri', 'assets/foot1.svg', 'assets/foot2.svg'),
// Lapisan //
// tambahkan dengan format //
// new Layer('Nama anggota tubuh', 'assets/anggotaBadanOutline.svg', 'tambahan...', 'assets/anggotaBadan.svg'),
// Jangan lupa diganti dan disesuaikan
// seperti ini ygy //
];
```
## Kekurangan dan Kendala
* ✅ Berhasil di tangani.
* ❎ Belum di tangani.
| Kekurangan | Deskripsi | Status |
|-----------------------------------------------|------------------------------------------------------------------------------------------------|--------|
| Keterbatasan Aset | Saat ini, game masih terbatas dalam jumlah aset yang tersedia karena baru dirilis. | ❎ |
| Karakter Dummy/Template | Karakter dalam game masih dalam bentuk dummy atau template kosong, belum memiliki rambut atau aksesori yang lengkap. | ❎ |
| Zoom Belum Aktif | Fitur zoom untuk melihat detail lebih jauh dalam pembuatan karakter atau desain pakaian masih belum aktif. | ✅ |
| Flip Vertikal dan Horizontal Bermasalah | Fitur flip vertikal dan horizontal saat ini mengalami masalah teknis yang membuatnya ngebug. | ✅ |
| Selektor Karakter Belum Aktif Sepenuhnya | Selektor karakter masih belum berfungsi sepenuhnya, sehingga pengguna belum dapat dengan mudah memilih karakter yang ingin dimodifikasi. | ✅ |
| Tidak Ada Fitur Berbagi Karakter dengan Kode atau Upload Aset SVG | Fitur untuk berbagi karakter menggunakan kode atau mengunggah aset SVG sebagai tambahan aset belum ditambahkan. | ❎ |
| Input box Lebar/Width, dan Tinggi/Height nya bermasalah | Ketika bisa diubah nilai nya tetapi tidak mengalami perubahan posisi | ❎ |
| Pengingat jika tidak sengaja ke refresh | Untuk mencegah kehilangan posisi pose ataupun rangkai karakter Gacha mu | ❎ |
| Belum ada main menu | Supaya terkesan ada menu awal permainan | ✅ |
| Belum ada BGM | Fitur untuk menyegarkan suasana dengan musik yang aesthetic agar tidak monoton (hanya saja harus pakai aplikasi apk dikhususkan!) | ✅ |
| Design UI/UX masih berantakan | Untuk menambah ke estetika game ini agar menarik pengunjung :3 | ❎ |
| Loading Main Menu | Berfungsi untuk meload semua source game web ini | ✅ |
| Sudah ditambah ikon thumbnail karakter | Ikon karakter agar mudah dicari dan menambah estetika profile karakter gacha mu :> | ❎ |
## Tangkapan Layar
* Main menu
Tablet 1200x2000 (Portrait mode)
* Mode Studio Pose
Tablet 2000x1200 (Landscape mode)
PC/Laptop 1366x768 (Landscape mode)
Diperbarui
## Bahasa pemrograman yang dipakai
<img src="archanaberry/HTML.png" alt="HTML versi 5" width="192" height="108">
<img src="archanaberry/htmx.png" alt="HTML dengan dukungan JavaScript" width="192" height="108">
<img src="archanaberry/CSS.png" alt="Dukungan CSS" width="192" height="108">
| Specialy forked fanmade Lunime's Game | avatar-maker,character-creation,character-generator,css,gacha,gacha-club,gacha-life,javascript,lunime,mod | 2024-04-15T18:53:38Z | 2024-05-12T14:54:44Z | null | 3 | 8 | 178 | 1 | 3 | 4 | null | null | JavaScript |
IryDev/twitter-clone-laravel | main | <div align="center">
<br />
<img src="https://github.com/IryDev/twitter-clone-laravel/assets/86270481/08552ffb-cb53-4771-afbd-b103a574b8c9" alt="Project Banner">
<br />
<div>
<img src="https://img.shields.io/badge/Laravel-FF2D20?style=for-the-badge&logo=laravel&logoColor=white" alt="react.js" />
<img src="https://img.shields.io/badge/-Tailwind_CSS-black?style=for-the-badge&logoColor=white&logo=tailwindcss&color=06B6D4" alt="tailwindcss" />
<img src="https://img.shields.io/badge/JavaScript-F7DF1E?style=for-the-badge&logo=JavaScript&logoColor=black" alt="javascript" />
<img src="https://img.shields.io/badge/PostgreSQL-316192?style=for-the-badge&logo=postgresql&logoColor=white" alt="PostgreSQL" />
</div>
<h1 align="center">A X (Twitter) Clone Fullstack Application</h3>
<div align="center">
Explore this project and delve into its features. Elevate your skills with this Twitter clone crafted with passion by <a href="https://rey-kosso-portfolio.vercel.app" target="_blank"><b>IryDev</b></a>.
</div>
</div>
## 📋 <a name="table">Table of Contents</a>
1. 🤖 [Introduction](#introduction)
2. ⚙️ [Tech Stack](#tech-stack)
3. 🔋 [Features](#features)
4. 🤸 [Quick Start](#quick-start)
5. 🚀 [Plus](#plus)
## <a name="introduction">🤖 Introduction</a>
Explore social media with this user-friendly platform that has a nice look and lots of features. Easily create and explore posts, and enjoy a strong authentication system and quick data fetching using React Query for a smooth user experience.
## <a name="tech-stack">⚙️ Tech Stack</a>
- Laravel
- PostgresSQL
- JavaScript
- Tailwind CSS
## <a name="features">🔋 Features</a>
👉 **Authentication System**: A robust authentication system ensuring security and user privacy
👉 **Like and Save Functionality**: Enable users to like and save posts
👉 **Profile Page**: A user profile page showcasing liked posts and providing options to edit the profile
👉 **Create Post**: Implement a user-friendly form to create post page with effortless file management, storage
👉 **Edit Post**: Provide users with the ability to edit the content of their posts at any time
## <a name="quick-start">🤸 Quick Start</a>
Follow these steps to set up the project locally on your machine.
**Prerequisites**
Make sure you have the following installed on your machine:
- [Git](https://git-scm.com/)
- [Node.js](https://nodejs.org/en)
- [npm](https://www.npmjs.com/) (Node Package Manager)
- [composer](https://getcomposer.org/) (A Dependency Manager for PHP)
**Cloning the Repository**
```bash
git clone https://github.com/IryDev/twitter-clone-laravel.git
cd twitter-clone-laravel
```
**Installation**
Install the project javascript dependencies using npm:
```bash
npm install
```
Install the project laravel dependencies using composer:
```bash
composer install
```
**Set Up Environment Variables**
Create a new file named `.env` in the root of your project and add the following content:
```env
DB_CONNECTION=
DB_HOST=
DB_PORT=
DB_DATABASE=
DB_USERNAME=
DB_PASSWORD=
```
**Running the Project**
```bash
php artisan serve
```
Open [http://localhost:8000](http://localhost:8000) in your browser to view the project.
## 🚀 Plus
### You like or wanna fork it ? Give it a Star ⭐️ !
| A Twitter Clone fullstack app with the same UI as the original and great performance using Laravel, PostgresSQL, Tailwind, and more. | php,twitter,twitter-clone,laravel,tailwind,tailwindcss,postgresql,laravel-framework,x-clone,javascript | 2024-03-21T15:47:35Z | 2024-04-18T21:08:24Z | null | 1 | 0 | 3 | 0 | 0 | 4 | null | null | PHP |
Hatmic/Homepage-old.hatmic.com | main | # hatmic.com
### 简介
[hatmic.com](https://hatmic.com) 是由 [Hatmic](https://github.com/Hatmic) 自主开发的开源个人主页网页，并开源在公共仓库中，你可以在 [GitHub - Hatmic/Homepage-hatmic.com](https://github.com/Hatmic/Homepage-hatmic.com) 获取源码。
网页使用 HTML + CSS + JavaScript 开发，分别位于 index.html、style、script 中。并将网页中涉及的文本、图片等信息存储在 data.jsonnet 中。
欢迎 star 和 fork 我的项目，也欢迎关注我！
### 克隆到本地
你需要先安装 Git。
打开你想克隆到的文件夹，打开终端。
输入 `git clone https://github.com/Hatmic/Homepage-hatmic.com.git`，等待片刻后发现文件已经克隆到你的文件夹中。
### Introduction
[hatmic.com](https://hatmic.com) is an open-source personal homepage web page independently developed by [Hatmic](https://github.com/Hatmic) and open-sourced in a public repository. You can obtain the source code at [GitHub - Hatmic/Homepage-hatmic.com](https://github.com/Hatmic/Homepage-hatmic.com).
The webpage is developed using HTML + CSS + JavaScript, located in index.html, style, and script respectively. The text, images, and other information involved in the webpage are stored in data.jsonnet.
Welcome to star and fork my project, and also feel free to follow me!
### Clone to Local
You need to install Git first.
Open the folder you want to clone to and open the terminal.
Type `git clone https://github.com/Hatmic/Homepage-hatmic.com.git`, wait for a moment, and you will find that the files have been cloned into your folder.
| 个人主页 Personal HomePage | css,homepage,html,javascript,js,web,hatmic,ui-design,ux-design | 2024-04-12T18:44:22Z | 2024-04-23T13:16:51Z | null | 1 | 0 | 28 | 0 | 1 | 4 | null | null | JavaScript |
DEENUU1/OpenNote | main | [![Contributors][contributors-shield]][contributors-url]
[![Forks][forks-shield]][forks-url]
[![Stargazers][stars-shield]][stars-url]
[![Issues][issues-shield]][issues-url]
[![MIT License][license-shield]][license-url]
[![LinkedIn][linkedin-shield]][linkedin-url]
<br />
<div align="center">
<h3 align="center">OpenNote</h3>
<strong align="center">
OpenNote allows you to process files, videos and articles and create notes/summaries with just a few clicks. The whole app is supported by local AI models.
<br />
<br />
<a href="https://github.com/DEENUU1/OpenNote/issues">Report Bug</a>
·
<a href="https://github.com/DEENUU1/OpenNote/issues">Request Feature</a>
</strong>
</div>
<img src="assets/home.png" alt="home_page"/>
<img src="assets/details1.png" alt="details_page_1"/>
<img src="assets/details2.png" alt="details_page_2"/>
## TODO
- [ ] Add support for Whisper API
- [ ] Translator
## About the project
### Main Idea
The goal of this project was to make learning new things easier. The program was created for my own use, but I provide it with full support in the future.
This project allows you to create notes or summarize using LOCAL artificial intelligence models. The program does not require a penny to run (unless we are talking about a slightly better computer)
The user can enter text manually, provide a link to an article, a YouTube video or a file in .PDF or .TXT format
Then, after initial data processing, the program allows you to create notes/summaries using artificial intelligence.
### Preprocessing
<img src="assets/preprocess.png" alt="preprocess_architecture"/>
As I mentioned, the project allows you to provide various data sources. I will try to briefly discuss each of them.
#### Text input
Here, the user can manually enter the text that he would like to process
#### Online article
Thanks to the Selenium framework and page content parsing, it is enough to provide a link to any article on the Internet and the program will automatically download the entire page content and then save all the text contained in the h1, h2, h3, h4, h5 and p
#### Youtube video
In this case, two solutions were used.
First, the program checks whether subtitles have already been added manually or generated for this film. Most videos have subtitles turned on, but there are some without them. Then the program automatically downloads the movie as an .mp3 file and then divides it into parts - 2.5 minutes each.
Then, using the Whisper model, which also works locally and does not require any costs, it creates a transcription of the entire video.
#### PDF, TXT file
Here the principle of operation is similar to `Text input`, the file is saved and then it is parsed to extract all the text from it
### Process
<img src="assets/process.png" alt="process_architecture"/>
Processing involves loading previous data and then dividing it into parts so that they fit into the context of the language model. Then, a note/summary is created for each of these parts.
Once all the parts have been processed, they are combined and saved to the database.
Everything is done by using artificial intelligence models that run locally on the computer.
## Technologies:
- Python
- FastAPI
- Selenium
- Beautiful Soup 4
- SQLite
- Docker
- Javascript
- HTML, CSS, Bootstrap
- Powershell
- Ollama
- Whisper
- OpenAI
- Groq
## Installation
### Clone repository
```bash
git clone https://github.com/DEENUU1/property-aggregator.git
```
### Create .env file
```bash
cp .env_example .env
```
#### How to set up AI models in .env file
`LLM_MODEL` (OPTIONAL) If you want to use Ollama here you can select one of model from this list https://ollama.com/library (codegemma, gemma, llama2, mistral, ...) <br><br>
`OPENAI_APIKEY` (OPTIONAL) If you want to use OpenAI with models (GPT4/GPT3.5-Turbo) here you can add your API KEY <br><br>
`GROQ_APIKEY` (OPTIONAL) If you want to use GROQ API with models (Llama3/Llama2 etc.) here you can add API KEY <br><br>
`WHISPER_MODEL` (OPTIONAL) here you can select one of model from this list https://github.com/openai/whisper (tiny, base, small, medium, large) <br>
### (OPTIONAL) Install FFmpeg on your machine
It's available on Windows, MacOS and Linux
https://ffmpeg.org/download.html
### (OPTIONAL) Install Ollama to manage LLM models
https://ollama.com/
### Option 1 - Run app by using Docker
```bash
# Build Docker image
docker build -t app .
# Run container
docker run app
```
### Option 2 - Run app with Powershell script
This is a great option if you are using Windows.
Right click on `run.ps1` file and click `Run With Powershell`
### Option 3 - Run with command
```bash
pip install -r requirements.txt
cd ./src
python app.py
```
## Authors
- [@DEENUU1](https://www.github.com/DEENUU1)
<!-- LICENSE -->
## License
See `LICENSE.txt` for more information.
<!-- MARKDOWN LINKS & IMAGES -->
<!-- https://www.markdownguide.org/basic-syntax/#reference-style-links -->
[contributors-shield]: https://img.shields.io/github/contributors/DEENUU1/OpenNote.svg?style=for-the-badge
[contributors-url]: https://github.com/DEENUU1/OpenNote/graphs/contributors
[forks-shield]: https://img.shields.io/github/forks/DEENUU1/OpenNote.svg?style=for-the-badge
[forks-url]: https://github.com/DEENUU1/OpenNote/network/members
[stars-shield]: https://img.shields.io/github/stars/DEENUU1/OpenNote.svg?style=for-the-badge
[stars-url]: https://github.com/DEENUU1/OpenNote/stargazers
[issues-shield]: https://img.shields.io/github/issues/DEENUU1/OpenNote.svg?style=for-the-badge
[issues-url]: https://github.com/DEENUU1/OpenNote/issues
[license-shield]: https://img.shields.io/github/license/DEENUU1/OpenNote.svg?style=for-the-badge
[license-url]: https://github.com/DEENUU1/OpenNote/blob/master/LICENSE.txt
[linkedin-shield]: https://img.shields.io/badge/-LinkedIn-black.svg?style=for-the-badge&logo=linkedin&colorB=555
[linkedin-url]: https://linkedin.com/in/kacper-wlodarczyk
[basic]: https://github.com/DEENUU1/OpenNote/blob/main/assets/v1_2/basic.gif?raw=true
[full]: https://github.com/DEENUU1/OpenNote/blob/main/assets/v1_2/full.gif?raw=true
[search]: https://github.com/DEENUU1/OpenNote/blob/main/assets/v1_2/search.gif?raw=true
| 🧠 Talk with Youtube videos, web articles, files and text. Powered by Groq, Ollama and OpenAI | bootstrap,css,docker,fastapi,html,javascript,jinja2,langchain,llama2,llm | 2024-04-12T12:48:13Z | 2024-05-04T11:54:31Z | 2024-05-04T11:49:24Z | 1 | 0 | 52 | 0 | 0 | 4 | null | MIT | Python |
No-Country/c17-05-m-node-react | main | <div align="center">
<img src="./readme-data/Health Link - Logo.png" width="100px" alt="Health Link Logo">
<h1>Bienvenido a Health Link!</h1>
</div>
Health link fue creada con la visión de hacer que la atención médica sea más accesible, conveniente y efectiva para todos. En muchas ocasiones, las barreras geográficas, los largos tiempos de espera y la dificultad para acceder a especialistas médicos eran obstáculos significativos para muchas personas en la búsqueda de atención médica oportuna y de calidad.
Con esta preocupación en mente, decidimos desarrollar una solución que permitiera a las personas recibir atención médica de forma remota, desde la comodidad de sus hogares o desde cualquier lugar donde se encuentren. Health link no solo ofrece consultas médicas virtuales con profesionales altamente calificados, sino que también facilita la gestión de recetas, el seguimiento de tratamientos y la obtención de asesoramiento médico especializado sin la necesidad de desplazamientos.
## 🚀 Deploy
- Frontend: <a href="https://health-link-web.onrender.com" target="_blank">[Link a la pagina web]</a>
- Backend: <a href="https://health-link-api.onrender.com" target="_blank">[Link a la API]</a>
- Swagger UI: <a href="https://health-link-api.onrender.com/docs" target="_blank">[Link a documentacion en Swagger]<a/>
>[!WARNING]
>El backend esta deployado en OnRender, por lo cual existe la posibilidad de que haya 50 segundos de delay
## 🎨 Figma
- Protipo: <a href="https://www.figma.com/proto/QVVfdADrJhPL4fk9IGfXeL/Untitled?type=design&node-id=363-1695&t=xAfAic6Vtaok4IGs-0&scaling=scale-down&page-id=0%3A1&starting-point-node-id=8%3A1413" target="_blank">[Link al prototipo]</a>
- Diseño: <a href="https://www.figma.com/file/QVVfdADrJhPL4fk9IGfXeL/Untitled?type=design&node-id=363-1695&mode=design" target="_blank">[Link al diseño]</a>
## 🛠️ Tecnologias
### Frontend
[](https://skillicons.dev)
### Backend
[](https://skillicons.dev)
### Desarrollo y testing
[](https://skillicons.dev)
## 📈 Diagrama entidad-relación
<div align="center">
<img src="./readme-data/Database - Diagrama entidad-relacion.png" width="650px" alt="Diagrama entidad-relacion"/>
</div>
## ⚙️ Instalacion y ejecución
Para ejecutar el proyecto de manera local se deben seguir los siguientes pasos:
1. Clonar el repo
>[!NOTE]
>Los siguientes pasos se deben aplicar tanto para la carpeta api como para la carpeta client
2. Instalación de dependencias
```bash
npm install
```
3. Se debe crear un archivo .env en el mismo sitio donde se encuentra el archivo .env.example y siguiendo sus instrucciones
4. Ejecución del proyecto
```bash
npm run dev
```
> [!WARNING]
> Tener en cuenta que sin la ejecución de la API el Frontend no va a funcionar
## 📷 Capturas
<div align="center">
<img src="./readme-data/Web - Landing.png" width="400px" alt="Landing page">
<img src="./readme-data/Web - Signup.png" width="400px" alt="Signup">
<img src="./readme-data/Web - Login.png" width="400px" alt="Login">
<img src="./readme-data/Web - Home.png" width="400px" alt="Home">
<img src="./readme-data/Web - Teleconsults.png" width="400px" alt="Teleconsults">
<img src="./readme-data/Web - Chats.png" width="400px" alt="Chats">
<img src="./readme-data/Web - Chat.png" width="400px" alt="Chat">
<img src="./readme-data/Web - Profile.png" width="400px" alt="Profile">
</div>
## 🫂 Equipo
<table align="center">
<tr>
<td valing="top">
<a href="https://www.linkedin.com/in/rosariobelen" target="_blank">
<img src="./readme-data/Team - Rosario Belen.jpg" width="150px" height="150px" alt="Rosario Belen">
<p align="center">Rosario Belen</p>
<p align="center">Diseño UX/UI</p>
</a>
</td>
<td valing="top">
<a href="https://www.linkedin.com/in/jorge-sifuentes-vera" target="_blank">
<img src="./readme-data/Team - Jorge Sifuentes.jpg" width="150px" height="150px" alt="Jorge Sifuentes">
<p align="center">Jorge Sifuentes</p>
<p align="center">Tester QA</p>
</a>
</td>
<td valing="top">
<a href="https://www.linkedin.com/in/lucas-escudero-54195322b" target="_blank" alt="Rosario Belen">
<img src="./readme-data/Team - Lucas Escudero.jpg" width="150px" height="150px" alt="Lucas Escudero">
<p align="center">Lucas Escudero</p>
<p align="center">Fullstack Developer</p>
</a>
</td>
</tr>
</table>
## 👏🏻 Agradecimientos
<div align="center">
<img src="./readme-data//No country - Logo.png" align="center" width="250px"/>
</div>
| Health link es una aplicacion web que busca conectar medicos con pacientes de una forma simple y efectiva. | css3,express,git,html5,javascript,mysql,node,react,redux-toolkit,sequelize | 2024-03-29T15:40:20Z | 2024-04-29T22:50:50Z | null | 7 | 3 | 108 | 0 | 0 | 4 | null | MIT | JavaScript |
Ilvondir/fancy-blog | master | # Fancy Blog
Fancy Blog is a web application built using the Laravel framework with an MVC architecture, meaning it is server-side application. The visual design of the application has been crafted using the Materialize framework.
The application showcases popular aspects of social media services such as tags and comments, which are represented in the database as many-to-many and one-to-many relationships, respectively.
For guests, the application allows browsing blog articles and registering. Logged-in users can additionally comment on all articles. Users in the journalist role can add new tags, write articles and edit their own. The administrator has full control over tags, articles, and comments.
## Used Tools
- HTML 5
- CSS 3
- JavaScript ES6
- PHP 8.3.6
- Laravel 11.4.0
- Materialize 1.0.0
- Font Awesome 6.5.2
## Requirements
For running the application you need:
- [MySQL](https://www.mysql.com)
- [PHP](https://www.php.net/manual/en/install.windows.php)
- [composer](https://getcomposer.org)
## How to run
1. Execute command `git clone https://github.com/Ilvondir/fancy-blog`.
2. Create `fancy_blog` database.
3. Run `start.bat` file.
4. Log in to the selected account to discover various functionalities.
| Account | Email | Password |
|:---------------:|:---------------------:|:-----------:|
| Administrator | admin@fb.com | password |
| Journalist | journalist@fb.com | password |
| User | user@fb.com | password |
## First Look
| MVC application of a blog created in Laravel. | blade,css,eloquent,fakerphp,font-awesome,html,javascript,laravel,materialize,php | 2024-04-09T16:11:49Z | 2024-04-18T20:09:51Z | null | 1 | 1 | 43 | 0 | 0 | 4 | null | MIT | PHP |
maumitasarkar16/youtube-clone | main | # Getting Started with Create React App
This project was bootstrapped with [Create React App](https://github.com/facebook/create-react-app).
## Available Scripts
In the project directory, you can run:
### `npm start`
Runs the app in the development mode.\
Open [http://localhost:3000](http://localhost:3000) to view it in your browser.
The page will reload when you make changes.\
You may also see any lint errors in the console.
### `npm test`
Launches the test runner in the interactive watch mode.\
See the section about [running tests](https://facebook.github.io/create-react-app/docs/running-tests) for more information.
### `npm run build`
Builds the app for production to the `build` folder.\
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.\
Your app is ready to be deployed!
See the section about [deployment](https://facebook.github.io/create-react-app/docs/deployment) for more information.
### `npm run eject`
**Note: this is a one-way operation. Once you `eject`, you can't go back!**
If you aren't satisfied with the build tool and configuration choices, you can `eject` at any time. This command will remove the single build dependency from your project.
Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except `eject` will still work, but they will point to the copied scripts so you can tweak them. At this point you're on your own.
You don't have to ever use `eject`. The curated feature set is suitable for small and middle deployments, and you shouldn't feel obligated to use this feature. However we understand that this tool wouldn't be useful if you couldn't customize it when you are ready for it.
## Learn More
You can learn more in the [Create React App documentation](https://facebook.github.io/create-react-app/docs/getting-started).
To learn React, check out the [React documentation](https://reactjs.org/).
### Code Splitting
This section has moved here: [https://facebook.github.io/create-react-app/docs/code-splitting](https://facebook.github.io/create-react-app/docs/code-splitting)
### Analyzing the Bundle Size
This section has moved here: [https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size](https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size)
### Making a Progressive Web App
This section has moved here: [https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app](https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app)
### Advanced Configuration
This section has moved here: [https://facebook.github.io/create-react-app/docs/advanced-configuration](https://facebook.github.io/create-react-app/docs/advanced-configuration)
### Deployment
This section has moved here: [https://facebook.github.io/create-react-app/docs/deployment](https://facebook.github.io/create-react-app/docs/deployment)
### `npm run build` fails to minify
This section has moved here: [https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify](https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify)
| This is YouTube clone app in React and Tailwind CSS. It shows Most popular videos,Auto-complete search suggestions,Search videos based on the query input in the search bar, Video details like Channel name, video title, views, and likes,Nested Comments using YouTube APIs. Like/Unlike button in the watch page & Dummy Live Chat. Compatible on Laptops | javascript,react,tailwindcss,youtube-api,redux-toolkit | 2024-04-20T04:18:05Z | 2024-04-23T14:14:36Z | null | 1 | 0 | 6 | 0 | 0 | 4 | null | null | JavaScript |
nieyuyao/webp-wasm | main | # webp.wasm
webp.wasm is a pure Webassembly / Javascript port of libwebp. The library supports encoding animated WebP.
## Install
```shell
npm i wasm-webp
```
## APIs
### Encode
#### encode
Get encoder encoderVersion.
`function encoderVersion(): Promise<string>`
##### Example
```javascript
const version = await encoderVersion()
console.log(version) // 1.3.2
```
#### encodeRGB
Encodes rgb bitmap an returns WebP Uint8Array. The `width` and `height` parameters of the bitmap should be provided.
`function encodeRGB(rgb: Uint8Array, width: number, height: number, quality?: number): Promise<Nullable<Uint8Array>>`
##### Example
```javascript
...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const buf = new Uint8Array(3 * canvas.width, canvas.height)
let j = 0
// remove alpha
imgData.data.forEach((pixel, i) => {
if ((i + 1) % 4 === 0) {
return
}
buf[j] = pixel
j++
})
const webpData = await encodeRGB(buf, canvas.width, canvas.height)
const blob = new Blob([webpData!], {type: 'image/webp'})
const blobURL = URL.createObjectURL(blob);
// download webp
const a = document.createElement('a')
a.download = '1.webp'
a.href = blobURL
document.body.appendChild(a)
a.click()
a.remove()
```
#### encodeRGBA
Encodes rgba bitmap an returns WebP Uint8Array.
`function encodeRGBA(rgba: Uint8Array, width: number, height: number, quality?: number): Promise<Nullable<Uint8Array>>`
##### Example
```javascript
...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const webpData = await encodeRGBA(imgData.data, canvas.width, canvas.height)
// download webp
...
```
#### encode
A more advanced API is based on the WebPConfig. <b>Only the lossless and quality parameters are supported now !!!</b>. You can generate low-quality webp with this function.
`function encodeRGBA(data: Uint8Array, width: number, height: number, hasAlpha: boolean,config: Partial<WebPConfig>): Promise<Nullable<Uint8Array>>`
- hasAlpha: `boolean`
Whether to include alpha chanel.
- WebPConfig.lossless: `number`
Lossless encoding (0=lossy(default), 1=lossless).
- WebPConfig.quality: `number`
Between 0 and 100. Default value is 100.
##### Example
```javascript
...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const webpData = await encode(imgData.data, canvas.width, canvas.height, true, { lossless: 0 })
// download webp
...
```
#### encodeAnimation
Returns animated WebP like `GIF`.
`function encodeAnimation(width: number, height: number, hasAlpha: boolean, frames: WebPAnimationFrame[]): Promise<Nullable<Uint8Array>>`
- hasAlpha: `boolean`
Whether to include alpha chanel.
The WebPAnimationFrame has follow properties:
- WebPAnimationFrame.data: `Uint8Array`
Frame bitmap.
- WebPAnimationFrame.duration: `number`
Duration of frame.
##### Example
```javascript
...
// record each frame
frames.push({
data: ctx.getImageData(0, 0, 100, 100).data,
duration: 20
})
const webpData = await encodeAnimation(100, 100, true, frames)
...
// download webp
```
### Decode
#### decoderVersion
Get decoder version.
`function decoderVersion(): Promise<string>`
##### Example
```javascript
const version = await decoderVersion()
console.log(version) // 1.3.2
```
#### decodeRGB
Decodes webp and outputs `WebPDecodedImageData` contains rgb bitmap.
`function decodeRGB(data: Uint8Array): Promise<Nullable<WebPDecodedImageData>>`
##### Example
```javascript
...
const fr = new FileReader()
fr.onload = () => {
if (!fr.result) {
return
}
webpData = fr.result as Uint8Array
const result = await decodeRGB(webpData)
// draw imageData
const ctx = canvas.getContext('2d')!
ctx.clearRect(0, 0, canvas.width, canvas.height)
canvas.style.width = `${result.width}px`
canvas.style.height = `${result.height}px`
canvas.width = result.width
canvas.height = result.height
ctx.putImageData(new ImageData(new Uint8ClampedArray(result.data)), 0, 0)
}
// read webp file
fr.readAsArrayBuffer(file)
...
```
#### decodeRGBA
Decodes webp and outputs `WebPDecodedImageData` contains rgba bitmap.
`function decodeRGB(data: Uint8Array): Promise<Nullable<WebPDecodedImageData>>`
##### Example
```javascript
...
const fr = new FileReader()
fr.onload = () => {
if (!fr.result) {
return
}
webpData = fr.result as Uint8Array
const result = await decodeRGBA(webpData)
// draw imageData
...
}
// webp file
fr.readAsArrayBuffer(file)
...
```
#### decodeAnimation
Decoding animated WebP image. Returns an array of frames.
`function decodeAnimation(data: Uint8Array, hasAlpha: boolean): Promise<Nullable<DecodedWebPAnimationFrame[]>>`
##### Example
```javascript
...
const fr = new FileReader()
fr.onload = () => {
if (!fr.result) {
return
}
webpData = fr.result as Uint8Array
const result = await decodeRGBA(webpData)
// draw imageData
...
}
// webp file
fr.readAsArrayBuffer(file)
...
```
#### DecodedWebPAnimationFrame
The object have the following properties:
- DecodedWebPAnimationFrame.width: `number`
The frame image width.
- DecodedWebPAnimationFrame.height: `number`
The frame image height.
- DecodedWebPAnimationFrame.duration: `number`
The frame display duration.
- DecodedWebPAnimationFrame.data: `Uint8Array`
Raw data in pixels.
#### WebPDecodedImageData
The object have the following properties:
- WebPDecodedImageData.width: `number`
The image width in pixels.
- WebPDecodedImageData.height: `number`
The image height in pixels.
- WebPDecodedImageData.data: `Uint8Array`
Raw data in pixels.
> Note: It has same properties as browser `ImageData` object, but it is not. There is actually no `ImageData` in node.
## Playing Examples
```shell
npm run build-wasm:dev && npm run dev
```
## Building
```shell
npm run build
``` | A webp wasm library based on libwebp. | decoder,encoder,libwebp,wasm,webp,animation,javascript,webassembly | 2024-04-01T02:11:06Z | 2024-05-15T02:06:13Z | 2024-04-12T15:20:50Z | 2 | 4 | 21 | 0 | 0 | 4 | null | MIT | JavaScript |
Aman254/PrimeFitnessStudio | master | # Prime Fitness Gym Website
Welcome to the Prime Fitness Gym Website repository! This repository contains the codebase for our gym's website.
## Project Setup
### Cloning the Project
```bash
git clone <repository-url>
```
### Backend Setup
```bash
cd backend
npm install
```
#### Backend Configuration
Create a file named `config.env` in the `backend` folder and add the following environment variables:
```
PORT=5000
DATABASE=<YOUR_MONGODB_URI>
JWT_SECRET=<YOUR_JWT_SECRET>
JWT_EXPIRES_IN=90d
```
### Frontend Setup
```bash
cd frontend
npm install
```
#### Frontend Configuration
Create a file named `.env` in the root of the `frontend` folder and add the following environment variable:
```
REACT_APP_API_URL=http://localhost:5000/api/v1
```
#### Import Development Data
In the backend folder, navigate to the data folder and run the following command:
```bash
cd backend/Data/data
node import-dev-data.js
```
## Usage
Once you've set up the project, you can run the backend and frontend servers:
### Run Backend Server
```bash
cd backend
npm start
```
### Run Frontend Server
```bash
cd frontend
npm start
```
| This project is aimed at creating a comprehensive website for Prime Fitness Gym, providing information about the gym, its facilities, trainers, and schedules. And Workouts for Different Body Parts | backend,backend-api,front-end-development,full-stack,javascript,mern-stack,react,reactjs | 2024-04-08T18:54:13Z | 2024-05-01T11:24:55Z | null | 3 | 4 | 35 | 0 | 3 | 4 | null | null | JavaScript |
danieleverest/reactjs-interview-questions | main | # React Interview Questions & Answers
> Click :star:if you like the project. Pull Request are highly appreciated. Follow me [@danieleverest18](https://twitter.com/danieleverest18) for technical updates.
---
<div>
<p align="center">
<a href=https://react.gg/?s=rjsiq>
<img src="./images/collab/uidev-banner4x.png" alt="React interview" width="100%">
</a>
</p>
</div>
---
<div>
<p align="center">
<a href=https://zerotomastery.io/?utm_source=github&utm_medium=sponsor&utm_campaign=reactjs-interview-questions>
<img src=https://process.fs.teachablecdn.com/ADNupMnWyR7kCWRvm76Laz/resize=height:70/https://www.filepicker.io/api/file/AKYtjj5SSGyJuyZrkAB2 alt="ZTM Logo" width="100" height="50">
</a>
<ol>
<li>I recommend this <a href="https://links.zerotomastery.io/react_sudheer">React course</a> if you’re serious about learning React and want to go beyond the basics</li>
<li>Want to ace your coding interview and get hired at your dream company? <a href="http://links.zerotomastery.io/mci_sudheer">Take this coding interview bootcamp</a></li>
</ol>
</p>
</div>
---
**Note:** This repository is specific to ReactJS. Please check [Javascript Interview questions](https://github.com/sudheerj/javascript-interview-questions) for core javascript questions.
### Table of Contents
| No. | Questions |
| --- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| | **Core React** |
| 1 | [What is React?](#what-is-react) |
| 2 | [What is the history behind React evolution?](#What-is-the-history-behind-React-evolution) |
| 3 | [What are the major features of React?](#what-are-the-major-features-of-react) |
| 4 | [What is JSX?](#what-is-jsx) |
| 5 | [What is the difference between Element and Component?](#what-is-the-difference-between-element-and-component) |
| 6 | [How to create components in React?](#how-to-create-components-in-react) |
| 7 | [When to use a Class Component over a Function Component?](#when-to-use-a-class-component-over-a-function-component) |
| 8 | [What are Pure Components?](#what-are-pure-components) |
| 9 | [What is state in React?](#what-is-state-in-react) |
| 10 | [What are props in React?](#what-are-props-in-react) |
| 11 | [What is the difference between state and props?](#what-is-the-difference-between-state-and-props) |
| 12 | [Why should we not update the state directly?](#why-should-we-not-update-the-state-directly) |
| 13 | [What is the purpose of callback function as an argument of setState()?](#what-is-the-purpose-of-callback-function-as-an-argument-of-setstate) |
| 14 | [What is the difference between HTML and React event handling?](#what-is-the-difference-between-html-and-react-event-handling) |
| 15 | [How to bind methods or event handlers in JSX callbacks?](#how-to-bind-methods-or-event-handlers-in-jsx-callbacks) |
| 16 | [How to pass a parameter to an event handler or callback?](#how-to-pass-a-parameter-to-an-event-handler-or-callback) |
| 17 | [What are synthetic events in React?](#what-are-synthetic-events-in-react) |
| 18 | [What are inline conditional expressions?](#what-are-inline-conditional-expressions) |
| 19 | [What is "key" prop and what is the benefit of using it in arrays of elements?](#what-is-key-prop-and-what-is-the-benefit-of-using-it-in-arrays-of-elements) |
| 20 | [What is the use of refs?](#what-is-the-use-of-refs) |
| 21 | [How to create refs?](#how-to-create-refs) |
| 22 | [What are forward refs?](#what-are-forward-refs) |
| 23 | [Which is preferred option with in callback refs and findDOMNode()?](#which-is-preferred-option-with-in-callback-refs-and-finddomnode) |
| 24 | [Why are String Refs legacy?](#why-are-string-refs-legacy) |
| 25 | [What is Virtual DOM?](#what-is-virtual-dom) |
| 26 | [How Virtual DOM works?](#how-virtual-dom-works) |
| 27 | [What is the difference between Shadow DOM and Virtual DOM?](#what-is-the-difference-between-shadow-dom-and-virtual-dom) |
| 28 | [What is React Fiber?](#what-is-react-fiber) |
| 29 | [What is the main goal of React Fiber?](#what-is-the-main-goal-of-react-fiber) |
| 30 | [What are controlled components?](#what-are-controlled-components) |
| 31 | [What are uncontrolled components?](#what-are-uncontrolled-components) |
| 32 | [What is the difference between createElement and cloneElement?](#what-is-the-difference-between-createelement-and-cloneelement) |
| 33 | [What is Lifting State Up in React?](#what-is-lifting-state-up-in-react) |
| 34 | [What are the different phases of component lifecycle?](#what-are-the-different-phases-of-component-lifecycle) |
| 35 | [What are the lifecycle methods of React?](#what-are-the-lifecycle-methods-of-react) |
| 36 | [What are Higher-Order components?](#what-are-higher-order-components) |
| 37 | [How to create props proxy for HOC component?](#how-to-create-props-proxy-for-hoc-component) |
| 38 | [What is context?](#what-is-context) |
| 39 | [What is children prop?](#what-is-children-prop) |
| 40 | [How to write comments in React?](#how-to-write-comments-in-react) |
| 41 | [What is the purpose of using super constructor with props argument?](#what-is-the-purpose-of-using-super-constructor-with-props-argument) |
| 42 | [What is reconciliation?](#what-is-reconciliation) |
| 43 | [How to set state with a dynamic key name?](#how-to-set-state-with-a-dynamic-key-name) |
| 44 | [What would be the common mistake of function being called every time the component renders?](#what-would-be-the-common-mistake-of-function-being-called-every-time-the-component-renders) |
| 45 | [Is lazy function supports named exports?](#is-lazy-function-supports-named-exports) |
| 46 | [Why React uses className over class attribute?](#why-react-uses-classname-over-class-attribute) |
| 47 | [What are fragments?](#what-are-fragments) |
| 48 | [Why fragments are better than container divs?](#why-fragments-are-better-than-container-divs) |
| 49 | [What are portals in React?](#what-are-portals-in-react) |
| 50 | [What are stateless components?](#what-are-stateless-components) |
| 51 | [What are stateful components?](#what-are-stateful-components) |
| 52 | [How to apply validation on props in React?](#how-to-apply-validation-on-props-in-react) |
| 53 | [What are the advantages of React?](#what-are-the-advantages-of-react) |
| 54 | [What are the limitations of React?](#what-are-the-limitations-of-react) |
| 55 | [What are error boundaries in React v16](#what-are-error-boundaries-in-react-v16) |
| 56 | [How are error boundaries handled in React v15?](#how-are-error-boundaries-handled-in-react-v15) |
| 57 | [What are the recommended ways for static type checking?](#what-are-the-recommended-ways-for-static-type-checking) |
| 58 | [What is the use of react-dom package?](#what-is-the-use-of-react-dom-package) |
| 59 | [What is the purpose of render method of react-dom?](#what-is-the-purpose-of-render-method-of-react-dom) |
| 60 | [What is ReactDOMServer?](#what-is-reactdomserver) |
| 61 | [How to use InnerHtml in React?](#how-to-use-innerhtml-in-react) |
| 62 | [How to use styles in React?](#how-to-use-styles-in-react) |
| 63 | [How events are different in React?](#how-events-are-different-in-react) |
| 64 | [What will happen if you use setState in constructor?](#what-will-happen-if-you-use-setstate-in-constructor) |
| 65 | [What is the impact of indexes as keys?](#what-is-the-impact-of-indexes-as-keys) |
| 66 | [Is it good to use setState() in componentWillMount() method?](#is-it-good-to-use-setstate-in-componentwillmount-method) |
| 67 | [What will happen if you use props in initial state?](#what-will-happen-if-you-use-props-in-initial-state) |
| 68 | [How do you conditionally render components?](#how-do-you-conditionally-render-components) |
| 69 | [Why we need to be careful when spreading props on DOM elements??](#why-we-need-to-be-careful-when-spreading-props-on-dom-elements) |
| 70 | [How you use decorators in React?](#how-you-use-decorators-in-react) |
| 71 | [How do you memoize a component?](#how-do-you-memoize-a-component) |
| 72 | [How you implement Server-Side Rendering or SSR?](#how-you-implement-server-side-rendering-or-ssr) |
| 73 | [How to enable production mode in React?](#how-to-enable-production-mode-in-react) |
| 74 | [What is CRA and its benefits?](#what-is-cra-and-its-benefits) |
| 75 | [What is the lifecycle methods order in mounting?](#what-is-the-lifecycle-methods-order-in-mounting) |
| 76 | [What are the lifecycle methods going to be deprecated in React v16?](#what-are-the-lifecycle-methods-going-to-be-deprecated-in-react-v16) |
| 77 | [What is the purpose of getDerivedStateFromProps() lifecycle method?](#what-is-the-purpose-of-getderivedstatefromprops-lifecycle-method) |
| 78 | [What is the purpose of getSnapshotBeforeUpdate() lifecycle method?](#what-is-the-purpose-of-getsnapshotbeforeupdate-lifecycle-method) |
| 79 | [Do Hooks replace render props and higher order components?](#do-hooks-replace-render-props-and-higher-order-components) |
| 80 | [What is the recommended way for naming components?](#what-is-the-recommended-way-for-naming-components) |
| 81 | [What is the recommended ordering of methods in component class?](#what-is-the-recommended-ordering-of-methods-in-component-class) |
| 82 | [What is a switching component?](#what-is-a-switching-component) |
| 83 | [Why we need to pass a function to setState()?](#why-we-need-to-pass-a-function-to-setstate) |
| 84 | [What are React Mixins?](#what-are-react-mixins) |
| 85 | [Why is isMounted() an anti-pattern and what is the proper solution?](#why-is-ismounted-an-anti-pattern-and-what-is-the-proper-solution) |
| 86 | [What are the Pointer Events supported in React?](#what-are-the-pointer-events-supported-in-react) |
| 87 | [Why should component names start with capital letter?](#why-should-component-names-start-with-capital-letter) |
| 88 | [Are custom DOM attributes supported in React v16?](#are-custom-dom-attributes-supported-in-react-v16) |
| 89 | [What is the difference between constructor and getInitialState?](#what-is-the-difference-between-constructor-and-getinitialstate) |
| 90 | [Can you force a component to re-render without calling setState?](#can-you-force-a-component-to-re-render-without-calling-setstate) |
| 91 | [What is the difference between super() and super(props) in React using ES6 classes?](#what-is-the-difference-between-super-and-superprops-in-react-using-es6-classes) |
| 92 | [How to loop inside JSX?](#how-to-loop-inside-jsx) |
| 93 | [How do you access props in attribute quotes?](#how-do-you-access-props-in-attribute-quotes) |
| 94 | [What is React PropType array with shape?](#what-is-react-proptype-array-with-shape) |
| 95 | [How to conditionally apply class attributes?](#how-to-conditionally-apply-class-attributes) |
| 96 | [What is the difference between React and ReactDOM?](#what-is-the-difference-between-react-and-reactdom) |
| 97 | [Why ReactDOM is separated from React?](#why-reactdom-is-separated-from-react) |
| 98 | [How to use React label element?](#how-to-use-react-label-element) |
| 99 | [How to combine multiple inline style objects?](#how-to-combine-multiple-inline-style-objects) |
| 100 | [How to re-render the view when the browser is resized?](#how-to-re-render-the-view-when-the-browser-is-resized) |
| 101 | [What is the difference between setState and replaceState methods?](#what-is-the-difference-between-setstate-and-replacestate-methods) |
| 102 | [How to listen to state changes?](#how-to-listen-to-state-changes) |
| 103 | [What is the recommended approach of removing an array element in react state?](#what-is-the-recommended-approach-of-removing-an-array-element-in-react-state) |
| 104 | [Is it possible to use React without rendering HTML?](#is-it-possible-to-use-react-without-rendering-html) |
| 105 | [How to pretty print JSON with React?](#how-to-pretty-print-json-with-react) |
| 106 | [Why you can't update props in React?](#why-you-cant-update-props-in-react) |
| 107 | [How to focus an input element on page load?](#how-to-focus-an-input-element-on-page-load) |
| 108 | [What are the possible ways of updating objects in state?](#what-are-the-possible-ways-of-updating-objects-in-state) |
| 110 | [How can we find the version of React at runtime in the browser?](#how-can-we-find-the-version-of-react-at-runtime-in-the-browser) |
| 111 | [What are the approaches to include polyfills in your create-react-app?](#what-are-the-approaches-to-include-polyfills-in-your-create-react-app) |
| 112 | [How to use https instead of http in create-react-app?](#how-to-use-https-instead-of-http-in-create-react-app) |
| 113 | [How to avoid using relative path imports in create-react-app?](#how-to-avoid-using-relative-path-imports-in-create-react-app) |
| 114 | [How to add Google Analytics for react-router?](#how-to-add-google-analytics-for-react-router) |
| 115 | [How to update a component every second?](#how-to-update-a-component-every-second) |
| 116 | [How do you apply vendor prefixes to inline styles in React?](#how-do-you-apply-vendor-prefixes-to-inline-styles-in-react) |
| 117 | [How to import and export components using react and ES6?](#how-to-import-and-export-components-using-react-and-es6) |
| 118 | [What are the exceptions on React component naming?](#what-are-the-exceptions-on-react-component-naming) |
| 119 | [Why is a component constructor called only once?](#why-is-a-component-constructor-called-only-once) |
| 120 | [How to define constants in React?](#how-to-define-constants-in-react) |
| 121 | [How to programmatically trigger click event in React?](#how-to-programmatically-trigger-click-event-in-react) |
| 122 | [Is it possible to use async/await in plain React?](#is-it-possible-to-use-asyncawait-in-plain-react) |
| 123 | [What are the common folder structures for React?](#what-are-the-common-folder-structures-for-react) |
| 124 | [What are the popular packages for animation?](#what-are-the-popular-packages-for-animation) |
| 125 | [What is the benefit of styles modules?](#what-is-the-benefit-of-styles-modules) |
| 126 | [What are the popular React-specific linters?](#what-are-the-popular-react-specific-linters) |
| 127 | [How to make AJAX call and In which component lifecycle methods should I make an AJAX call?](#how-to-make-ajax-call-and-in-which-component-lifecycle-methods-should-i-make-an-ajax-call) |
| 128 | [What are render props?](#what-are-render-props) |
| | **React Router** |
| 129 | [What is React Router?](#what-is-react-router) |
| 130 | [How React Router is different from history library?](#how-react-router-is-different-from-history-library) |
| 131 | [What are the \<Router> components of React Router v4?](#what-are-the-router-components-of-react-router-v4) |
| 132 | [What is the purpose of push and replace methods of history?](#what-is-the-purpose-of-push-and-replace-methods-of-history) |
| 133 | [How do you programmatically navigate using React router v4?](#how-do-you-programmatically-navigate-using-react-router-v4) |
| 134 | [How to get query parameters in React Router v4](#how-to-get-query-parameters-in-react-router-v4) |
| 135 | [Why you get "Router may have only one child element" warning?](#why-you-get-router-may-have-only-one-child-element-warning) |
| 136 | [How to pass params to history.push method in React Router v4?](#how-to-pass-params-to-historypush-method-in-react-router-v4) |
| 137 | [How to implement default or NotFound page?](#how-to-implement-default-or-notfound-page) |
| 138 | [How to get history on React Router v4?](#how-to-get-history-on-react-router-v4) |
| 139 | [How to perform automatic redirect after login?](#how-to-perform-automatic-redirect-after-login) |
| | **React Internationalization** |
| 140 | [What is React-Intl?](#what-is-react-intl) |
| 141 | [What are the main features of React Intl?](#what-are-the-main-features-of-react-intl) |
| 142 | [What are the two ways of formatting in React Intl?](#what-are-the-two-ways-of-formatting-in-react-intl) |
| 143 | [How to use FormattedMessage as placeholder using React Intl?](#how-to-use-formattedmessage-as-placeholder-using-react-intl) |
| 144 | [How to access current locale with React Intl](#how-to-access-current-locale-with-react-intl) |
| 145 | [How to format date using React Intl?](#how-to-format-date-using-react-intl) |
| | **React Testing** |
| 146 | [What is Shallow Renderer in React testing?](#what-is-shallow-renderer-in-react-testing) |
| 147 | [What is TestRenderer package in React?](#what-is-testrenderer-package-in-react) |
| 148 | [What is the purpose of ReactTestUtils package?](#what-is-the-purpose-of-reacttestutils-package) |
| 149 | [What is Jest?](#what-is-jest) |
| 150 | [What are the advantages of Jest over Jasmine?](#what-are-the-advantages-of-jest-over-jasmine) |
| 151 | [Give a simple example of Jest test case](#give-a-simple-example-of-jest-test-case) |
| | **React Redux** |
| 152 | [What is Flux?](#what-is-flux) |
| 153 | [What is Redux?](#what-is-redux) |
| 154 | [What are the core principles of Redux?](#what-are-the-core-principles-of-redux) |
| 155 | [What are the downsides of Redux compared to Flux?](#what-are-the-downsides-of-redux-compared-to-flux) |
| 156 | [What is the difference between mapStateToProps() and mapDispatchToProps()?](#what-is-the-difference-between-mapstatetoprops-and-mapdispatchtoprops) |
| 157 | [Can I dispatch an action in reducer?](#can-i-dispatch-an-action-in-reducer) |
| 158 | [How to access Redux store outside a component?](#how-to-access-redux-store-outside-a-component) |
| 159 | [What are the drawbacks of MVW pattern](#what-are-the-drawbacks-of-mvw-pattern) |
| 160 | [Are there any similarities between Redux and RxJS?](#are-there-any-similarities-between-redux-and-rxjs) |
| 161 | [How to dispatch an action on load?](#how-to-dispatch-an-action-on-load) |
| 162 | [How to use connect from React Redux?](#how-to-use-connect-from-react-redux) |
| 163 | [How to reset state in Redux?](#how-to-reset-state-in-redux) |
| 164 | [Whats the purpose of at symbol in the redux connect decorator?](#whats-the-purpose-of-at-symbol-in-the-redux-connect-decorator) |
| 165 | [What is the difference between React context and React Redux?](#what-is-the-difference-between-react-context-and-react-redux) |
| 166 | [Why are Redux state functions called reducers?](#why-are-redux-state-functions-called-reducers) |
| 167 | [How to make AJAX request in Redux?](#how-to-make-ajax-request-in-redux) |
| 168 | [Should I keep all component's state in Redux store?](#should-i-keep-all-components-state-in-redux-store) |
| 169 | [What is the proper way to access Redux store?](#what-is-the-proper-way-to-access-redux-store) |
| 170 | [What is the difference between component and container in React Redux?](#what-is-the-difference-between-component-and-container-in-react-redux) |
| 171 | [What is the purpose of the constants in Redux? ](#what-is-the-purpose-of-the-constants-in-redux) |
| 172 | [What are the different ways to write mapDispatchToProps()?](#what-are-the-different-ways-to-write-mapdispatchtoprops) |
| 173 | [What is the use of the ownProps parameter in mapStateToProps() and mapDispatchToProps()?](#what-is-the-use-of-the-ownprops-parameter-in-mapstatetoprops-and-mapdispatchtoprops) |
| 174 | [How to structure Redux top level directories?](#how-to-structure-redux-top-level-directories) |
| 175 | [What is redux-saga?](#what-is-redux-saga) |
| 176 | [What is the mental model of redux-saga?](#what-is-the-mental-model-of-redux-saga) |
| 177 | [What are the differences between call and put in redux-saga](#what-are-the-differences-between-call-and-put-in-redux-saga) |
| 178 | [What is Redux Thunk?](#what-is-redux-thunk) |
| 179 | [What are the differences between redux-saga and redux-thunk](#what-are-the-differences-between-redux-saga-and-redux-thunk) |
| 180 | [What is Redux DevTools?](#what-is-redux-devtools) |
| 181 | [What are the features of Redux DevTools?](#what-are-the-features-of-redux-devtools) |
| 182 | [What are Redux selectors and Why to use them?](#what-are-redux-selectors-and-why-to-use-them) |
| 183 | [What is Redux Form?](#what-is-redux-form) |
| 184 | [What are the main features of Redux Form?](#what-are-the-main-features-of-redux-form) |
| 185 | [How to add multiple middlewares to Redux?](#how-to-add-multiple-middlewares-to-redux) |
| 186 | [How to set initial state in Redux?](#how-to-set-initial-state-in-redux) |
| 187 | [How Relay is different from Redux?](#how-relay-is-different-from-redux) |
| 188 | [What is an action in Redux?](#what-is-an-action-in-redux) |
| | **React Native** |
| 188 | [What is the difference between React Native and React?](#what-is-the-difference-between-react-native-and-react) |
| 189 | [How to test React Native apps?](#how-to-test-react-native-apps) |
| 190 | [How to do logging in React Native?](#how-to-do-logging-in-react-native) |
| 191 | [How to debug your React Native?](#how-to-debug-your-react-native) |
| | **React supported libraries and Integration** |
| 192 | [What is reselect and how it works?](#what-is-reselect-and-how-it-works) |
| 193 | [What is Flow?](#what-is-flow) |
| 194 | [What is the difference between Flow and PropTypes?](#what-is-the-difference-between-flow-and-proptypes) |
| 195 | [How to use font-awesome icons in React?](#how-to-use-font-awesome-icons-in-react) |
| 196 | [What is React Dev Tools?](#what-is-react-dev-tools) |
| 197 | [Why is DevTools not loading in Chrome for local files?](#why-is-devtools-not-loading-in-chrome-for-local-files) |
| 198 | [How to use Polymer in React?](#how-to-use-polymer-in-react) |
| 199 | [What are the advantages of React over Vue.js?](#what-are-the-advantages-of-react-over-vuejs) |
| 200 | [What is the difference between React and Angular?](#what-is-the-difference-between-react-and-angular) |
| 201 | [Why React tab is not showing up in DevTools?](#why-react-tab-is-not-showing-up-in-devtools) |
| 202 | [What are styled components?](#what-are-styled-components) |
| 203 | [Give an example of Styled Components?](#give-an-example-of-styled-components) |
| 204 | [What is Relay?](#what-is-relay) |
| 205 | [How to use TypeScript in create-react-app application?](#how-to-use-typescript-in-create-react-app-application) |
| | **Miscellaneous** |
| 206 | [What are the main features of reselect library?](#what-are-the-main-features-of-reselect-library) |
| 207 | [Give an example of reselect usage?](#give-an-example-of-reselect-usage) |
| 209 | [Does the statics object work with ES6 classes in React?](#does-the-statics-object-work-with-es6-classes-in-react) |
| 210 | [Can Redux only be used with React?](#can-redux-only-be-used-with-react) |
| 211 | [Do you need to have a particular build tool to use Redux?](#do-you-need-to-have-a-particular-build-tool-to-use-redux) |
| 212 | [How Redux Form initialValues get updated from state?](#how-redux-form-initialvalues-get-updated-from-state) |
| 213 | [How React PropTypes allow different type for one prop?](#how-react-proptypes-allow-different-types-for-one-prop) |
| 214 | [Can I import an SVG file as react component?](#can-i-import-an-svg-file-as-react-component) |
| 215 | [Why are inline ref callbacks or functions not recommended?](#why-are-inline-ref-callbacks-or-functions-not-recommended) |
| 216 | [What is render hijacking in React?](#what-is-render-hijacking-in-react) |
| 217 | [What are HOC factory implementations?](#what-are-hoc-factory-implementations) |
| 218 | [How to pass numbers to React component?](#how-to-pass-numbers-to-react-component) |
| 219 | [Do I need to keep all my state into Redux? Should I ever use react internal state?](#do-i-need-to-keep-all-my-state-into-redux-should-i-ever-use-react-internal-state) |
| 220 | [What is the purpose of registerServiceWorker in React?](#what-is-the-purpose-of-registerserviceworker-in-react) |
| 221 | [What is React memo function?](#what-is-react-memo-function) |
| 222 | [What is React lazy function?](#what-is-react-lazy-function) |
| 223 | [How to prevent unnecessary updates using setState?](#how-to-prevent-unnecessary-updates-using-setstate) |
| 224 | [How do you render Array, Strings and Numbers in React 16 Version?](#how-do-you-render-array-strings-and-numbers-in-react-16-version) |
| 225 | [How to use class field declarations syntax in React classes?](#how-to-use-class-field-declarations-syntax-in-react-classes) |
| 226 | [What are hooks?](#what-are-hooks) |
| 227 | [What rules need to be followed for hooks?](#what-rules-need-to-be-followed-for-hooks) |
| 228 | [How to ensure hooks followed the rules in your project?](#how-to-ensure-hooks-followed-the-rules-in-your-project) |
| 229 | [What are the differences between Flux and Redux?](#what-are-the-differences-between-flux-and-redux) |
| 230 | [What are the benefits of React Router V4?](#what-are-the-benefits-of-react-router-v4) |
| 231 | [Can you describe about componentDidCatch lifecycle method signature?](#can-you-describe-about-componentdidcatch-lifecycle-method-signature) |
| 232 | [In which scenarios error boundaries do not catch errors?](#in-which-scenarios-error-boundaries-do-not-catch-errors) |
| 233 | [Why do you not need error boundaries for event handlers?](#why-do-you-not-need-error-boundaries-for-event-handlers) |
| 234 | [What is the difference between try catch block and error boundaries?](#what-is-the-difference-between-try-catch-block-and-error-boundaries) |
| 235 | [What is the behavior of uncaught errors in react 16?](#what-is-the-behavior-of-uncaught-errors-in-react-16) |
| 236 | [What is the proper placement for error boundaries?](#what-is-the-proper-placement-for-error-boundaries) |
| 237 | [What is the benefit of component stack trace from error boundary?](#what-is-the-benefit-of-component-stack-trace-from-error-boundary) |
| 238 | [What is the required method to be defined for a class component?](#what-is-the-required-method-to-be-defined-for-a-class-component) |
| 239 | [What are the possible return types of render method?](#what-are-the-possible-return-types-of-render-method) |
| 240 | [What is the main purpose of constructor?](#what-is-the-main-purpose-of-constructor) |
| 241 | [Is it mandatory to define constructor for React component?](#is-it-mandatory-to-define-constructor-for-react-component) |
| 242 | [What are default props?](#what-are-default-props) |
| 243 | [Why should not call setState in componentWillUnmount?](#why-should-not-call-setstate-in-componentwillunmount) |
| 244 | [What is the purpose of getDerivedStateFromError?](#what-is-the-purpose-of-getderivedstatefromerror) |
| 245 | [What is the methods order when component re-rendered?](#what-is-the-methods-order-when-component-re-rendered) |
| 246 | [What are the methods invoked during error handling?](#what-are-the-methods-invoked-during-error-handling) |
| 247 | [What is the purpose of displayName class property?](#what-is-the-purpose-of-displayname-class-property) |
| 248 | [What is the browser support for react applications?](#what-is-the-browser-support-for-react-applications) |
| 249 | [What is the purpose of unmountComponentAtNode method?](#what-is-the-purpose-of-unmountcomponentatnode-method) |
| 250 | [What is code-splitting?](#what-is-code-splitting) |
| 251 | [What is the benefit of strict mode?](#what-is-the-benefit-of-strict-mode) |
| 252 | [What are Keyed Fragments?](#what-are-keyed-fragments) |
| 253 | [Does React support all HTML attributes?](#does-react-support-all-html-attributes) |
| 254 | [What are the limitations with HOCs?](#what-are-the-limitations-with-hocs) |
| 255 | [How to debug forwardRefs in DevTools?](#how-to-debug-forwardrefs-in-devtools) |
| 256 | [When component props defaults to true?](#when-component-props-defaults-to-true) |
| 257 | [What is NextJS and major features of it?](#what-is-nextjs-and-major-features-of-it) |
| 258 | [How do you pass an event handler to a component?](#how-do-you-pass-an-event-handler-to-a-component) |
| 259 | [Is it good to use arrow functions in render methods?](#is-it-good-to-use-arrow-functions-in-render-methods) |
| 260 | [How to prevent a function from being called multiple times?](#how-to-prevent-a-function-from-being-called-multiple-times) |
| 261 | [How JSX prevents Injection Attacks?](#how-jsx-prevents-injection-attacks) |
| 262 | [How do you update rendered elements?](#how-do-you-update-rendered-elements) |
| 263 | [How do you say that props are read only?](#how-do-you-say-that-props-are-read-only) |
| 264 | [How do you say that state updates are merged?](#how-do-you-say-that-state-updates-are-merged) |
| 265 | [How do you pass arguments to an event handler?](#how-do-you-pass-arguments-to-an-event-handler) |
| 266 | [How to prevent component from rendering?](#how-to-prevent-component-from-rendering) |
| 267 | [What are the conditions to safely use the index as a key?](#what-are-the-conditions-to-safely-use-the-index-as-a-key) |
| 268 | [Is it keys should be globally unique?](#is-it-keys-should-be-globally-unique) |
| 269 | [What is the popular choice for form handling?](#what-is-the-popular-choice-for-form-handling) |
| 270 | [What are the advantages of formik over redux form library?](#what-are-the-advantages-of-formik-over-redux-form-library) |
| 271 | [Why do you not required to use inheritance?](#why-do-you-not-required-to-use-inheritance) |
| 272 | [Can I use web components in react application?](#can-i-use-web-components-in-react-application) |
| 273 | [What is dynamic import?](#what-is-dynamic-import) |
| 274 | [What are loadable components?](#what-are-loadable-components) |
| 275 | [What is suspense component?](#what-is-suspense-component) |
| 276 | [What is route based code splitting?](#what-is-route-based-code-splitting) |
| 277 | [Give an example on How to use context?](#give-an-example-on-how-to-use-context) |
| 278 | [What is the purpose of default value in context?](#what-is-the-purpose-of-default-value-in-context) |
| 279 | [How do you use contextType?](#how-do-you-use-contexttype) |
| 280 | [What is a consumer?](#what-is-a-consumer) |
| 281 | [How do you solve performance corner cases while using context?](#how-do-you-solve-performance-corner-cases-while-using-context) |
| 282 | [What is the purpose of forward ref in HOCs?](#what-is-the-purpose-of-forward-ref-in-hocs) |
| 283 | [Is it ref argument available for all functions or class components?](#is-it-ref-argument-available-for-all-functions-or-class-components) |
| 284 | [Why do you need additional care for component libraries while using forward refs?](#why-do-you-need-additional-care-for-component-libraries-while-using-forward-refs) |
| 285 | [How to create react class components without ES6?](#how-to-create-react-class-components-without-es6) |
| 286 | [Is it possible to use react without JSX?](#is-it-possible-to-use-react-without-jsx) |
| 287 | [What is diffing algorithm?](#what-is-diffing-algorithm) |
| 288 | [What are the rules covered by diffing algorithm?](#what-are-the-rules-covered-by-diffing-algorithm) |
| 289 | [When do you need to use refs?](#when-do-you-need-to-use-refs) |
| 290 | [Is it prop must be named as render for render props?](#is-it-prop-must-be-named-as-render-for-render-props) |
| 291 | [What are the problems of using render props with pure components?](#what-are-the-problems-of-using-render-props-with-pure-components) |
| 292 | [How do you create HOC using render props?](#how-do-you-create-hoc-using-render-props) |
| 293 | [What is windowing technique?](#what-is-windowing-technique) |
| 294 | [How do you print falsy values in JSX?](#how-do-you-print-falsy-values-in-jsx) |
| 295 | [What is the typical use case of portals?](#what-is-the-typical-use-case-of-portals) |
| 296 | [How do you set default value for uncontrolled component?](#how-do-you-set-default-value-for-uncontrolled-component) |
| 297 | [What is your favorite React stack?](#what-is-your-favorite-react-stack) |
| 298 | [What is the difference between Real DOM and Virtual DOM?](#what-is-the-difference-between-real-dom-and-virtual-dom) |
| 299 | [How to add Bootstrap to a react application?](#how-to-add-bootstrap-to-a-react-application) |
| 300 | [Can you list down top websites or applications using react as front end framework?](#can-you-list-down-top-websites-or-applications-using-react-as-front-end-framework) |
| 301 | [Is it recommended to use CSS In JS technique in React?](#is-it-recommended-to-use-css-in-js-technique-in-react) |
| 302 | [Do I need to rewrite all my class components with hooks?](#do-i-need-to-rewrite-all-my-class-components-with-hooks) |
| 303 | [How to fetch data with React Hooks?](#how-to-fetch-data-with-react-hooks) |
| 304 | [Is Hooks cover all use cases for classes?](#is-hooks-cover-all-use-cases-for-classes) |
| 305 | [What is the stable release for hooks support?](#what-is-the-stable-release-for-hooks-support) |
| 306 | [Why do we use array destructuring (square brackets notation) in useState?](#why-do-we-use-array-destructuring-square-brackets-notation-in-usestate) |
| 307 | [What are the sources used for introducing hooks?](#what-are-the-sources-used-for-introducing-hooks) |
| 308 | [How do you access imperative API of web components?](#how-do-you-access-imperative-api-of-web-components) |
| 309 | [What is formik?](#what-is-formik) |
| 310 | [What are typical middleware choices for handling asynchronous calls in Redux?](#what-are-typical-middleware-choices-for-handling-asynchronous-calls-in-redux) |
| 311 | [Do browsers understand JSX code?](#do-browsers-understand-jsx-code) |
| 312 | [Describe about data flow in react?](#describe-about-data-flow-in-react) |
| 313 | [What is react scripts?](#what-is-react-scripts) |
| 314 | [What are the features of create react app?](#what-are-the-features-of-create-react-app) |
| 315 | [What is the purpose of renderToNodeStream method?](#what-is-the-purpose-of-rendertonodestream-method) |
| 316 | [What is MobX?](#what-is-mobx) |
| 317 | [What are the differences between Redux and MobX?](#what-are-the-differences-between-redux-and-mobx) |
| 318 | [Should I learn ES6 before learning ReactJS?](#should-i-learn-es6-before-learning-reactjs) |
| 319 | [What is Concurrent Rendering?](#what-is-concurrent-rendering) |
| 320 | [What is the difference between async mode and concurrent mode?](#what-is-the-difference-between-async-mode-and-concurrent-mode) |
| 321 | [Can I use javascript urls in react16.9?](#can-i-use-javascript-urls-in-react169) |
| 322 | [What is the purpose of eslint plugin for hooks?](#what-is-the-purpose-of-eslint-plugin-for-hooks) |
| 323 | [What is the difference between Imperative and Declarative in React?](#what-is-the-difference-between-imperative-and-declarative-in-react) |
| 324 | [What are the benefits of using typescript with reactjs?](#what-are-the-benefits-of-using-typescript-with-reactjs) |
| 325 | [How do you make sure that user remains authenticated on page refresh while using Context API State Management?](#how-do-you-make-sure-that-user-remains-authenticated-on-page-refresh-while-using-context-api-state-management) |
| 326 | [What are the benefits of new JSX transform?](#what-are-the-benefits-of-new-jsx-transform) |
| 327 | [How is the new JSX transform different from old transform?](#how-is-the-new-jsx-transform-different-from-old-transform) |
| 328 | [How do you get redux scaffolding using create-react-app?](#how-do-you-get-redux-scaffolding-using-create-react-app) |
| 329 | [What are React Server components?](#what-are-react-server-components) |
| 330 | [What is prop drilling?](#what-is-prop-drilling) |
| 331 | [What is state mutation and how to prevent it?](#what-is-state-mutation-and-how-to-prevent-it) |
| 332 | [What is the difference between useState and useRef hook?](#what-is-the-difference-between-usestate-and-useref-hook) |
| 333 | [What is a wrapper component ](#what-is-a-wrapper-component) |
| 334 | [What are the differences between useEffect and useLayoutEffect hooks](#what-are-the-differences-between-useEffect-and-useLayoutEffect-hooks) |
| 335 | [What are the differences between Functional and Class Components ](#what-are-the-differences-between-functional-and-class-components) |
| 336 | [What is strict mode in React?](#what-is-strict-mode-in-react) |
| 338 | [Why does strict mode render twice in React?](#why-does-strict-mode-render-twice-in-react) |
## Core React
1. ### What is React?
React (aka React.js or ReactJS) is an **open-source front-end JavaScript library** that is used for building composable user interfaces, especially for single-page applications. It is used for handling view layer for web and mobile apps based on components in a declarative approach.
React was created by [Jordan Walke](https://github.com/jordwalke), a software engineer working for Facebook. React was first deployed on Facebook's News Feed in 2011 and on Instagram in 2012.
**[⬆ Back to Top](#table-of-contents)**
2. ### What is the history behind React evolution?
The history of ReactJS started in 2010 with the creation of **XHP**. XHP is a PHP extension which improved the syntax of the language such that XML document fragments become valid PHP expressions and the primary purpose was used to create custom and reusable HTML elements.
The main principle of this extension was to make front-end code easier to understand and to help avoid cross-site scripting attacks. The project was successful to prevent the malicious content submitted by the scrubbing user.
But there was a different problem with XHP in which dynamic web applications require many roundtrips to the server, and XHP did not solve this problem. Also, the whole UI was re-rendered for small change in the application. Later, the initial prototype of React is created with the name **FaxJ** by Jordan inspired from XHP. Finally after sometime React has been introduced as a new library into JavaScript world.
**Note:** JSX comes from the idea of XHP
**[⬆ Back to Top](#table-of-contents)**
2. ### What are the major features of React?
The major features of React are:
- Uses **JSX** syntax, a syntax extension of JS that allows developers to write HTML in their JS code.
- It uses **Virtual DOM** instead of Real DOM considering that Real DOM manipulations are expensive.
- Supports **server-side rendering** which is useful for Search Engine Optimizations(SEO).
- Follows **Unidirectional or one-way** data flow or data binding.
- Uses **reusable/composable** UI components to develop the view.
**[⬆ Back to Top](#table-of-contents)**
3. ### What is JSX?
_JSX_ stands for _JavaScript XML_ and it is an XML-like syntax extension to ECMAScript. Basically it just provides the syntactic sugar for the `React.createElement(type, props, ...children)` function, giving us expressiveness of JavaScript along with HTML like template syntax.
In the example below, the text inside `<h1>` tag is returned as JavaScript function to the render function.
```jsx harmony
export default function App() {
return (
<h1 className="greeting">{"Hello, this is a JSX Code!"}</h1>
);
}
```
If you don't use JSX syntax then the respective JavaScript code should be written as below,
```javascript
import { createElement } from 'react';
export default function App() {
return createElement(
'h1',
{ className: 'greeting' },
'Hello, this is a JSX Code!'
);
}
```
<details><summary><b>See Class</b></summary>
<p>
```jsx harmony
class App extends React.Component {
render() {
return (
<h1 className="greeting">{"Hello, this is a JSX Code!"}</h1>
);
}
}
```
</p>
</details>
**Note:** JSX is stricter than HTML
**[⬆ Back to Top](#table-of-contents)**
4. ### What is the difference between Element and Component?
An _Element_ is a plain object describing what you want to appear on the screen in terms of the DOM nodes or other components. _Elements_ can contain other _Elements_ in their props. Creating a React element is cheap. Once an element is created, it cannot be mutated.
The JavaScript representation(Without JSX) of React Element would be as follows:
```javascript
const element = React.createElement("div", { id: "login-btn" }, "Login");
```
and this element can be simiplified using JSX
```html
<div id="login-btn">Login</div>
```
The above `React.createElement()` function returns an object as below:
```javascript
{
type: 'div',
props: {
children: 'Login',
id: 'login-btn'
}
}
```
Finally, this element renders to the DOM using `ReactDOM.render()`.
Whereas a **component** can be declared in several different ways. It can be a class with a `render()` method or it can be defined as a function. In either case, it takes props as an input, and returns a JSX tree as the output:
```javascript
const Button = ({ handleLogin }) => (
<div id={"login-btn"} onClick={handleLogin}>
Login
</div>
);
```
Then JSX gets transpiled to a `React.createElement()` function tree:
```javascript
const Button = ({ handleLogin }) =>
React.createElement(
"div",
{ id: "login-btn", onClick: handleLogin },
"Login"
);
```
**[⬆ Back to Top](#table-of-contents)**
5. ### How to create components in React?
Components are the building blocks of creating User Interfaces(UI) in React. There are two possible ways to create a component.
1. **Function Components:** This is the simplest way to create a component. Those are pure JavaScript functions that accept props object as the first parameter and return React elements to render the output:
```jsx harmony
function Greeting({ message }) {
return <h1>{`Hello, ${message}`}</h1>;
}
```
2. **Class Components:** You can also use ES6 class to define a component. The above function component can be written as a class component:
```jsx harmony
class Greeting extends React.Component {
render() {
return <h1>{`Hello, ${this.props.message}`}</h1>;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
6. ### When to use a Class Component over a Function Component?
After the addition of Hooks(i.e. React 16.8 onwards) it is always recommended to use Function components over Class components in React. Because you could use state, lifecycle methods and other features that were only available in class component present in function component too.
But even there are two reasons to use Class components over Function components.
1. If you need a React functionality whose Function component equivalent is not present yet, like Error Boundaries.
2. In older versions, If the component needs _state or lifecycle methods_ then you need to use class component.
**Note:** You can also use reusable [react error boundary](https://github.com/bvaughn/react-error-boundary) third-party component without writing any class. i.e, No need to use class components for Error boundaries.
The usage of Error boundaries from the above library is quite straight forward.
>**_Note when using react-error-boundary:_** ErrorBoundary is a client component. You can only pass props to it that are serializeable or use it in files that have a `"use client";` directive.
```jsx
"use client";
import { ErrorBoundary } from "react-error-boundary";
<ErrorBoundary fallback={<div>Something went wrong</div>}>
<ExampleApplication />
</ErrorBoundary>
```
**[⬆ Back to Top](#table-of-contents)**
7. ### What are Pure Components?
Pure components are the components which render the same output for the same state and props. In function components, you can achieve these pure components through memoized `React.memo()` API wrapping around the component. This API prevents unnecessary re-renders by comparing the previous props and new props using shallow comparison. So it will be helpful for performance optimizations.
But at the same time, it won't compare the previous state with the current state because function component itself prevents the unnecessary rendering by default when you set the same state again.
The syntactic representation of memoized components looks like below,
```jsx
const MemoizedComponent = memo(SomeComponent, arePropsEqual?);
```
Below is the example of how child component(i.e., EmployeeProfile) prevents re-renders for the same props passed by parent component(i.e.,EmployeeRegForm).
```jsx
import { memo, useState } from 'react';
const EmployeeProfile = memo(function EmployeeProfile({ name, email }) {
return (<>
<p>Name:{name}</p>
<p>Email: {email}</p>
</>);
});
export default function EmployeeRegForm() {
const [name, setName] = useState('');
const [email, setEmail] = useState('');
return (
<>
<label>
Name: <input value={name} onChange={e => setName(e.target.value)} />
</label>
<label>
Email: <input value={email} onChange={e => setEmail(e.target.value)} />
</label>
<hr/>
<EmployeeProfile name={name}/>
</>
);
}
```
In the above code, the email prop has not been passed to child component. So there won't be any re-renders for email prop change.
In class components, the components extending _`React.PureComponent`_ instead of _`React.Component`_ become the pure components. When props or state changes, _PureComponent_ will do a shallow comparison on both props and state by invoking `shouldComponentUpdate()` lifecycle method.
**Note:** `React.memo()` is a higher-order component.
**[⬆ Back to Top](#table-of-contents)**
8. ### What is state in React?
_State_ of a component is an object that holds some information that may change over the lifetime of the component. The important point is whenever the state object changes, the component re-renders. It is always recommended to make our state as simple as possible and minimize the number of stateful components.
Let's take an example of **User** component with message state. Here, **useState** hook has been used to add state to the User component and it returns an array with current state and function to update it.
```jsx harmony
import React, { useState } from "react";
function User() {
const [message, setMessage] = useState("Welcome to React world");
return (
<div>
<h1>{message}</h1>
</div>
);
}
```
<details><summary><b>See Class</b></summary>
<p>
```jsx harmony
import React from 'react';
class User extends React.Component {
constructor(props) {
super(props);
this.state = {
message: "Welcome to React world",
};
}
render() {
return (
<div>
<h1>{this.state.message}</h1>
</div>
);
}
}
```
</p>
</details>
State is similar to props, but it is private and fully controlled by the component ,i.e., it is not accessible to any other component till the owner component decides to pass it.
**[⬆ Back to Top](#table-of-contents)**
9. ### What are props in React?
_Props_ are inputs to components. They are single values or objects containing a set of values that are passed to components on creation similar to HTML-tag attributes. Here, the data is passed down from a parent component to a child component.
The primary purpose of props in React is to provide following component functionality:
1. Pass custom data to your component.
2. Trigger state changes.
3. Use via `this.props.reactProp` inside component's `render()` method.
For example, let us create an element with `reactProp` property:
```jsx harmony
<Element reactProp={"1"} />
```
This `reactProp` (or whatever you came up with) attribute name then becomes a property attached to React's native props object which originally already exists on all components created using React library.
```jsx harmony
props.reactProp
```
For example, the usage of props in function component looks like below:
```jsx
import React from "react";
import ReactDOM from "react-dom";
const ChildComponent = (props) => {
return (
<div>
<p>{props.name}</p>
<p>{props.age}</p>
</div>
);
};
const ParentComponent = () => {
return (
<div>
<ChildComponent name="John" age="30" />
<ChildComponent name="Mary" age="25" />
</div>
);
};
```
The properties from props object can be accessed directly using destructing feature from ES6 (ECMAScript 2015). The above child component can be simplified like below.
```jsx harmony
const ChildComponent = ({name, age}) => {
return (
<div>
<p>{name}</p>
<p>{age}</p>
</div>
);
};
```
<details><summary><b>See Class</b></summary>
The Props accessed in Class Based Component as below
```jsx
import React from "react";
import ReactDOM from "react-dom";
class ChildComponent extends React.Component {
render() {
return (
<div>
<p>{this.props.name}</p>
<p>{this.props.age}</p>
</div>
);
}
}
class ParentComponent extends React.Component {
render() {
return (
<div>
<ChildComponent name="John" age="30" />
<ChildComponent name="Mary" age="25" />
</div>
);
}
}
```
</details>
**[⬆ Back to Top](#table-of-contents)**
10. ### What is the difference between state and props?
In React, both `state` and `props` are plain JavaScript objects and used to manage the data of a component, but they are used in different ways and have different characteristics.
`state` is managed by the component itself and can be updated using the `setState()` function. Unlike props, state can be modified by the component and is used to manage the internal state of the component. Changes in the state trigger a re-render of the component and its children.
`props` (short for "properties") are passed to a component by its parent component and are `read-only`, meaning that they cannot be modified by the component itself. props can be used to configure the behavior of a component and to pass data between components.
**[⬆ Back to Top](#table-of-contents)**
11. ### Why should we not update the state directly?
If you try to update the state directly then it won't re-render the component.
```javascript
//Wrong
this.state.message = "Hello world";
```
Instead use `setState()` method. It schedules an update to a component's state object. When state changes, the component responds by re-rendering.
```javascript
//Correct
this.setState({ message: "Hello World" });
```
**Note:** You can directly assign to the state object either in _constructor_ or using latest javascript's class field declaration syntax.
**[⬆ Back to Top](#table-of-contents)**
12. ### What is the purpose of callback function as an argument of `setState()`?
The callback function is invoked when setState finished and the component gets rendered. Since `setState()` is **asynchronous** the callback function is used for any post action.
**Note:** It is recommended to use lifecycle method rather than this callback function.
```javascript
setState({ name: "John" }, () =>
console.log("The name has updated and component re-rendered")
);
```
**[⬆ Back to Top](#table-of-contents)**
13. ### What is the difference between HTML and React event handling?
Below are some of the main differences between HTML and React event handling,
1. In HTML, the event name usually represents in _lowercase_ as a convention:
```html
<button onclick="activateLasers()"></button>
```
Whereas in React it follows _camelCase_ convention:
```jsx harmony
<button onClick={activateLasers}>
```
2. In HTML, you can return `false` to prevent default behavior:
```html
<a
href="#"
onclick='console.log("The link was clicked."); return false;'
/>
```
Whereas in React you must call `preventDefault()` explicitly:
```javascript
function handleClick(event) {
event.preventDefault();
console.log("The link was clicked.");
}
```
3. In HTML, you need to invoke the function by appending `()`
Whereas in react you should not append `()` with the function name. (refer "activateLasers" function in the first point for example)
**[⬆ Back to Top](#table-of-contents)**
14. ### How to bind methods or event handlers in JSX callbacks?
There are 3 possible ways to achieve this in class components:
1. **Binding in Constructor:** In JavaScript classes, the methods are not bound by default. The same rule applies for React event handlers defined as class methods. Normally we bind them in constructor.
```javascript
class User extends Component {
constructor(props) {
super(props);
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
console.log("SingOut triggered");
}
render() {
return <button onClick={this.handleClick}>SingOut</button>;
}
}
```
2. **Public class fields syntax:** If you don't like to use bind approach then _public class fields syntax_ can be used to correctly bind callbacks. The Create React App enables this syntax by default.
```jsx harmony
handleClick = () => {
console.log("SingOut triggered", this);
};
```
```jsx harmony
<button onClick={this.handleClick}>SingOut</button>
```
3. **Arrow functions in callbacks:** It is possible to use _arrow functions_ directly in the callbacks.
```jsx harmony
handleClick() {
console.log('SingOut triggered');
}
render() {
return <button onClick={() => this.handleClick()}>SignOut</button>;
}
```
**Note:** If the callback is passed as prop to child components, those components might do an extra re-rendering. In those cases, it is preferred to go with `.bind()` or _public class fields syntax_ approach considering performance.
**[⬆ Back to Top](#table-of-contents)**
15. ### How to pass a parameter to an event handler or callback?
You can use an _arrow function_ to wrap around an _event handler_ and pass parameters:
```jsx harmony
<button onClick={() => this.handleClick(id)} />
```
This is an equivalent to calling `.bind`:
```jsx harmony
<button onClick={this.handleClick.bind(this, id)} />
```
Apart from these two approaches, you can also pass arguments to a function which is defined as arrow function
```jsx harmony
<button onClick={this.handleClick(id)} />;
handleClick = (id) => () => {
console.log("Hello, your ticket number is", id);
};
```
**[⬆ Back to Top](#table-of-contents)**
16. ### What are synthetic events in React?
`SyntheticEvent` is a cross-browser wrapper around the browser's native event. Its API is same as the browser's native event, including `stopPropagation()` and `preventDefault()`, except the events work identically across all browsers. The native events can be accessed directly from synthetic events using `nativeEvent` attribute.
Let's take an example of BookStore title search component with the ability to get all native event properties
```js
function BookStore() {
handleTitleChange(e) {
console.log('The new title is:', e.target.value);
// 'e' represents synthetic event
const nativeEvent = e.nativeEvent;
console.log(nativeEvent);
e.stopPropogation();
e.preventDefault();
}
return <input name="title" onChange={handleTitleChange} />
}
```
**[⬆ Back to Top](#table-of-contents)**
17. ### What are inline conditional expressions?
You can use either _if statements_ or _ternary expressions_ which are available from JS to conditionally render expressions. Apart from these approaches, you can also embed any expressions in JSX by wrapping them in curly braces and then followed by JS logical operator `&&`.
```jsx harmony
<h1>Hello!</h1>;
{
messages.length > 0 && !isLogin ? (
<h2>You have {messages.length} unread messages.</h2>
) : (
<h2>You don't have unread messages.</h2>
);
}
```
**[⬆ Back to Top](#table-of-contents)**
18. ### What is "key" prop and what is the benefit of using it in arrays of elements?
A `key` is a special attribute you **should** include when mapping over arrays to render data. _Key_ prop helps React identify which items have changed, are added, or are removed.
Keys should be unique among its siblings. Most often we use ID from our data as _key_:
```jsx harmony
const todoItems = todos.map((todo) => <li key={todo.id}>{todo.text}</li>);
```
When you don't have stable IDs for rendered items, you may use the item _index_ as a _key_ as a last resort:
```jsx harmony
const todoItems = todos.map((todo, index) => (
<li key={index}>{todo.text}</li>
));
```
**Note:**
1. Using _indexes_ for _keys_ is **not recommended** if the order of items may change. This can negatively impact performance and may cause issues with component state.
2. If you extract list item as separate component then apply _keys_ on list component instead of `li` tag.
3. There will be a warning message in the console if the `key` prop is not present on list items.
4. The key attribute accepts either string or number and internally convert it as string type.
**[⬆ Back to Top](#table-of-contents)**
19. ### What is the use of refs?
The _ref_ is used to return a reference to the element. They _should be avoided_ in most cases, however, they can be useful when you need a direct access to the DOM element or an instance of a component.
**[⬆ Back to Top](#table-of-contents)**
20. ### How to create refs?
There are two approaches
1. This is a recently added approach. _Refs_ are created using `React.createRef()` method and attached to React elements via the `ref` attribute. In order to use _refs_ throughout the component, just assign the _ref_ to the instance property within constructor.
```jsx harmony
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.myRef = React.createRef();
}
render() {
return <div ref={this.myRef} />;
}
}
```
2. You can also use ref callbacks approach regardless of React version. For example, the search bar component's input element is accessed as follows,
```jsx harmony
class SearchBar extends Component {
constructor(props) {
super(props);
this.txtSearch = null;
this.state = { term: "" };
this.setInputSearchRef = (e) => {
this.txtSearch = e;
};
}
onInputChange(event) {
this.setState({ term: this.txtSearch.value });
}
render() {
return (
<input
value={this.state.term}
onChange={this.onInputChange.bind(this)}
ref={this.setInputSearchRef}
/>
);
}
}
```
You can also use _refs_ in function components using **closures**.
**Note**: You can also use inline ref callbacks even though it is not a recommended approach.
**[⬆ Back to Top](#table-of-contents)**
21. ### What are forward refs?
_Ref forwarding_ is a feature that lets some components take a _ref_ they receive, and pass it further down to a child.
```jsx harmony
const ButtonElement = React.forwardRef((props, ref) => (
<button ref={ref} className="CustomButton">
{props.children}
</button>
));
// Create ref to the DOM button:
const ref = React.createRef();
<ButtonElement ref={ref}>{"Forward Ref"}</ButtonElement>;
```
**[⬆ Back to Top](#table-of-contents)**
22. ### Which is preferred option with in callback refs and findDOMNode()?
It is preferred to use _callback refs_ over `findDOMNode()` API. Because `findDOMNode()` prevents certain improvements in React in the future.
The **legacy** approach of using `findDOMNode`:
```javascript
class MyComponent extends Component {
componentDidMount() {
findDOMNode(this).scrollIntoView();
}
render() {
return <div />;
}
}
```
The recommended approach is:
```javascript
class MyComponent extends Component {
constructor(props) {
super(props);
this.node = createRef();
}
componentDidMount() {
this.node.current.scrollIntoView();
}
render() {
return <div ref={this.node} />;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
23. ### Why are String Refs legacy?
If you worked with React before, you might be familiar with an older API where the `ref` attribute is a string, like `ref={'textInput'}`, and the DOM node is accessed as `this.refs.textInput`. We advise against it because _string refs have below issues_, and are considered legacy. String refs were **removed in React v16**.
1. They _force React to keep track of currently executing component_. This is problematic because it makes react module stateful, and thus causes weird errors when react module is duplicated in the bundle.
2. They are _not composable_ — if a library puts a ref on the passed child, the user can't put another ref on it. Callback refs are perfectly composable.
3. They _don't work with static analysis_ like Flow. Flow can't guess the magic that framework does to make the string ref appear on `this.refs`, as well as its type (which could be different). Callback refs are friendlier to static analysis.
4. It doesn't work as most people would expect with the "render callback" pattern (e.g. <DataGrid renderRow={this.renderRow} />)
```jsx harmony
class MyComponent extends Component {
renderRow = (index) => {
// This won't work. Ref will get attached to DataTable rather than MyComponent:
return <input ref={"input-" + index} />;
// This would work though! Callback refs are awesome.
return <input ref={(input) => (this["input-" + index] = input)} />;
};
render() {
return (
<DataTable data={this.props.data} renderRow={this.renderRow} />
);
}
}
```
**[⬆ Back to Top](#table-of-contents)**
24. ### What is Virtual DOM?
The _Virtual DOM_ (VDOM) is an in-memory representation of _Real DOM_. The representation of a UI is kept in memory and synced with the "real" DOM. It's a step that happens between the render function being called and the displaying of elements on the screen. This entire process is called _reconciliation_.
**[⬆ Back to Top](#table-of-contents)**
25. ### How Virtual DOM works?
The _Virtual DOM_ works in three simple steps.
1. Whenever any underlying data changes, the entire UI is re-rendered in Virtual DOM representation.
2. Then the difference between the previous DOM representation and the new one is calculated.
3. Once the calculations are done, the real DOM will be updated with only the things that have actually changed.
**[⬆ Back to Top](#table-of-contents)**
26. ### What is the difference between Shadow DOM and Virtual DOM?
The _Shadow DOM_ is a browser technology designed primarily for scoping variables and CSS in _web components_. The _Virtual DOM_ is a concept implemented by libraries in JavaScript on top of browser APIs.
**[⬆ Back to Top](#table-of-contents)**
27. ### What is React Fiber?
Fiber is the new _reconciliation_ engine or reimplementation of core algorithm in React v16. The goal of React Fiber is to increase its suitability for areas like animation, layout, gestures, ability to pause, abort, or reuse work and assign priority to different types of updates; and new concurrency primitives.
**[⬆ Back to Top](#table-of-contents)**
28. ### What is the main goal of React Fiber?
The goal of _React Fiber_ is to increase its suitability for areas like animation, layout, and gestures. Its headline feature is **incremental rendering**: the ability to split rendering work into chunks and spread it out over multiple frames.
_from documentation_
Its main goals are:
1. Ability to split interruptible work in chunks.
2. Ability to prioritize, rebase and reuse work in progress.
3. Ability to yield back and forth between parents and children to support layout in React.
4. Ability to return multiple elements from render().
5. Better support for error boundaries.
**[⬆ Back to Top](#table-of-contents)**
29. ### What are controlled components?
A component that controls the input elements within the forms on subsequent user input is called **Controlled Component**, i.e, every state mutation will have an associated handler function.
For example, to write all the names in uppercase letters, we use handleChange as below,
```javascript
handleChange(event) {
this.setState({value: event.target.value.toUpperCase()})
}
```
**[⬆ Back to Top](#table-of-contents)**
30. ### What are uncontrolled components?
The **Uncontrolled Components** are the ones that store their own state internally, and you query the DOM using a ref to find its current value when you need it. This is a bit more like traditional HTML.
In the below UserProfile component, the `name` input is accessed using ref.
```jsx harmony
class UserProfile extends React.Component {
constructor(props) {
super(props);
this.handleSubmit = this.handleSubmit.bind(this);
this.input = React.createRef();
}
handleSubmit(event) {
alert("A name was submitted: " + this.input.current.value);
event.preventDefault();
}
render() {
return (
<form onSubmit={this.handleSubmit}>
<label>
{"Name:"}
<input type="text" ref={this.input} />
</label>
<input type="submit" value="Submit" />
</form>
);
}
}
```
In most cases, it's recommend to use controlled components to implement forms. In a controlled component, form data is handled by a React component. The alternative is uncontrolled components, where form data is handled by the DOM itself.
**[⬆ Back to Top](#table-of-contents)**
31. ### What is the difference between createElement and cloneElement?
JSX elements will be transpiled to `React.createElement()` functions to create React elements which are going to be used for the object representation of UI. Whereas `cloneElement` is used to clone an element and pass it new props.
**[⬆ Back to Top](#table-of-contents)**
32. ### What is Lifting State Up in React?
When several components need to share the same changing data then it is recommended to _lift the shared state up_ to their closest common ancestor. That means if two child components share the same data from its parent, then move the state to parent instead of maintaining local state in both of the child components.
**[⬆ Back to Top](#table-of-contents)**
33. ### What are the different phases of component lifecycle?
The component lifecycle has three distinct lifecycle phases:
1. **Mounting:** The component is ready to mount in the browser DOM. This phase covers initialization from `constructor()`, `getDerivedStateFromProps()`, `render()`, and `componentDidMount()` lifecycle methods.
2. **Updating:** In this phase, the component gets updated in two ways, sending the new props and updating the state either from `setState()` or `forceUpdate()`. This phase covers `getDerivedStateFromProps()`, `shouldComponentUpdate()`, `render()`, `getSnapshotBeforeUpdate()` and `componentDidUpdate()` lifecycle methods.
3. **Unmounting:** In this last phase, the component is not needed and gets unmounted from the browser DOM. This phase includes `componentWillUnmount()` lifecycle method.
It's worth mentioning that React internally has a concept of phases when applying changes to the DOM. They are separated as follows
1. **Render** The component will render without any side effects. This applies to Pure components and in this phase, React can pause, abort, or restart the render.
2. **Pre-commit** Before the component actually applies the changes to the DOM, there is a moment that allows React to read from the DOM through the `getSnapshotBeforeUpdate()`.
3. **Commit** React works with the DOM and executes the final lifecycles respectively `componentDidMount()` for mounting, `componentDidUpdate()` for updating, and `componentWillUnmount()` for unmounting.
React 16.3+ Phases (or an [interactive version](http://projects.wojtekmaj.pl/react-lifecycle-methods-diagram/))
Before React 16.3
**[⬆ Back to Top](#table-of-contents)**
34. ### What are the lifecycle methods of React?
Before React 16.3
- **componentWillMount:** Executed before rendering and is used for App level configuration in your root component.
- **componentDidMount:** Executed after first rendering and here all AJAX requests, DOM or state updates, and set up event listeners should occur.
- **componentWillReceiveProps:** Executed when particular prop updates to trigger state transitions.
- **shouldComponentUpdate:** Determines if the component will be updated or not. By default it returns `true`. If you are sure that the component doesn't need to render after state or props are updated, you can return false value. It is a great place to improve performance as it allows you to prevent a re-render if component receives new prop.
- **componentWillUpdate:** Executed before re-rendering the component when there are props & state changes confirmed by `shouldComponentUpdate()` which returns true.
- **componentDidUpdate:** Mostly it is used to update the DOM in response to prop or state changes.
- **componentWillUnmount:** It will be used to cancel any outgoing network requests, or remove all event listeners associated with the component.
React 16.3+
- **getDerivedStateFromProps:** Invoked right before calling `render()` and is invoked on _every_ render. This exists for rare use cases where you need a derived state. Worth reading [if you need derived state](https://reactjs.org/blog/2018/06/07/you-probably-dont-need-derived-state.html).
- **componentDidMount:** Executed after first rendering and where all AJAX requests, DOM or state updates, and set up event listeners should occur.
- **shouldComponentUpdate:** Determines if the component will be updated or not. By default, it returns `true`. If you are sure that the component doesn't need to render after the state or props are updated, you can return a false value. It is a great place to improve performance as it allows you to prevent a re-render if component receives a new prop.
- **getSnapshotBeforeUpdate:** Executed right before rendered output is committed to the DOM. Any value returned by this will be passed into `componentDidUpdate()`. This is useful to capture information from the DOM i.e. scroll position.
- **componentDidUpdate:** Mostly it is used to update the DOM in response to prop or state changes. This will not fire if `shouldComponentUpdate()` returns `false`.
- **componentWillUnmount** It will be used to cancel any outgoing network requests, or remove all event listeners associated with the component.
**[⬆ Back to Top](#table-of-contents)**
35. ### What are Higher-Order Components?
A _higher-order component_ (_HOC_) is a function that takes a component and returns a new component. Basically, it's a pattern that is derived from React's compositional nature.
We call them **pure components** because they can accept any dynamically provided child component but they won't modify or copy any behavior from their input components.
```javascript
const EnhancedComponent = higherOrderComponent(WrappedComponent);
```
HOC can be used for many use cases:
1. Code reuse, logic and bootstrap abstraction.
2. Render hijacking.
3. State abstraction and manipulation.
4. Props manipulation.
**[⬆ Back to Top](#table-of-contents)**
36. ### How to create props proxy for HOC component?
You can add/edit props passed to the component using _props proxy_ pattern like this:
```jsx harmony
function HOC(WrappedComponent) {
return class Test extends Component {
render() {
const newProps = {
title: "New Header",
footer: false,
showFeatureX: false,
showFeatureY: true,
};
return <WrappedComponent {...this.props} {...newProps} />;
}
};
}
```
**[⬆ Back to Top](#table-of-contents)**
37. ### What is context?
_Context_ provides a way to pass data through the component tree without having to pass props down manually at every level.
For example, authenticated users, locale preferences, UI themes need to be accessed in the application by many components.
```javascript
const { Provider, Consumer } = React.createContext(defaultValue);
```
**[⬆ Back to Top](#table-of-contents)**
38. ### What is children prop?
_Children_ is a prop (`this.props.children`) that allows you to pass components as data to other components, just like any other prop you use. Component tree put between component's opening and closing tag will be passed to that component as `children` prop.
There are several methods available in the React API to work with this prop. These include `React.Children.map`, `React.Children.forEach`, `React.Children.count`, `React.Children.only`, `React.Children.toArray`.
A simple usage of children prop looks as below,
```jsx harmony
const MyDiv = React.createClass({
render: function () {
return <div>{this.props.children}</div>;
},
});
ReactDOM.render(
<MyDiv>
<span>{"Hello"}</span>
<span>{"World"}</span>
</MyDiv>,
node
);
```
**[⬆ Back to Top](#table-of-contents)**
39. ### How to write comments in React?
The comments in React/JSX are similar to JavaScript Multiline comments but are wrapped in curly braces.
**Single-line comments:**
```jsx harmony
<div>
{/* Single-line comments(In vanilla JavaScript, the single-line comments are represented by double slash(//)) */}
{`Welcome ${user}, let's play React`}
</div>
```
**Multi-line comments:**
```jsx harmony
<div>
{/* Multi-line comments for more than
one line */}
{`Welcome ${user}, let's play React`}
</div>
```
**[⬆ Back to Top](#table-of-contents)**
40. ### What is the purpose of using super constructor with props argument?
A child class constructor cannot make use of `this` reference until the `super()` method has been called. The same applies to ES6 sub-classes as well. The main reason for passing props parameter to `super()` call is to access `this.props` in your child constructors.
**Passing props:**
```javascript
class MyComponent extends React.Component {
constructor(props) {
super(props);
console.log(this.props); // prints { name: 'John', age: 42 }
}
}
```
**Not passing props:**
```javascript
class MyComponent extends React.Component {
constructor(props) {
super();
console.log(this.props); // prints undefined
// but props parameter is still available
console.log(props); // prints { name: 'John', age: 42 }
}
render() {
// no difference outside constructor
console.log(this.props); // prints { name: 'John', age: 42 }
}
}
```
The above code snippets reveals that `this.props` is different only within the constructor. It would be the same outside the constructor.
**[⬆ Back to Top](#table-of-contents)**
41. ### What is reconciliation?
`Reconciliation` is the process through which React updates the Browser DOM and makes React work faster. React use a `diffing algorithm` so that component updates are predictable and faster. React would first calculate the difference between the `real DOM` and the copy of DOM `(Virtual DOM)` when there's an update of components.
React stores a copy of Browser DOM which is called `Virtual DOM`. When we make changes or add data, React creates a new Virtual DOM and compares it with the previous one. This comparison is done by `Diffing Algorithm`.
Now React compares the Virtual DOM with Real DOM. It finds out the changed nodes and updates only the changed nodes in Real DOM leaving the rest nodes as it is. This process is called _Reconciliation_.
**[⬆ Back to Top](#table-of-contents)**
42. ### How to set state with a dynamic key name?
If you are using ES6 or the Babel transpiler to transform your JSX code then you can accomplish this with _computed property names_.
```javascript
handleInputChange(event) {
this.setState({ [event.target.id]: event.target.value })
}
```
**[⬆ Back to Top](#table-of-contents)**
43. ### What would be the common mistake of function being called every time the component renders?
You need to make sure that function is not being called while passing the function as a parameter.
```jsx harmony
render() {
// Wrong: handleClick is called instead of passed as a reference!
return <button onClick={this.handleClick()}>{'Click Me'}</button>
}
```
Instead, pass the function itself without parenthesis:
```jsx harmony
render() {
// Correct: handleClick is passed as a reference!
return <button onClick={this.handleClick}>{'Click Me'}</button>
}
```
**[⬆ Back to Top](#table-of-contents)**
44. ### Is lazy function supports named exports?
No, currently `React.lazy` function supports default exports only. If you would like to import modules which are named exports, you can create an intermediate module that reexports it as the default. It also ensures that tree shaking keeps working and don’t pull unused components.
Let's take a component file which exports multiple named components,
```javascript
// MoreComponents.js
export const SomeComponent = /* ... */;
export const UnusedComponent = /* ... */;
```
and reexport `MoreComponents.js` components in an intermediate file `IntermediateComponent.js`
```javascript
// IntermediateComponent.js
export { SomeComponent as default } from "./MoreComponents.js";
```
Now you can import the module using lazy function as below,
```javascript
import React, { lazy } from "react";
const SomeComponent = lazy(() => import("./IntermediateComponent.js"));
```
**[⬆ Back to Top](#table-of-contents)**
45. ### Why React uses `className` over `class` attribute?
The attribute `class` is a keyword in JavaScript, and JSX is an extension of JavaScript. That's the principle reason why React uses `className` instead of `class`. Pass a string as the `className` prop.
```jsx harmony
render() {
return <span className={'menu navigation-menu'}>{'Menu'}</span>
}
```
**[⬆ Back to Top](#table-of-contents)**
46. ### What are fragments?
It's a common pattern or practice in React for a component to return multiple elements. _Fragments_ let you group a list of children without adding extra nodes to the DOM.
You need to use either **<Fragment>** or a shorter syntax having empty tag (**<></>**).
Below is the example of how to use fragment inside _Story_ component.
```jsx harmony
function Story({title, description, date}) {
return (
<Fragment>
<h2>{title}</h2>
<p>{description}</p>
<p>{date}</p>
</Fragment>
);
}
```
It is also possible to render list of fragments inside a loop with the mandatory **key** attribute supplied.
```jsx harmony
function StoryBook() {
return stories.map(story =>
<Fragment key={ story.id}>
<h2>{story.title}</h2>
<p>{story.description}</p>
<p>{story.date}</p>
</Fragment>
);
}
```
Usually, you don't need to use **<Fragment>** until unless there is a need of _key_ attribute. The usage of shorter syntax looks like below.
```jsx harmony
function Story({title, description, date}) {
return (
<>
<h2>{title}</h2>
<p>{description}</p>
<p>{date}</p>
</>
);
}
```
**[⬆ Back to Top](#table-of-contents)**
47. ### Why fragments are better than container divs?
Below are the list of reasons to prefer fragments over container DOM elements,
1. Fragments are a bit faster and use less memory by not creating an extra DOM node. This only has a real benefit on very large and deep trees.
2. Some CSS mechanisms like _Flexbox_ and _CSS Grid_ have a special parent-child relationships, and adding divs in the middle makes it hard to keep the desired layout.
3. The DOM Inspector is less cluttered.
**[⬆ Back to Top](#table-of-contents)**
48. ### What are portals in React?
_Portal_ is a recommended way to render children into a DOM node that exists outside the DOM hierarchy of the parent component.
```javascript
ReactDOM.createPortal(child, container);
```
The first argument is any render-able React child, such as an element, string, or fragment. The second argument is a DOM element.
**[⬆ Back to Top](#table-of-contents)**
49. ### What are stateless components?
If the behaviour of a component is independent of its state then it can be a stateless component. You can use either a function or a class for creating stateless components. But unless you need to use a lifecycle hook in your components, you should go for function components. There are a lot of benefits if you decide to use function components here; they are easy to write, understand, and test, a little faster, and you can avoid the `this` keyword altogether.
**[⬆ Back to Top](#table-of-contents)**
50. ### What are stateful components?
If the behaviour of a component is dependent on the _state_ of the component then it can be termed as stateful component. These _stateful components_ are either function components with hooks or _class components_.
Let's take an example of function stateful component which update the state based on click event,
```javascript
import React, {useState} from 'react';
const App = (props) => {
const [count, setCount] = useState(0);
handleIncrement() {
setCount(count+1);
}
return (
<>
<button onClick={handleIncrement}>Increment</button>
<span>Counter: {count}</span>
</>
)
}
```
<details><summary><b>See Class</b></summary>
<p>
The equivalent class stateful component with a state that gets initialized in the `constructor`.
```jsx harmony
class App extends Component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
handleIncrement() {
setState({count: this.state.count + 1})
}
render() {
<>
<button onClick={() => this.handleIncrement}>Increment</button>
<span>Count: {count}</span>
</>
}
}
```
</p>
</details>
**[⬆ Back to Top](#table-of-contents)**
51. ### How to apply validation on props in React?
When the application is running in _development mode_, React will automatically check all props that we set on components to make sure they have _correct type_. If the type is incorrect, React will generate warning messages in the console. It's disabled in _production mode_ due to performance impact. The mandatory props are defined with `isRequired`.
The set of predefined prop types:
1. `PropTypes.number`
2. `PropTypes.string`
3. `PropTypes.array`
4. `PropTypes.object`
5. `PropTypes.func`
6. `PropTypes.node`
7. `PropTypes.element`
8. `PropTypes.bool`
9. `PropTypes.symbol`
10. `PropTypes.any`
We can define `propTypes` for `User` component as below:
```jsx harmony
import React from "react";
import PropTypes from "prop-types";
class User extends React.Component {
static propTypes = {
name: PropTypes.string.isRequired,
age: PropTypes.number.isRequired,
};
render() {
return (
<>
<h1>{`Welcome, ${this.props.name}`}</h1>
<h2>{`Age, ${this.props.age}`}</h2>
</>
);
}
}
```
**Note:** In React v15.5 _PropTypes_ were moved from `React.PropTypes` to `prop-types` library.
_The Equivalent Functional Component_
```jsx harmony
import React from "react";
import PropTypes from "prop-types";
function User({ name, age }) {
return (
<>
<h1>{`Welcome, ${name}`}</h1>
<h2>{`Age, ${age}`}</h2>
</>
);
}
User.propTypes = {
name: PropTypes.string.isRequired,
age: PropTypes.number.isRequired,
};
```
**[⬆ Back to Top](#table-of-contents)**
52. ### What are the advantages of React?
Below are the list of main advantages of React,
1. Increases the application's performance with _Virtual DOM_.
2. JSX makes code easy to read and write.
3. It renders both on client and server side (_SSR_).
4. Easy to integrate with frameworks (Angular, Backbone) since it is only a view library.
5. Easy to write unit and integration tests with tools such as Jest.
**[⬆ Back to Top](#table-of-contents)**
53. ### What are the limitations of React?
Apart from the advantages, there are few limitations of React too,
1. React is just a view library, not a full framework.
2. There is a learning curve for beginners who are new to web development.
3. Integrating React into a traditional MVC framework requires some additional configuration.
4. The code complexity increases with inline templating and JSX.
5. Too many smaller components leading to over engineering or boilerplate.
**[⬆ Back to Top](#table-of-contents)**
54. ### What are error boundaries in React v16?
_Error boundaries_ are components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of the component tree that crashed.
A class component becomes an error boundary if it defines a new lifecycle method called `componentDidCatch(error, info)` or `static getDerivedStateFromError() `:
```jsx harmony
class ErrorBoundary extends React.Component {
constructor(props) {
super(props);
this.state = { hasError: false };
}
componentDidCatch(error, info) {
// You can also log the error to an error reporting service
logErrorToMyService(error, info);
}
static getDerivedStateFromError(error) {
// Update state so the next render will show the fallback UI.
return { hasError: true };
}
render() {
if (this.state.hasError) {
// You can render any custom fallback UI
return <h1>{"Something went wrong."}</h1>;
}
return this.props.children;
}
}
```
After that use it as a regular component:
```jsx harmony
<ErrorBoundary>
<MyWidget />
</ErrorBoundary>
```
**[⬆ Back to Top](#table-of-contents)**
55. ### How are error boundaries handled in React v15?
React v15 provided very basic support for _error boundaries_ using `unstable_handleError` method. It has been renamed to `componentDidCatch` in React v16.
**[⬆ Back to Top](#table-of-contents)**
56. ### What are the recommended ways for static type checking?
Normally we use _PropTypes library_ (`React.PropTypes` moved to a `prop-types` package since React v15.5) for _type checking_ in the React applications. For large code bases, it is recommended to use _static type checkers_ such as Flow or TypeScript, that perform type checking at compile time and provide auto-completion features.
**[⬆ Back to Top](#table-of-contents)**
57. ### What is the use of `react-dom` package?
The `react-dom` package provides _DOM-specific methods_ that can be used at the top level of your app. Most of the components are not required to use this module. Some of the methods of this package are:
1. `render()`
2. `hydrate()`
3. `unmountComponentAtNode()`
4. `findDOMNode()`
5. `createPortal()`
**[⬆ Back to Top](#table-of-contents)**
58. ### What is the purpose of render method of `react-dom`?
This method is used to render a React element into the DOM in the supplied container and return a reference to the component. If the React element was previously rendered into container, it will perform an update on it and only mutate the DOM as necessary to reflect the latest changes.
```
ReactDOM.render(element, container, [callback])
```
If the optional callback is provided, it will be executed after the component is rendered or updated.
**[⬆ Back to Top](#table-of-contents)**
59. ### What is ReactDOMServer?
The `ReactDOMServer` object enables you to render components to static markup (typically used on node server). This object is mainly used for _server-side rendering_ (SSR). The following methods can be used in both the server and browser environments:
1. `renderToString()`
2. `renderToStaticMarkup()`
For example, you generally run a Node-based web server like Express, Hapi, or Koa, and you call `renderToString` to render your root component to a string, which you then send as response.
```javascript
// using Express
import { renderToString } from "react-dom/server";
import MyPage from "./MyPage";
app.get("/", (req, res) => {
res.write(
"<!DOCTYPE html><html><head><title>My Page</title></head><body>"
);
res.write('<div id="content">');
res.write(renderToString(<MyPage />));
res.write("</div></body></html>");
res.end();
});
```
**[⬆ Back to Top](#table-of-contents)**
60. ### How to use innerHTML in React?
The `dangerouslySetInnerHTML` attribute is React's replacement for using `innerHTML` in the browser DOM. Just like `innerHTML`, it is risky to use this attribute considering cross-site scripting (XSS) attacks. You just need to pass a `__html` object as key and HTML text as value.
In this example MyComponent uses `dangerouslySetInnerHTML` attribute for setting HTML markup:
```jsx harmony
function createMarkup() {
return { __html: "First · Second" };
}
function MyComponent() {
return <div dangerouslySetInnerHTML={createMarkup()} />;
}
```
**[⬆ Back to Top](#table-of-contents)**
61. ### How to use styles in React?
The `style` attribute accepts a JavaScript object with camelCased properties rather than a CSS string. This is consistent with the DOM style JavaScript property, is more efficient, and prevents XSS security holes.
```jsx harmony
const divStyle = {
color: "blue",
backgroundImage: "url(" + imgUrl + ")",
};
function HelloWorldComponent() {
return <div style={divStyle}>Hello World!</div>;
}
```
Style keys are camelCased in order to be consistent with accessing the properties on DOM nodes in JavaScript (e.g. `node.style.backgroundImage`).
**[⬆ Back to Top](#table-of-contents)**
62. ### How events are different in React?
Handling events in React elements has some syntactic differences:
1. React event handlers are named using camelCase, rather than lowercase.
2. With JSX you pass a function as the event handler, rather than a string.
**[⬆ Back to Top](#table-of-contents)**
63. ### What will happen if you use `setState()` in constructor?
When you use `setState()`, then apart from assigning to the object state React also re-renders the component and all its children. You would get error like this: _Can only update a mounted or mounting component._ So we need to use `this.state` to initialize variables inside constructor.
**[⬆ Back to Top](#table-of-contents)**
64. ### What is the impact of indexes as keys?
Keys should be stable, predictable, and unique so that React can keep track of elements.
In the below code snippet each element's key will be based on ordering, rather than tied to the data that is being represented. This limits the optimizations that React can do.
```jsx harmony
{
todos.map((todo, index) => <Todo {...todo} key={index} />);
}
```
If you use element data for unique key, assuming todo.id is unique to this list and stable, React would be able to reorder elements without needing to reevaluate them as much.
```jsx harmony
{
todos.map((todo) => <Todo {...todo} key={todo.id} />);
}
```
**[⬆ Back to Top](#table-of-contents)**
65. ### Is it good to use `setState()` in `componentWillMount()` method?
Yes, it is safe to use `setState()` inside `componentWillMount()` method. But at the same it is recommended to avoid async initialization in `componentWillMount()` lifecycle method. `componentWillMount()` is invoked immediately before mounting occurs. It is called before `render()`, therefore setting state in this method will not trigger a re-render. Avoid introducing any side-effects or subscriptions in this method. We need to make sure async calls for component initialization happened in `componentDidMount()` instead of `componentWillMount()`.
```jsx harmony
componentDidMount() {
axios.get(`api/todos`)
.then((result) => {
this.setState({
messages: [...result.data]
})
})
}
```
**[⬆ Back to Top](#table-of-contents)**
66. ### What will happen if you use props in initial state?
If the props on the component are changed without the component being refreshed, the new prop value will never be displayed because the constructor function will never update the current state of the component. The initialization of state from props only runs when the component is first created.
The below component won't display the updated input value:
```jsx harmony
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
records: [],
inputValue: this.props.inputValue,
};
}
render() {
return <div>{this.state.inputValue}</div>;
}
}
```
Using props inside render method will update the value:
```jsx harmony
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
record: [],
};
}
render() {
return <div>{this.props.inputValue}</div>;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
67. ### How do you conditionally render components?
In some cases you want to render different components depending on some state. JSX does not render `false` or `undefined`, so you can use conditional _short-circuiting_ to render a given part of your component only if a certain condition is true.
```jsx harmony
const MyComponent = ({ name, address }) => (
<div>
<h2>{name}</h2>
{address && <p>{address}</p>}
</div>
);
```
If you need an `if-else` condition then use _ternary operator_.
```jsx harmony
const MyComponent = ({ name, address }) => (
<div>
<h2>{name}</h2>
{address ? <p>{address}</p> : <p>{"Address is not available"}</p>}
</div>
);
```
**[⬆ Back to Top](#table-of-contents)**
68. ### Why we need to be careful when spreading props on DOM elements?
When we _spread props_ we run into the risk of adding unknown HTML attributes, which is a bad practice. Instead we can use prop destructuring with `...rest` operator, so it will add only required props.
For example,
```jsx harmony
const ComponentA = () => (
<ComponentB isDisplay={true} className={"componentStyle"} />
);
const ComponentB = ({ isDisplay, ...domProps }) => (
<div {...domProps}>{"ComponentB"}</div>
);
```
**[⬆ Back to Top](#table-of-contents)**
69. ### How you use decorators in React?
You can _decorate_ your _class_ components, which is the same as passing the component into a function. **Decorators** are flexible and readable way of modifying component functionality.
```jsx harmony
@setTitle("Profile")
class Profile extends React.Component {
//....
}
/*
title is a string that will be set as a document title
WrappedComponent is what our decorator will receive when
put directly above a component class as seen in the example above
*/
const setTitle = (title) => (WrappedComponent) => {
return class extends React.Component {
componentDidMount() {
document.title = title;
}
render() {
return <WrappedComponent {...this.props} />;
}
};
};
```
**Note:** Decorators are a feature that didn't make it into ES7, but are currently a _stage 2 proposal_.
**[⬆ Back to Top](#table-of-contents)**
70. ### How do you memoize a component?
There are memoize libraries available which can be used on function components.
For example `moize` library can memoize the component in another component.
```jsx harmony
import moize from "moize";
import Component from "./components/Component"; // this module exports a non-memoized component
const MemoizedFoo = moize.react(Component);
const Consumer = () => {
<div>
{"I will memoize the following entry:"}
<MemoizedFoo />
</div>;
};
```
**Update:** Since React v16.6.0, we have a `React.memo`. It provides a higher order component which memoizes component unless the props change. To use it, simply wrap the component using React.memo before you use it.
```js
const MemoComponent = React.memo(function MemoComponent(props) {
/* render using props */
});
OR;
export default React.memo(MyFunctionComponent);
```
**[⬆ Back to Top](#table-of-contents)**
71. ### How you implement Server Side Rendering or SSR?
React is already equipped to handle rendering on Node servers. A special version of the DOM renderer is available, which follows the same pattern as on the client side.
```jsx harmony
import ReactDOMServer from "react-dom/server";
import App from "./App";
ReactDOMServer.renderToString(<App />);
```
This method will output the regular HTML as a string, which can be then placed inside a page body as part of the server response. On the client side, React detects the pre-rendered content and seamlessly picks up where it left off.
**[⬆ Back to Top](#table-of-contents)**
72. ### How to enable production mode in React?
You should use Webpack's `DefinePlugin` method to set `NODE_ENV` to `production`, by which it strip out things like propType validation and extra warnings. Apart from this, if you minify the code, for example, Uglify's dead-code elimination to strip out development only code and comments, it will drastically reduce the size of your bundle.
**[⬆ Back to Top](#table-of-contents)**
73. ### What is CRA and its benefits?
The `create-react-app` CLI tool allows you to quickly create & run React applications with no configuration step.
Let's create Todo App using _CRA_:
```console
# Installation
$ npm install -g create-react-app
# Create new project
$ create-react-app todo-app
$ cd todo-app
# Build, test and run
$ npm run build
$ npm run test
$ npm start
```
It includes everything we need to build a React app:
1. React, JSX, ES6, and Flow syntax support.
2. Language extras beyond ES6 like the object spread operator.
3. Autoprefixed CSS, so you don’t need -webkit- or other prefixes.
4. A fast interactive unit test runner with built-in support for coverage reporting.
5. A live development server that warns about common mistakes.
6. A build script to bundle JS, CSS, and images for production, with hashes and sourcemaps.
**[⬆ Back to Top](#table-of-contents)**
74. ### What is the lifecycle methods order in mounting?
The lifecycle methods are called in the following order when an instance of a component is being created and inserted into the DOM.
1. `constructor()`
2. `static getDerivedStateFromProps()`
3. `render()`
4. `componentDidMount()`
**[⬆ Back to Top](#table-of-contents)**
75. ### What are the lifecycle methods going to be deprecated in React v16?
The following lifecycle methods going to be unsafe coding practices and will be more problematic with async rendering.
1. `componentWillMount()`
2. `componentWillReceiveProps()`
3. `componentWillUpdate()`
Starting with React v16.3 these methods are aliased with `UNSAFE_` prefix, and the unprefixed version will be removed in React v17.
**[⬆ Back to Top](#table-of-contents)**
76. ### What is the purpose of `getDerivedStateFromProps()` lifecycle method?
The new static `getDerivedStateFromProps()` lifecycle method is invoked after a component is instantiated as well as before it is re-rendered. It can return an object to update state, or `null` to indicate that the new props do not require any state updates.
```javascript
class MyComponent extends React.Component {
static getDerivedStateFromProps(props, state) {
// ...
}
}
```
This lifecycle method along with `componentDidUpdate()` covers all the use cases of `componentWillReceiveProps()`.
**[⬆ Back to Top](#table-of-contents)**
77. ### What is the purpose of `getSnapshotBeforeUpdate()` lifecycle method?
The new `getSnapshotBeforeUpdate()` lifecycle method is called right before DOM updates. The return value from this method will be passed as the third parameter to `componentDidUpdate()`.
```javascript
class MyComponent extends React.Component {
getSnapshotBeforeUpdate(prevProps, prevState) {
// ...
}
}
```
This lifecycle method along with `componentDidUpdate()` covers all the use cases of `componentWillUpdate()`.
**[⬆ Back to Top](#table-of-contents)**
78. ### Do Hooks replace render props and higher order components?
Both render props and higher-order components render only a single child but in most of the cases Hooks are a simpler way to serve this by reducing nesting in your tree.
**[⬆ Back to Top](#table-of-contents)**
79. ### What is the recommended way for naming components?
It is recommended to name the component by reference instead of using `displayName`.
Using `displayName` for naming component:
```javascript
export default React.createClass({
displayName: "TodoApp",
// ...
});
```
The **recommended** approach:
```javascript
export default class TodoApp extends React.Component {
// ...
}
```
also
```javascript
const TodoApp = () => {
//...
};
export default TodoApp;
```
**[⬆ Back to Top](#table-of-contents)**
80. ### What is the recommended ordering of methods in component class?
_Recommended_ ordering of methods from _mounting_ to _render stage_:
1. `static` methods
2. `constructor()`
3. `getChildContext()`
4. `componentWillMount()`
5. `componentDidMount()`
6. `componentWillReceiveProps()`
7. `shouldComponentUpdate()`
8. `componentWillUpdate()`
9. `componentDidUpdate()`
10. `componentWillUnmount()`
11. click handlers or event handlers like `onClickSubmit()` or `onChangeDescription()`
12. getter methods for render like `getSelectReason()` or `getFooterContent()`
13. optional render methods like `renderNavigation()` or `renderProfilePicture()`
14. `render()`
**[⬆ Back to Top](#table-of-contents)**
81. ### What is a switching component?
A _switching component_ is a component that renders one of many components. We need to use object to map prop values to components.
For example, a switching component to display different pages based on `page` prop:
```jsx harmony
import HomePage from "./HomePage";
import AboutPage from "./AboutPage";
import ServicesPage from "./ServicesPage";
import ContactPage from "./ContactPage";
const PAGES = {
home: HomePage,
about: AboutPage,
services: ServicesPage,
contact: ContactPage,
};
const Page = (props) => {
const Handler = PAGES[props.page] || ContactPage;
return <Handler {...props} />;
};
// The keys of the PAGES object can be used in the prop types to catch dev-time errors.
Page.propTypes = {
page: PropTypes.oneOf(Object.keys(PAGES)).isRequired,
};
```
**[⬆ Back to Top](#table-of-contents)**
82. ### Why we need to pass a function to setState()?
The reason behind for this is that `setState()` is an asynchronous operation. React batches state changes for performance reasons, so the state may not change immediately after `setState()` is called. That means you should not rely on the current state when calling `setState()` since you can't be sure what that state will be. The solution is to pass a function to `setState()`, with the previous state as an argument. By doing this you can avoid issues with the user getting the old state value on access due to the asynchronous nature of `setState()`.
Let's say the initial count value is zero. After three consecutive increment operations, the value is going to be incremented only by one.
```javascript
// assuming this.state.count === 0
this.setState({ count: this.state.count + 1 });
this.setState({ count: this.state.count + 1 });
this.setState({ count: this.state.count + 1 });
// this.state.count === 1, not 3
```
If we pass a function to `setState()`, the count gets incremented correctly.
```javascript
this.setState((prevState, props) => ({
count: prevState.count + props.increment,
}));
// this.state.count === 3 as expected
```
**(OR)**
### Why function is preferred over object for `setState()`?
React may batch multiple `setState()` calls into a single update for performance. Because `this.props` and `this.state` may be updated asynchronously, you should not rely on their values for calculating the next state.
This counter example will fail to update as expected:
```javascript
// Wrong
this.setState({
counter: this.state.counter + this.props.increment,
});
```
The preferred approach is to call `setState()` with function rather than object. That function will receive the previous state as the first argument, and the props at the time the update is applied as the second argument.
```javascript
// Correct
this.setState((prevState, props) => ({
counter: prevState.counter + props.increment,
}));
```
**[⬆ Back to Top](#table-of-contents)**
84. ### What are React Mixins?
_Mixins_ are a way to totally separate components to have a common functionality. Mixins **should not be used** and can be replaced with _higher-order components_ or _decorators_.
One of the most commonly used mixins is `PureRenderMixin`. You might be using it in some components to prevent unnecessary re-renders when the props and state are shallowly equal to the previous props and state:
```javascript
const PureRenderMixin = require("react-addons-pure-render-mixin");
const Button = React.createClass({
mixins: [PureRenderMixin],
// ...
});
```
<!-- TODO: mixins are deprecated -->
**[⬆ Back to Top](#table-of-contents)**
85. ### Why is `isMounted()` an anti-pattern and what is the proper solution?
The primary use case for `isMounted()` is to avoid calling `setState()` after a component has been unmounted, because it will emit a warning.
```javascript
if (this.isMounted()) {
this.setState({...})
}
```
Checking `isMounted()` before calling `setState()` does eliminate the warning, but it also defeats the purpose of the warning. Using `isMounted()` is a code smell because the only reason you would check is because you think you might be holding a reference after the component has unmounted.
An optimal solution would be to find places where `setState()` might be called after a component has unmounted, and fix them. Such situations most commonly occur due to callbacks, when a component is waiting for some data and gets unmounted before the data arrives. Ideally, any callbacks should be canceled in `componentWillUnmount()`, prior to unmounting.
**[⬆ Back to Top](#table-of-contents)**
86. ### What are the Pointer Events supported in React?
_Pointer Events_ provide a unified way of handling all input events. In the old days we had a mouse and respective event listeners to handle them but nowadays we have many devices which don't correlate to having a mouse, like phones with touch surface or pens. We need to remember that these events will only work in browsers that support the _Pointer Events_ specification.
The following event types are now available in _React DOM_:
1. `onPointerDown`
2. `onPointerMove`
3. `onPointerUp`
4. `onPointerCancel`
5. `onGotPointerCapture`
6. `onLostPointerCapture`
7. `onPointerEnter`
8. `onPointerLeave`
9. `onPointerOver`
10. `onPointerOut`
**[⬆ Back to Top](#table-of-contents)**
87. ### Why should component names start with capital letter?
If you are rendering your component using JSX, the name of that component has to begin with a capital letter otherwise React will throw an error as an unrecognized tag. This convention is because only HTML elements and SVG tags can begin with a lowercase letter.
```jsx harmony
class SomeComponent extends Component {
// Code goes here
}
```
You can define component class which name starts with lowercase letter, but when it's imported it should have capital letter. Here lowercase is fine:
```jsx harmony
class myComponent extends Component {
render() {
return <div />;
}
}
export default myComponent;
```
While when imported in another file it should start with capital letter:
```jsx harmony
import MyComponent from "./myComponent";
```
#### What are the exceptions on React component naming?
The component names should start with an uppercase letter but there are few exceptions to this convention. The lowercase tag names with a dot (property accessors) are still considered as valid component names.
For example, the below tag can be compiled to a valid component,
```jsx harmony
render() {
return (
<obj.component/> // `React.createElement(obj.component)`
)
}
```
**[⬆ Back to Top](#table-of-contents)**
88. ### Are custom DOM attributes supported in React v16?
Yes. In the past, React used to ignore unknown DOM attributes. If you wrote JSX with an attribute that React doesn't recognize, React would just skip it.
For example, let's take a look at the below attribute:
```jsx harmony
<div mycustomattribute={"something"} />
```
Would render an empty div to the DOM with React v15:
```html
<div />
```
In React v16 any unknown attributes will end up in the DOM:
```html
<div mycustomattribute="something" />
```
This is useful for supplying browser-specific non-standard attributes, trying new DOM APIs, and integrating with opinionated third-party libraries.
**[⬆ Back to Top](#table-of-contents)**
89. ### What is the difference between constructor and getInitialState?
You should initialize state in the constructor when using ES6 classes, and `getInitialState()` method when using `React.createClass()`.
**Using ES6 classes:**
```javascript
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
/* initial state */
};
}
}
```
**Using `React.createClass()`:**
```javascript
const MyComponent = React.createClass({
getInitialState() {
return {
/* initial state */
};
},
});
```
**Note:** `React.createClass()` is deprecated and removed in React v16. Use plain JavaScript classes instead.
**[⬆ Back to Top](#table-of-contents)**
90. ### Can you force a component to re-render without calling setState?
By default, when your component's state or props change, your component will re-render. If your `render()` method depends on some other data, you can tell React that the component needs re-rendering by calling `forceUpdate()`.
```javascript
component.forceUpdate(callback);
```
It is recommended to avoid all uses of `forceUpdate()` and only read from `this.props` and `this.state` in `render()`.
**[⬆ Back to Top](#table-of-contents)**
91. ### What is the difference between `super()` and `super(props)` in React using ES6 classes?
When you want to access `this.props` in `constructor()` then you should pass props to `super()` method.
**Using `super(props)`:**
```javascript
class MyComponent extends React.Component {
constructor(props) {
super(props);
console.log(this.props); // { name: 'John', ... }
}
}
```
**Using `super()`:**
```javascript
class MyComponent extends React.Component {
constructor(props) {
super();
console.log(this.props); // undefined
}
}
```
Outside `constructor()` both will display same value for `this.props`.
**[⬆ Back to Top](#table-of-contents)**
92. ### How to loop inside JSX?
You can simply use `Array.prototype.map` with ES6 _arrow function_ syntax.
For example, the `items` array of objects is mapped into an array of components:
```jsx harmony
<tbody>
{items.map((item) => (
<SomeComponent key={item.id} name={item.name} />
))}
</tbody>
```
But you can't iterate using `for` loop:
```jsx harmony
<tbody>
for (let i = 0; i < items.length; i++) {
<SomeComponent key={items[i].id} name={items[i].name} />
}
</tbody>
```
This is because JSX tags are transpiled into _function calls_, and you can't use statements inside expressions. This may change thanks to `do` expressions which are _stage 1 proposal_.
**[⬆ Back to Top](#table-of-contents)**
93. ### How do you access props in attribute quotes?
React (or JSX) doesn't support variable interpolation inside an attribute value. The below representation won't work:
```jsx harmony
<img className="image" src="images/{this.props.image}" />
```
But you can put any JS expression inside curly braces as the entire attribute value. So the below expression works:
```jsx harmony
<img className="image" src={"images/" + this.props.image} />
```
Using _template strings_ will also work:
```jsx harmony
<img className="image" src={`images/${this.props.image}`} />
```
**[⬆ Back to Top](#table-of-contents)**
94. ### What is React proptype array with shape?
If you want to pass an array of objects to a component with a particular shape then use `React.PropTypes.shape()` as an argument to `React.PropTypes.arrayOf()`.
```javascript
ReactComponent.propTypes = {
arrayWithShape: React.PropTypes.arrayOf(
React.PropTypes.shape({
color: React.PropTypes.string.isRequired,
fontSize: React.PropTypes.number.isRequired,
})
).isRequired,
};
```
**[⬆ Back to Top](#table-of-contents)**
95. ### How to conditionally apply class attributes?
You shouldn't use curly braces inside quotes because it is going to be evaluated as a string.
```jsx harmony
<div className="btn-panel {this.props.visible ? 'show' : 'hidden'}">
```
Instead you need to move curly braces outside (don't forget to include spaces between class names):
```jsx harmony
<div className={'btn-panel ' + (this.props.visible ? 'show' : 'hidden')}>
```
_Template strings_ will also work:
```jsx harmony
<div className={`btn-panel ${this.props.visible ? 'show' : 'hidden'}`}>
```
**[⬆ Back to Top](#table-of-contents)**
96. ### What is the difference between React and ReactDOM?
The `react` package contains `React.createElement()`, `React.Component`, `React.Children`, and other helpers related to elements and component classes. You can think of these as the isomorphic or universal helpers that you need to build components. The `react-dom` package contains `ReactDOM.render()`, and in `react-dom/server` we have _server-side rendering_ support with `ReactDOMServer.renderToString()` and `ReactDOMServer.renderToStaticMarkup()`.
**[⬆ Back to Top](#table-of-contents)**
97. ### Why ReactDOM is separated from React?
The React team worked on extracting all DOM-related features into a separate library called _ReactDOM_. React v0.14 is the first release in which the libraries are split. By looking at some of the packages, `react-native`, `react-art`, `react-canvas`, and `react-three`, it has become clear that the beauty and essence of React has nothing to do with browsers or the DOM.
To build more environments that React can render to, React team planned to split the main React package into two: `react` and `react-dom`. This paves the way to writing components that can be shared between the web version of React and React Native.
**[⬆ Back to Top](#table-of-contents)**
98. ### How to use React label element?
If you try to render a `<label>` element bound to a text input using the standard `for` attribute, then it produces HTML missing that attribute and prints a warning to the console.
```jsx harmony
<label for={'user'}>{'User'}</label>
<input type={'text'} id={'user'} />
```
Since `for` is a reserved keyword in JavaScript, use `htmlFor` instead.
```jsx harmony
<label htmlFor={'user'}>{'User'}</label>
<input type={'text'} id={'user'} />
```
**[⬆ Back to Top](#table-of-contents)**
99. ### How to combine multiple inline style objects?
You can use _spread operator_ in regular React:
```jsx harmony
<button style={{ ...styles.panel.button, ...styles.panel.submitButton }}>
{"Submit"}
</button>
```
If you're using React Native then you can use the array notation:
```jsx harmony
<button style={[styles.panel.button, styles.panel.submitButton]}>
{"Submit"}
</button>
```
**[⬆ Back to Top](#table-of-contents)**
100. ### How to re-render the view when the browser is resized?
You can use the `useState` hook to manage the width and height state variables, and the `useEffect` hook to add and remove the `resize` event listener. The `[]` dependency array passed to useEffect ensures that the effect only runs once (on mount) and not on every re-render.
```javascript
import React, { useState, useEffect } from "react";
function WindowDimensions() {
const [dimensions, setDimensions] = useState({
width: window.innerWidth,
height: window.innerHeight,
});
useEffect(() => {
function handleResize() {
setDimensions({
width: window.innerWidth,
height: window.innerHeight,
});
}
window.addEventListener("resize", handleResize);
return () => window.removeEventListener("resize", handleResize);
}, []);
return (
<span>
{dimensions.width} x {dimensions.height}
</span>
);
}
```
<details>
<summary><h4>Using Class Component</h4></summary>
You can listen to the `resize` event in `componentDidMount()` and then update the dimensions (`width` and `height`). You should remove the listener in `componentWillUnmount()` method.
```javascript
class WindowDimensions extends React.Component {
constructor(props) {
super(props);
this.updateDimensions = this.updateDimensions.bind(this);
}
componentWillMount() {
this.updateDimensions();
}
componentDidMount() {
window.addEventListener("resize", this.updateDimensions);
}
componentWillUnmount() {
window.removeEventListener("resize", this.updateDimensions);
}
updateDimensions() {
this.setState({
width: window.innerWidth,
height: window.innerHeight,
});
}
render() {
return (
<span>
{this.state.width} x {this.state.height}
</span>
);
}
}
```
</details>
**[⬆ Back to Top](#table-of-contents)**
101. ### What is the difference between `setState()` and `replaceState()` methods?
When you use `setState()` the current and previous states are merged. `replaceState()` throws out the current state, and replaces it with only what you provide. Usually `setState()` is used unless you really need to remove all previous keys for some reason. You can also set state to `false`/`null` in `setState()` instead of using `replaceState()`.
**[⬆ Back to Top](#table-of-contents)**
102. ### How to listen to state changes?
The `componentDidUpdate` lifecycle method will be called when state changes. You can compare provided state and props values with current state and props to determine if something meaningful changed.
```
componentDidUpdate(object prevProps, object prevState)
```
**Note:** The previous releases of ReactJS also uses `componentWillUpdate(object nextProps, object nextState)` for state changes. It has been deprecated in latest releases.
**[⬆ Back to Top](#table-of-contents)**
103. ### What is the recommended approach of removing an array element in React state?
The better approach is to use `Array.prototype.filter()` method.
For example, let's create a `removeItem()` method for updating the state.
```javascript
removeItem(index) {
this.setState({
data: this.state.data.filter((item, i) => i !== index)
})
}
```
**[⬆ Back to Top](#table-of-contents)**
104. ### Is it possible to use React without rendering HTML?
It is possible. Below are the possible options:
```jsx harmony
render() {
return false
}
```
```jsx harmony
render() {
return true
}
```
```jsx harmony
render() {
return null
}
```
React version >=16.0.0:
```jsx harmony
render() {
return []
}
```
```jsx harmony
render() {
return ""
}
```
React version >=16.2.0:
```jsx harmony
render() {
return <React.Fragment></React.Fragment>
}
```
```jsx harmony
render() {
return <></>
}
```
React version >=18.0.0:
```jsx harmony
render() {
return undefined
}
```
**[⬆ Back to Top](#table-of-contents)**
105. ### How to pretty print JSON with React?
We can use `<pre>` tag so that the formatting of the `JSON.stringify()` is retained:
```jsx harmony
const data = { name: "John", age: 42 };
class User extends React.Component {
render() {
return <pre>{JSON.stringify(data, null, 2)}</pre>;
}
}
React.render(<User />, document.getElementById("container"));
```
**[⬆ Back to Top](#table-of-contents)**
106. ### Why you can't update props in React?
The React philosophy is that props should be _immutable_ and _top-down_. This means that a parent can send any prop values to a child, but the child can't modify received props.
**[⬆ Back to Top](#table-of-contents)**
107. ### How to focus an input element on page load?
You can do it by creating _ref_ for `input` element and using it in `componentDidMount()`:
```jsx harmony
class App extends React.Component {
componentDidMount() {
this.nameInput.focus();
}
render() {
return (
<div>
<input defaultValue={"Won't focus"} />
<input
ref={(input) => (this.nameInput = input)}
defaultValue={"Will focus"}
/>
</div>
);
}
}
ReactDOM.render(<App />, document.getElementById("app"));
```
Also in Functional component (react 16.08 and above)
```jsx harmony
import React, { useEffect, useRef } from "react";
const App = () => {
const inputElRef = useRef(null);
useEffect(() => {
inputElRef.current.focus();
}, []);
return (
<div>
<input defaultValue={"Won't focus"} />
<input ref={inputElRef} defaultValue={"Will focus"} />
</div>
);
};
ReactDOM.render(<App />, document.getElementById("app"));
```
**[⬆ Back to Top](#table-of-contents)**
108. ### What are the possible ways of updating objects in state?
1. **Calling `setState()` with an object to merge with state:**
- Using `Object.assign()` to create a copy of the object:
```javascript
const user = Object.assign({}, this.state.user, { age: 42 });
this.setState({ user });
```
- Using _spread operator_:
```javascript
const user = { ...this.state.user, age: 42 };
this.setState({ user });
```
2. **Calling `setState()` with a function:**
```javascript
this.setState((prevState) => ({
user: {
...prevState.user,
age: 42,
},
}));
```
**[⬆ Back to Top](#table-of-contents)**
110. ### How can we find the version of React at runtime in the browser?
You can use `React.version` to get the version.
```jsx harmony
const REACT_VERSION = React.version;
ReactDOM.render(
<div>{`React version: ${REACT_VERSION}`}</div>,
document.getElementById("app")
);
```
**[⬆ Back to Top](#table-of-contents)**
111. ### What are the approaches to include polyfills in your `create-react-app`?
There are approaches to include polyfills in create-react-app,
1. **Manual import from `core-js`:**
Create a file called (something like) `polyfills.js` and import it into root `index.js` file. Run `npm install core-js` or `yarn add core-js` and import your specific required features.
```javascript
import "core-js/fn/array/find";
import "core-js/fn/array/includes";
import "core-js/fn/number/is-nan";
```
2. **Using Polyfill service:**
Use the polyfill.io CDN to retrieve custom, browser-specific polyfills by adding this line to `index.html`:
```html
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=default,Array.prototype.includes"></script>
```
In the above script we had to explicitly request the `Array.prototype.includes` feature as it is not included in the default feature set.
**[⬆ Back to Top](#table-of-contents)**
112. ### How to use https instead of http in create-react-app?
You just need to use `HTTPS=true` configuration. You can edit your `package.json` scripts section:
```json
"scripts": {
"start": "set HTTPS=true && react-scripts start"
}
```
or just run `set HTTPS=true && npm start`
**[⬆ Back to Top](#table-of-contents)**
113. ### How to avoid using relative path imports in create-react-app?
Create a file called `.env` in the project root and write the import path:
```
NODE_PATH=src/app
```
After that restart the development server. Now you should be able to import anything inside `src/app` without relative paths.
**[⬆ Back to Top](#table-of-contents)**
114. ### How to add Google Analytics for React Router?
Add a listener on the `history` object to record each page view:
```javascript
history.listen(function (location) {
window.ga("set", "page", location.pathname + location.search);
window.ga("send", "pageview", location.pathname + location.search);
});
```
**[⬆ Back to Top](#table-of-contents)**
115. ### How to update a component every second?
You need to use `setInterval()` to trigger the change, but you also need to clear the timer when the component unmounts to prevent errors and memory leaks.
```javascript
componentDidMount() {
this.interval = setInterval(() => this.setState({ time: Date.now() }), 1000)
}
componentWillUnmount() {
clearInterval(this.interval)
}
```
**[⬆ Back to Top](#table-of-contents)**
116. ### How do you apply vendor prefixes to inline styles in React?
React _does not_ apply _vendor prefixes_ automatically. You need to add vendor prefixes manually.
```jsx harmony
<div
style={{
transform: "rotate(90deg)",
WebkitTransform: "rotate(90deg)", // note the capital 'W' here
msTransform: "rotate(90deg)", // 'ms' is the only lowercase vendor prefix
}}
/>
```
**[⬆ Back to Top](#table-of-contents)**
117. ### How to import and export components using React and ES6?
You should use default for exporting the components
```jsx harmony
import React from "react";
import User from "user";
export default class MyProfile extends React.Component {
render() {
return <User type="customer">//...</User>;
}
}
```
With the export specifier, the MyProfile is going to be the member and exported to this module and the same can be imported without mentioning the name in other components.
**[⬆ Back to Top](#table-of-contents)**
119. ### Why is a component constructor called only once?
React's _reconciliation_ algorithm assumes that without any information to the contrary, if a custom component appears in the same place on subsequent renders, it's the same component as before, so reuses the previous instance rather than creating a new one.
**[⬆ Back to Top](#table-of-contents)**
120. ### How to define constants in React?
You can use ES7 `static` field to define constant.
```javascript
class MyComponent extends React.Component {
static DEFAULT_PAGINATION = 10;
}
```
**[⬆ Back to Top](#table-of-contents)**
121. ### How to programmatically trigger click event in React?
You could use the ref prop to acquire a reference to the underlying `HTMLInputElement` object through a callback, store the reference as a class property, then use that reference to later trigger a click from your event handlers using the `HTMLElement.click` method.
This can be done in two steps:
1. Create ref in render method:
```jsx harmony
<input ref={(input) => (this.inputElement = input)} />
```
2. Apply click event in your event handler:
```javascript
this.inputElement.click();
```
**[⬆ Back to Top](#table-of-contents)**
122. ### Is it possible to use async/await in plain React?
If you want to use `async`/`await` in React, you will need _Babel_ and [transform-async-to-generator](https://babeljs.io/docs/en/babel-plugin-transform-async-to-generator) plugin. React Native ships with Babel and a set of transforms.
**[⬆ Back to Top](#table-of-contents)**
123. ### What are the common folder structures for React?
There are two common practices for React project file structure.
1. **Grouping by features or routes:**
One common way to structure projects is locate CSS, JS, and tests together, grouped by feature or route.
```
common/
├─ Avatar.js
├─ Avatar.css
├─ APIUtils.js
└─ APIUtils.test.js
feed/
├─ index.js
├─ Feed.js
├─ Feed.css
├─ FeedStory.js
├─ FeedStory.test.js
└─ FeedAPI.js
profile/
├─ index.js
├─ Profile.js
├─ ProfileHeader.js
├─ ProfileHeader.css
└─ ProfileAPI.js
```
2. **Grouping by file type:**
Another popular way to structure projects is to group similar files together.
```
api/
├─ APIUtils.js
├─ APIUtils.test.js
├─ ProfileAPI.js
└─ UserAPI.js
components/
├─ Avatar.js
├─ Avatar.css
├─ Feed.js
├─ Feed.css
├─ FeedStory.js
├─ FeedStory.test.js
├─ Profile.js
├─ ProfileHeader.js
└─ ProfileHeader.css
```
**[⬆ Back to Top](#table-of-contents)**
124. ### What are the popular packages for animation?
_React Transition Group_ and _React Motion_ are popular animation packages in React ecosystem.
**[⬆ Back to Top](#table-of-contents)**
125. ### What is the benefit of styles modules?
It is recommended to avoid hard coding style values in components. Any values that are likely to be used across different UI components should be extracted into their own modules.
For example, these styles could be extracted into a separate component:
```javascript
export const colors = {
white,
black,
blue,
};
export const space = [0, 8, 16, 32, 64];
```
And then imported individually in other components:
```javascript
import { space, colors } from "./styles";
```
**[⬆ Back to Top](#table-of-contents)**
126. ### What are the popular React-specific linters?
ESLint is a popular JavaScript linter. There are plugins available that analyse specific code styles. One of the most common for React is an npm package called `eslint-plugin-react`. By default, it will check a number of best practices, with rules checking things from keys in iterators to a complete set of prop types.
Another popular plugin is `eslint-plugin-jsx-a11y`, which will help fix common issues with accessibility. As JSX offers slightly different syntax to regular HTML, issues with `alt` text and `tabindex`, for example, will not be picked up by regular plugins.
**[⬆ Back to Top](#table-of-contents)**
127. ### How to make AJAX call and in which component lifecycle methods should I make an AJAX call?
You can use AJAX libraries such as Axios, jQuery AJAX, and the browser built-in `fetch`. You should fetch data in the `componentDidMount()` lifecycle method. This is so you can use `setState()` to update your component when the data is retrieved.
For example, the employees list fetched from API and set local state:
```jsx harmony
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
employees: [],
error: null,
};
}
componentDidMount() {
fetch("https://api.example.com/items")
.then((res) => res.json())
.then(
(result) => {
this.setState({
employees: result.employees,
});
},
(error) => {
this.setState({ error });
}
);
}
render() {
const { error, employees } = this.state;
if (error) {
return <div>Error: {error.message}</div>;
} else {
return (
<ul>
{employees.map((employee) => (
<li key={employee.name}>
{employee.name}-{employee.experience}
</li>
))}
</ul>
);
}
}
}
```
**[⬆ Back to Top](#table-of-contents)**
128. ### What are render props?
**Render Props** is a simple technique for sharing code between components using a prop whose value is a function. The below component uses render prop which returns a React element.
```jsx harmony
<DataProvider render={(data) => <h1>{`Hello ${data.target}`}</h1>} />
```
Libraries such as React Router and DownShift are using this pattern.
## React Router
**[⬆ Back to Top](#table-of-contents)**
129. ### What is React Router?
React Router is a powerful routing library built on top of React that helps you add new screens and flows to your application incredibly quickly, all while keeping the URL in sync with what's being displayed on the page.
**[⬆ Back to Top](#table-of-contents)**
130. ### How React Router is different from history library?
React Router is a wrapper around the `history` library which handles interaction with the browser's `window.history` with its browser and hash histories. It also provides memory history which is useful for environments that don't have global history, such as mobile app development (React Native) and unit testing with Node.
**[⬆ Back to Top](#table-of-contents)**
131. ### What are the `<Router>` components of React Router v4?
React Router v4 provides below 3 `<Router>` components:
1. `<BrowserRouter>`
2. `<HashRouter>`
3. `<MemoryRouter>`
The above components will create _browser_, _hash_, and _memory_ history instances. React Router v4 makes the properties and methods of the `history` instance associated with your router available through the context in the `router` object.
**[⬆ Back to Top](#table-of-contents)**
132. ### What is the purpose of `push()` and `replace()` methods of `history`?
A history instance has two methods for navigation purpose.
1. `push()`
2. `replace()`
If you think of the history as an array of visited locations, `push()` will add a new location to the array and `replace()` will replace the current location in the array with the new one.
**[⬆ Back to Top](#table-of-contents)**
133. ### How do you programmatically navigate using React Router v4?
There are three different ways to achieve programmatic routing/navigation within components.
1. **Using the `withRouter()` higher-order function:**
The `withRouter()` higher-order function will inject the history object as a prop of the component. This object provides `push()` and `replace()` methods to avoid the usage of context.
```jsx harmony
import { withRouter } from "react-router-dom"; // this also works with 'react-router-native'
const Button = withRouter(({ history }) => (
<button
type="button"
onClick={() => {
history.push("/new-location");
}}
>
{"Click Me!"}
</button>
));
```
2. **Using `<Route>` component and render props pattern:**
The `<Route>` component passes the same props as `withRouter()`, so you will be able to access the history methods through the history prop.
```jsx harmony
import { Route } from "react-router-dom";
const Button = () => (
<Route
render={({ history }) => (
<button
type="button"
onClick={() => {
history.push("/new-location");
}}
>
{"Click Me!"}
</button>
)}
/>
);
```
3. **Using context:**
This option is not recommended and treated as unstable API.
```jsx harmony
const Button = (props, context) => (
<button
type="button"
onClick={() => {
context.history.push("/new-location");
}}
>
{"Click Me!"}
</button>
);
Button.contextTypes = {
history: React.PropTypes.shape({
push: React.PropTypes.func.isRequired,
}),
};
```
**[⬆ Back to Top](#table-of-contents)**
134. ### How to get query parameters in React Router v4?
The ability to parse query strings was taken out of React Router v4 because there have been user requests over the years to support different implementation. So the decision has been given to users to choose the implementation they like. The recommended approach is to use query strings library.
```javascript
const queryString = require("query-string");
const parsed = queryString.parse(props.location.search);
```
You can also use `URLSearchParams` if you want something native:
```javascript
const params = new URLSearchParams(props.location.search);
const foo = params.get("name");
```
You should use a _polyfill_ for IE11.
**[⬆ Back to Top](#table-of-contents)**
135. ### Why you get "Router may have only one child element" warning?
You have to wrap your Route's in a `<Switch>` block because `<Switch>` is unique in that it renders a route exclusively.
At first you need to add `Switch` to your imports:
```javascript
import { Switch, Router, Route } from "react-router";
```
Then define the routes within `<Switch>` block:
```jsx harmony
<Router>
<Switch>
<Route {/* ... */} />
<Route {/* ... */} />
</Switch>
</Router>
```
**[⬆ Back to Top](#table-of-contents)**
136. ### How to pass params to `history.push` method in React Router v4?
While navigating you can pass props to the `history` object:
```javascript
this.props.history.push({
pathname: "/template",
search: "?name=sudheer",
state: { detail: response.data },
});
```
The `search` property is used to pass query params in `push()` method.
**[⬆ Back to Top](#table-of-contents)**
137. ### How to implement _default_ or _NotFound_ page?
A `<Switch>` renders the first child `<Route>` that matches. A `<Route>` with no path always matches. So you just need to simply drop path attribute as below
```jsx harmony
<Switch>
<Route exact path="/" component={Home} />
<Route path="/user" component={User} />
<Route component={NotFound} />
</Switch>
```
**[⬆ Back to Top](#table-of-contents)**
138. ### How to get history on React Router v4?
Below are the list of steps to get history object on React Router v4,
1. Create a module that exports a `history` object and import this module across the project.
For example, create `history.js` file:
```javascript
import { createBrowserHistory } from "history";
export default createBrowserHistory({
/* pass a configuration object here if needed */
});
```
2. You should use the `<Router>` component instead of built-in routers. Import the above `history.js` inside `index.js` file:
```jsx harmony
import { Router } from "react-router-dom";
import history from "./history";
import App from "./App";
ReactDOM.render(
<Router history={history}>
<App />
</Router>,
holder
);
```
3. You can also use push method of `history` object similar to built-in history object:
```javascript
// some-other-file.js
import history from "./history";
history.push("/go-here");
```
**[⬆ Back to Top](#table-of-contents)**
139. ### How to perform automatic redirect after login?
The `react-router` package provides `<Redirect>` component in React Router. Rendering a `<Redirect>` will navigate to a new location. Like server-side redirects, the new location will override the current location in the history stack.
```javascript
import React, { Component } from "react";
import { Redirect } from "react-router";
export default class LoginComponent extends Component {
render() {
if (this.state.isLoggedIn === true) {
return <Redirect to="/your/redirect/page" />;
} else {
return <div>{"Login Please"}</div>;
}
}
}
```
## React Internationalization
**[⬆ Back to Top](#table-of-contents)**
140. ### What is React Intl?
The _React Intl_ library makes internationalization in React straightforward, with off-the-shelf components and an API that can handle everything from formatting strings, dates, and numbers, to pluralization. React Intl is part of _FormatJS_ which provides bindings to React via its components and API.
**[⬆ Back to Top](#table-of-contents)**
141. ### What are the main features of React Intl?
Below are the main features of React Intl,
1. Display numbers with separators.
2. Display dates and times correctly.
3. Display dates relative to "now".
4. Pluralize labels in strings.
5. Support for 150+ languages.
6. Runs in the browser and Node.
7. Built on standards.
**[⬆ Back to Top](#table-of-contents)**
142. ### What are the two ways of formatting in React Intl?
The library provides two ways to format strings, numbers, and dates:
1. **Using react components:**
```jsx harmony
<FormattedMessage
id={"account"}
defaultMessage={"The amount is less than minimum balance."}
/>
```
2. **Using an API:**
```javascript
const messages = defineMessages({
accountMessage: {
id: "account",
defaultMessage: "The amount is less than minimum balance.",
},
});
formatMessage(messages.accountMessage);
```
**[⬆ Back to Top](#table-of-contents)**
143. ### How to use `<FormattedMessage>` as placeholder using React Intl?
The `<Formatted... />` components from `react-intl` return elements, not plain text, so they can't be used for placeholders, alt text, etc. In that case, you should use lower level API `formatMessage()`. You can inject the `intl` object into your component using `injectIntl()` higher-order component and then format the message using `formatMessage()` available on that object.
```jsx harmony
import React from "react";
import { injectIntl, intlShape } from "react-intl";
const MyComponent = ({ intl }) => {
const placeholder = intl.formatMessage({ id: "messageId" });
return <input placeholder={placeholder} />;
};
MyComponent.propTypes = {
intl: intlShape.isRequired,
};
export default injectIntl(MyComponent);
```
**[⬆ Back to Top](#table-of-contents)**
144. ### How to access current locale with React Intl?
You can get the current locale in any component of your application using `injectIntl()`:
```jsx harmony
import { injectIntl, intlShape } from "react-intl";
const MyComponent = ({ intl }) => (
<div>{`The current locale is ${intl.locale}`}</div>
);
MyComponent.propTypes = {
intl: intlShape.isRequired,
};
export default injectIntl(MyComponent);
```
**[⬆ Back to Top](#table-of-contents)**
145. ### How to format date using React Intl?
The `injectIntl()` higher-order component will give you access to the `formatDate()` method via the props in your component. The method is used internally by instances of `FormattedDate` and it returns the string representation of the formatted date.
```jsx harmony
import { injectIntl, intlShape } from "react-intl";
const stringDate = this.props.intl.formatDate(date, {
year: "numeric",
month: "numeric",
day: "numeric",
});
const MyComponent = ({ intl }) => (
<div>{`The formatted date is ${stringDate}`}</div>
);
MyComponent.propTypes = {
intl: intlShape.isRequired,
};
export default injectIntl(MyComponent);
```
## React Testing
**[⬆ Back to Top](#table-of-contents)**
146. ### What is Shallow Renderer in React testing?
_Shallow rendering_ is useful for writing unit test cases in React. It lets you render a component _one level deep_ and assert facts about what its render method returns, without worrying about the behavior of child components, which are not instantiated or rendered.
For example, if you have the following component:
```javascript
function MyComponent() {
return (
<div>
<span className={"heading"}>{"Title"}</span>
<span className={"description"}>{"Description"}</span>
</div>
);
}
```
Then you can assert as follows:
```jsx harmony
import ShallowRenderer from "react-test-renderer/shallow";
// in your test
const renderer = new ShallowRenderer();
renderer.render(<MyComponent />);
const result = renderer.getRenderOutput();
expect(result.type).toBe("div");
expect(result.props.children).toEqual([
<span className={"heading"}>{"Title"}</span>,
<span className={"description"}>{"Description"}</span>,
]);
```
**[⬆ Back to Top](#table-of-contents)**
147. ### What is `TestRenderer` package in React?
This package provides a renderer that can be used to render components to pure JavaScript objects, without depending on the DOM or a native mobile environment. This package makes it easy to grab a snapshot of the platform view hierarchy (similar to a DOM tree) rendered by a ReactDOM or React Native without using a browser or `jsdom`.
```jsx harmony
import TestRenderer from "react-test-renderer";
const Link = ({ page, children }) => <a href={page}>{children}</a>;
const testRenderer = TestRenderer.create(
<Link page={"https://www.facebook.com/"}>{"Facebook"}</Link>
);
console.log(testRenderer.toJSON());
// {
// type: 'a',
// props: { href: 'https://www.facebook.com/' },
// children: [ 'Facebook' ]
// }
```
**[⬆ Back to Top](#table-of-contents)**
148. ### What is the purpose of ReactTestUtils package?
_ReactTestUtils_ are provided in the `with-addons` package and allow you to perform actions against a simulated DOM for the purpose of unit testing.
**[⬆ Back to Top](#table-of-contents)**
149. ### What is Jest?
_Jest_ is a JavaScript unit testing framework created by Facebook based on Jasmine and provides automated mock creation and a `jsdom` environment. It's often used for testing components.
**[⬆ Back to Top](#table-of-contents)**
150. ### What are the advantages of Jest over Jasmine?
There are couple of advantages compared to Jasmine:
- Automatically finds tests to execute in your source code.
- Automatically mocks dependencies when running your tests.
- Allows you to test asynchronous code synchronously.
- Runs your tests with a fake DOM implementation (via `jsdom`) so that your tests can be run on the command line.
- Runs tests in parallel processes so that they finish sooner.
**[⬆ Back to Top](#table-of-contents)**
151. ### Give a simple example of Jest test case
Let's write a test for a function that adds two numbers in `sum.js` file:
```javascript
const sum = (a, b) => a + b;
export default sum;
```
Create a file named `sum.test.js` which contains actual test:
```javascript
import sum from "./sum";
test("adds 1 + 2 to equal 3", () => {
expect(sum(1, 2)).toBe(3);
});
```
And then add the following section to your `package.json`:
```json
{
"scripts": {
"test": "jest"
}
}
```
Finally, run `yarn test` or `npm test` and Jest will print a result:
```console
$ yarn test
PASS ./sum.test.js
✓ adds 1 + 2 to equal 3 (2ms)
```
## React Redux
**[⬆ Back to Top](#table-of-contents)**
152. ### What is flux?
_Flux_ is an _application design paradigm_ used as a replacement for the more traditional MVC pattern. It is not a framework or a library but a new kind of architecture that complements React and the concept of Unidirectional Data Flow. Facebook uses this pattern internally when working with React.
The workflow between dispatcher, stores and views components with distinct inputs and outputs as follows:
**[⬆ Back to Top](#table-of-contents)**
153. ### What is Redux?
_Redux_ is a predictable state container for JavaScript apps based on the _Flux design pattern_. Redux can be used together with React, or with any other view library. It is tiny (about 2kB) and has no dependencies.
**[⬆ Back to Top](#table-of-contents)**
154. ### What are the core principles of Redux?
Redux follows three fundamental principles:
1. **Single source of truth:** The state of your whole application is stored in an object tree within a single store. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.
2. **State is read-only:** The only way to change the state is to emit an action, an object describing what happened. This ensures that neither the views nor the network callbacks will ever write directly to the state.
3. **Changes are made with pure functions:** To specify how the state tree is transformed by actions, you write reducers. Reducers are just pure functions that take the previous state and an action as parameters, and return the next state.
**[⬆ Back to Top](#table-of-contents)**
155. ### What are the downsides of Redux compared to Flux?
Instead of saying downsides we can say that there are few compromises of using Redux over Flux. Those are as follows:
1. **You will need to learn to avoid mutations:** Flux is un-opinionated about mutating data, but Redux doesn't like mutations and many packages complementary to Redux assume you never mutate the state. You can enforce this with dev-only packages like `redux-immutable-state-invariant`, Immutable.js, or instructing your team to write non-mutating code.
2. **You're going to have to carefully pick your packages:** While Flux explicitly doesn't try to solve problems such as undo/redo, persistence, or forms, Redux has extension points such as middleware and store enhancers, and it has spawned a rich ecosystem.
3. **There is no nice Flow integration yet:** Flux currently lets you do very impressive static type checks which Redux doesn't support yet.
**[⬆ Back to Top](#table-of-contents)**
156. ### What is the difference between `mapStateToProps()` and `mapDispatchToProps()`?
`mapStateToProps()` is a utility which helps your component get updated state (which is updated by some other components):
```javascript
const mapStateToProps = (state) => {
return {
todos: getVisibleTodos(state.todos, state.visibilityFilter),
};
};
```
`mapDispatchToProps()` is a utility which will help your component to fire an action event (dispatching action which may cause change of application state):
```javascript
const mapDispatchToProps = (dispatch) => {
return {
onTodoClick: (id) => {
dispatch(toggleTodo(id));
},
};
};
```
It is recommended to always use the “object shorthand” form for the `mapDispatchToProps`.
Redux wraps it in another function that looks like (…args) => dispatch(onTodoClick(…args)), and pass that wrapper function as a prop to your component.
```javascript
const mapDispatchToProps = {
onTodoClick,
};
```
**[⬆ Back to Top](#table-of-contents)**
157. ### Can I dispatch an action in reducer?
Dispatching an action within a reducer is an **anti-pattern**. Your reducer should be _without side effects_, simply digesting the action payload and returning a new state object. Adding listeners and dispatching actions within the reducer can lead to chained actions and other side effects.
**[⬆ Back to Top](#table-of-contents)**
158. ### How to access Redux store outside a component?
You just need to export the store from the module where it created with `createStore()`. Also, it shouldn't pollute the global window object.
```javascript
store = createStore(myReducer);
export default store;
```
**[⬆ Back to Top](#table-of-contents)**
159. ### What are the drawbacks of MVW pattern?
1. DOM manipulation is very expensive which causes applications to behave slow and inefficient.
2. Due to circular dependencies, a complicated model was created around models and views.
3. Lot of data changes happens for collaborative applications(like Google Docs).
4. No way to do undo (travel back in time) easily without adding so much extra code.
**[⬆ Back to Top](#table-of-contents)**
160. ### Are there any similarities between Redux and RxJS?
These libraries are very different for very different purposes, but there are some vague similarities.
Redux is a tool for managing state throughout the application. It is usually used as an architecture for UIs. Think of it as an alternative to (half of) Angular. RxJS is a reactive programming library. It is usually used as a tool to accomplish asynchronous tasks in JavaScript. Think of it as an alternative to Promises. Redux uses the Reactive paradigm because the Store is reactive. The Store observes actions from a distance, and changes itself. RxJS also uses the Reactive paradigm, but instead of being an architecture, it gives you basic building blocks, Observables, to accomplish this pattern.
**[⬆ Back to Top](#table-of-contents)**
161. ### How to dispatch an action on load?
You can dispatch an action in `componentDidMount()` method and in `render()` method you can verify the data.
```javascript
class App extends Component {
componentDidMount() {
this.props.fetchData();
}
render() {
return this.props.isLoaded ? (
<div>{"Loaded"}</div>
) : (
<div>{"Not Loaded"}</div>
);
}
}
const mapStateToProps = (state) => ({
isLoaded: state.isLoaded,
});
const mapDispatchToProps = { fetchData };
export default connect(mapStateToProps, mapDispatchToProps)(App);
```
**[⬆ Back to Top](#table-of-contents)**
162. ### How to use `connect()` from React Redux?
You need to follow two steps to use your store in your container:
1. **Use `mapStateToProps()`:** It maps the state variables from your store to the props that you specify.
2. **Connect the above props to your container:** The object returned by the `mapStateToProps` function is connected to the container. You can import `connect()` from `react-redux`.
```jsx harmony
import React from "react";
import { connect } from "react-redux";
class App extends React.Component {
render() {
return <div>{this.props.containerData}</div>;
}
}
function mapStateToProps(state) {
return { containerData: state.data };
}
export default connect(mapStateToProps)(App);
```
**[⬆ Back to Top](#table-of-contents)**
163. ### How to reset state in Redux?
You need to write a _root reducer_ in your application which delegate handling the action to the reducer generated by `combineReducers()`.
For example, let us take `rootReducer()` to return the initial state after `USER_LOGOUT` action. As we know, reducers are supposed to return the initial state when they are called with `undefined` as the first argument, no matter the action.
```javascript
const appReducer = combineReducers({
/* your app's top-level reducers */
});
const rootReducer = (state, action) => {
if (action.type === "USER_LOGOUT") {
state = undefined;
}
return appReducer(state, action);
};
```
In case of using `redux-persist`, you may also need to clean your storage. `redux-persist` keeps a copy of your state in a storage engine. First, you need to import the appropriate storage engine and then, to parse the state before setting it to undefined and clean each storage state key.
```javascript
const appReducer = combineReducers({
/* your app's top-level reducers */
});
const rootReducer = (state, action) => {
if (action.type === "USER_LOGOUT") {
Object.keys(state).forEach((key) => {
storage.removeItem(`persist:${key}`);
});
state = undefined;
}
return appReducer(state, action);
};
```
**[⬆ Back to Top](#table-of-contents)**
164. ### Whats the purpose of `at` symbol in the Redux connect decorator?
The **@** symbol is in fact a JavaScript expression used to signify decorators. _Decorators_ make it possible to annotate and modify classes and properties at design time.
Let's take an example setting up Redux without and with a decorator.
- **Without decorator:**
```javascript
import React from "react";
import * as actionCreators from "./actionCreators";
import { bindActionCreators } from "redux";
import { connect } from "react-redux";
function mapStateToProps(state) {
return { todos: state.todos };
}
function mapDispatchToProps(dispatch) {
return { actions: bindActionCreators(actionCreators, dispatch) };
}
class MyApp extends React.Component {
// ...define your main app here
}
export default connect(mapStateToProps, mapDispatchToProps)(MyApp);
```
- **With decorator:**
```javascript
import React from "react";
import * as actionCreators from "./actionCreators";
import { bindActionCreators } from "redux";
import { connect } from "react-redux";
function mapStateToProps(state) {
return { todos: state.todos };
}
function mapDispatchToProps(dispatch) {
return { actions: bindActionCreators(actionCreators, dispatch) };
}
@connect(mapStateToProps, mapDispatchToProps)
export default class MyApp extends React.Component {
// ...define your main app here
}
```
The above examples are almost similar except the usage of decorator. The decorator syntax isn't built into any JavaScript runtimes yet, and is still experimental and subject to change. You can use babel for the decorators support.
**[⬆ Back to Top](#table-of-contents)**
165. ### What is the difference between React context and React Redux?
You can use **Context** in your application directly and is going to be great for passing down data to deeply nested components which what it was designed for.
Whereas **Redux** is much more powerful and provides a large number of features that the Context API doesn't provide. Also, React Redux uses context internally but it doesn't expose this fact in the public API.
**[⬆ Back to Top](#table-of-contents)**
166. ### Why are Redux state functions called reducers?
Reducers always return the accumulation of the state (based on all previous and current actions). Therefore, they act as a reducer of state. Each time a Redux reducer is called, the state and action are passed as parameters. This state is then reduced (or accumulated) based on the action, and then the next state is returned. You could _reduce_ a collection of actions and an initial state (of the store) on which to perform these actions to get the resulting final state.
**[⬆ Back to Top](#table-of-contents)**
167. ### How to make AJAX request in Redux?
You can use `redux-thunk` middleware which allows you to define async actions.
Let's take an example of fetching specific account as an AJAX call using _fetch API_:
```javascript
export function fetchAccount(id) {
return (dispatch) => {
dispatch(setLoadingAccountState()); // Show a loading spinner
fetch(`/account/${id}`, (response) => {
dispatch(doneFetchingAccount()); // Hide loading spinner
if (response.status === 200) {
dispatch(setAccount(response.json)); // Use a normal function to set the received state
} else {
dispatch(someError);
}
});
};
}
function setAccount(data) {
return { type: "SET_Account", data: data };
}
```
**[⬆ Back to Top](#table-of-contents)**
168. ### Should I keep all component's state in Redux store?
Keep your data in the Redux store, and the UI related state internally in the component.
**[⬆ Back to Top](#table-of-contents)**
169. ### What is the proper way to access Redux store?
The best way to access your store in a component is to use the `connect()` function, that creates a new component that wraps around your existing one. This pattern is called _Higher-Order Components_, and is generally the preferred way of extending a component's functionality in React. This allows you to map state and action creators to your component, and have them passed in automatically as your store updates.
Let's take an example of `<FilterLink>` component using connect:
```javascript
import { connect } from "react-redux";
import { setVisibilityFilter } from "../actions";
import Link from "../components/Link";
const mapStateToProps = (state, ownProps) => ({
active: ownProps.filter === state.visibilityFilter,
});
const mapDispatchToProps = (dispatch, ownProps) => ({
onClick: () => dispatch(setVisibilityFilter(ownProps.filter)),
});
const FilterLink = connect(mapStateToProps, mapDispatchToProps)(Link);
export default FilterLink;
```
Due to it having quite a few performance optimizations and generally being less likely to cause bugs, the Redux developers almost always recommend using `connect()` over accessing the store directly (using context API).
```javascript
class MyComponent {
someMethod() {
doSomethingWith(this.context.store);
}
}
```
**[⬆ Back to Top](#table-of-contents)**
170. ### What is the difference between component and container in React Redux?
**Component** is a class or function component that describes the presentational part of your application.
**Container** is an informal term for a component that is connected to a Redux store. Containers _subscribe_ to Redux state updates and _dispatch_ actions, and they usually don't render DOM elements; they delegate rendering to presentational child components.
**[⬆ Back to Top](#table-of-contents)**
171. ### What is the purpose of the constants in Redux?
Constants allows you to easily find all usages of that specific functionality across the project when you use an IDE. It also prevents you from introducing silly bugs caused by typos – in which case, you will get a `ReferenceError` immediately.
Normally we will save them in a single file (`constants.js` or `actionTypes.js`).
```javascript
export const ADD_TODO = "ADD_TODO";
export const DELETE_TODO = "DELETE_TODO";
export const EDIT_TODO = "EDIT_TODO";
export const COMPLETE_TODO = "COMPLETE_TODO";
export const COMPLETE_ALL = "COMPLETE_ALL";
export const CLEAR_COMPLETED = "CLEAR_COMPLETED";
```
In Redux, you use them in two places:
1. **During action creation:**
Let's take `actions.js`:
```javascript
import { ADD_TODO } from "./actionTypes";
export function addTodo(text) {
return { type: ADD_TODO, text };
}
```
2. **In reducers:**
Let's create `reducer.js`:
```javascript
import { ADD_TODO } from "./actionTypes";
export default (state = [], action) => {
switch (action.type) {
case ADD_TODO:
return [
...state,
{
text: action.text,
completed: false,
},
];
default:
return state;
}
};
```
**[⬆ Back to Top](#table-of-contents)**
172. ### What are the different ways to write `mapDispatchToProps()`?
There are a few ways of binding _action creators_ to `dispatch()` in `mapDispatchToProps()`.
Below are the possible options:
```javascript
const mapDispatchToProps = (dispatch) => ({
action: () => dispatch(action()),
});
```
```javascript
const mapDispatchToProps = (dispatch) => ({
action: bindActionCreators(action, dispatch),
});
```
```javascript
const mapDispatchToProps = { action };
```
The third option is just a shorthand for the first one.
**[⬆ Back to Top](#table-of-contents)**
173. ### What is the use of the `ownProps` parameter in `mapStateToProps()` and `mapDispatchToProps()`?
If the `ownProps` parameter is specified, React Redux will pass the props that were passed to the component into your _connect_ functions. So, if you use a connected component:
```jsx harmony
import ConnectedComponent from "./containers/ConnectedComponent";
<ConnectedComponent user={"john"} />;
```
The `ownProps` inside your `mapStateToProps()` and `mapDispatchToProps()` functions will be an object:
```javascript
{
user: "john";
}
```
You can use this object to decide what to return from those functions.
**[⬆ Back to Top](#table-of-contents)**
174. ### How to structure Redux top level directories?
Most of the applications has several top-level directories as below:
1. **Components**: Used for _dumb_ components unaware of Redux.
2. **Containers**: Used for _smart_ components connected to Redux.
3. **Actions**: Used for all action creators, where file names correspond to part of the app.
4. **Reducers**: Used for all reducers, where files name correspond to state key.
5. **Store**: Used for store initialization.
This structure works well for small and medium size apps.
**[⬆ Back to Top](#table-of-contents)**
175. ### What is redux-saga?
`redux-saga` is a library that aims to make side effects (asynchronous things like data fetching and impure things like accessing the browser cache) in React/Redux applications easier and better.
It is available in NPM:
```console
$ npm install --save redux-saga
```
**[⬆ Back to Top](#table-of-contents)**
176. ### What is the mental model of redux-saga?
_Saga_ is like a separate thread in your application, that's solely responsible for side effects. `redux-saga` is a redux _middleware_, which means this thread can be started, paused and cancelled from the main application with normal Redux actions, it has access to the full Redux application state and it can dispatch Redux actions as well.
**[⬆ Back to Top](#table-of-contents)**
177. ### What are the differences between `call()` and `put()` in redux-saga?
Both `call()` and `put()` are effect creator functions. `call()` function is used to create effect description, which instructs middleware to call the promise. `put()` function creates an effect, which instructs middleware to dispatch an action to the store.
Let's take example of how these effects work for fetching particular user data.
```javascript
function* fetchUserSaga(action) {
// `call` function accepts rest arguments, which will be passed to `api.fetchUser` function.
// Instructing middleware to call promise, it resolved value will be assigned to `userData` variable
const userData = yield call(api.fetchUser, action.userId);
// Instructing middleware to dispatch corresponding action.
yield put({
type: "FETCH_USER_SUCCESS",
userData,
});
}
```
**[⬆ Back to Top](#table-of-contents)**
178. ### What is Redux Thunk?
_Redux Thunk_ middleware allows you to write action creators that return a function instead of an action. The thunk can be used to delay the dispatch of an action, or to dispatch only if a certain condition is met. The inner function receives the store methods `dispatch()` and `getState()` as parameters.
**[⬆ Back to Top](#table-of-contents)**
179. ### What are the differences between `redux-saga` and `redux-thunk`?
Both _Redux Thunk_ and _Redux Saga_ take care of dealing with side effects. In most of the scenarios, Thunk uses _Promises_ to deal with them, whereas Saga uses _Generators_. Thunk is simple to use and Promises are familiar to many developers, Sagas/Generators are more powerful but you will need to learn them. But both middleware can coexist, so you can start with Thunks and introduce Sagas when/if you need them.
**[⬆ Back to Top](#table-of-contents)**
180. ### What is Redux DevTools?
_Redux DevTools_ is a live-editing time travel environment for Redux with hot reloading, action replay, and customizable UI. If you don't want to bother with installing Redux DevTools and integrating it into your project, consider using Redux DevTools Extension for Chrome and Firefox.
**[⬆ Back to Top](#table-of-contents)**
181. ### What are the features of Redux DevTools?
Some of the main features of Redux DevTools are below,
1. Lets you inspect every state and action payload.
2. Lets you go back in time by _cancelling_ actions.
3. If you change the reducer code, each _staged_ action will be re-evaluated.
4. If the reducers throw, you will see during which action this happened, and what the error was.
5. With `persistState()` store enhancer, you can persist debug sessions across page reloads.
**[⬆ Back to Top](#table-of-contents)**
182. ### What are Redux selectors and why to use them?
_Selectors_ are functions that take Redux state as an argument and return some data to pass to the component.
For example, to get user details from the state:
```javascript
const getUserData = (state) => state.user.data;
```
These selectors have two main benefits,
1. The selector can compute derived data, allowing Redux to store the minimal possible state
2. The selector is not recomputed unless one of its arguments changes
**[⬆ Back to Top](#table-of-contents)**
183. ### What is Redux Form?
_Redux Form_ works with React and Redux to enable a form in React to use Redux to store all of its state. Redux Form can be used with raw HTML5 inputs, but it also works very well with common UI frameworks like Material UI, React Widgets and React Bootstrap.
**[⬆ Back to Top](#table-of-contents)**
184. ### What are the main features of Redux Form?
Some of the main features of Redux Form are:
1. Field values persistence via Redux store.
2. Validation (sync/async) and submission.
3. Formatting, parsing and normalization of field values.
**[⬆ Back to Top](#table-of-contents)**
185. ### How to add multiple middlewares to Redux?
You can use `applyMiddleware()`.
For example, you can add `redux-thunk` and `logger` passing them as arguments to `applyMiddleware()`:
```javascript
import { createStore, applyMiddleware } from "redux";
const createStoreWithMiddleware = applyMiddleware(
ReduxThunk,
logger
)(createStore);
```
**[⬆ Back to Top](#table-of-contents)**
186. ### How to set initial state in Redux?
You need to pass initial state as second argument to createStore:
```javascript
const rootReducer = combineReducers({
todos: todos,
visibilityFilter: visibilityFilter,
});
const initialState = {
todos: [{ id: 123, name: "example", completed: false }],
};
const store = createStore(rootReducer, initialState);
```
**[⬆ Back to Top](#table-of-contents)**
187. ### How Relay is different from Redux?
Relay is similar to Redux in that they both use a single store. The main difference is that relay only manages state originated from the server, and all access to the state is used via _GraphQL_ queries (for reading data) and mutations (for changing data). Relay caches the data for you and optimizes data fetching for you, by fetching only changed data and nothing more.
188. ### What is an action in Redux?
_Actions_ are plain JavaScript objects or payloads of information that send data from your application to your store. They are the only source of information for the store. Actions must have a type property that indicates the type of action being performed.
For example, let's take an action which represents adding a new todo item:
```
{
type: ADD_TODO,
text: 'Add todo item'
}
```
**[⬆ Back to Top](#table-of-contents)**
## React Native
**[⬆ Back to Top](#table-of-contents)**
188. ### What is the difference between React Native and React?
**React** is a JavaScript library, supporting both front end web and being run on the server, for building user interfaces and web applications.
**React Native** is a mobile framework that compiles to native app components, allowing you to build native mobile applications (iOS, Android, and Windows) in JavaScript that allows you to use React to build your components, and implements React under the hood.
**[⬆ Back to Top](#table-of-contents)**
189. ### How to test React Native apps?
React Native can be tested only in mobile simulators like iOS and Android. You can run the app in your mobile using expo app (https://expo.io) Where it syncs using QR code, your mobile and computer should be in same wireless network.
**[⬆ Back to Top](#table-of-contents)**
190. ### How to do logging in React Native?
You can use `console.log`, `console.warn`, etc. As of React Native v0.29 you can simply run the following to see logs in the console:
```
$ react-native log-ios
$ react-native log-android
```
**[⬆ Back to Top](#table-of-contents)**
191. ### How to debug your React Native?
Follow the below steps to debug React Native app:
1. Run your application in the iOS simulator.
2. Press `Command + D` and a webpage should open up at `http://localhost:8081/debugger-ui`.
3. Enable _Pause On Caught Exceptions_ for a better debugging experience.
4. Press `Command + Option + I` to open the Chrome Developer tools, or open it via `View` -> `Developer` -> `Developer Tools`.
5. You should now be able to debug as you normally would.
## React supported libraries & Integration
**[⬆ Back to Top](#table-of-contents)**
192. ### What is reselect and how it works?
_Reselect_ is a **selector library** (for Redux) which uses _memoization_ concept. It was originally written to compute derived data from Redux-like applications state, but it can't be tied to any architecture or library.
Reselect keeps a copy of the last inputs/outputs of the last call, and recomputes the result only if one of the inputs changes. If the the same inputs are provided twice in a row, Reselect returns the cached output. It's memoization and cache are fully customizable.
**[⬆ Back to Top](#table-of-contents)**
193. ### What is Flow?
_Flow_ is a _static type checker_ designed to find type errors in JavaScript. Flow types can express much more fine-grained distinctions than traditional type systems. For example, Flow helps you catch errors involving `null`, unlike most type systems.
**[⬆ Back to Top](#table-of-contents)**
194. ### What is the difference between Flow and PropTypes?
Flow is a _static analysis tool_ (static checker) which uses a superset of the language, allowing you to add type annotations to all of your code and catch an entire class of bugs at compile time.
PropTypes is a _basic type checker_ (runtime checker) which has been patched onto React. It can't check anything other than the types of the props being passed to a given component. If you want more flexible typechecking for your entire project Flow/TypeScript are appropriate choices.
**[⬆ Back to Top](#table-of-contents)**
195. ### How to use Font Awesome icons in React?
The below steps followed to include Font Awesome in React:
1. Install `font-awesome`:
```console
$ npm install --save font-awesome
```
2. Import `font-awesome` in your `index.js` file:
```javascript
import "font-awesome/css/font-awesome.min.css";
```
3. Add Font Awesome classes in `className`:
```javascript
render() {
return <div><i className={'fa fa-spinner'} /></div>
}
```
**[⬆ Back to Top](#table-of-contents)**
196. ### What is React Dev Tools?
_React Developer Tools_ let you inspect the component hierarchy, including component props and state. It exists both as a browser extension (for Chrome and Firefox), and as a standalone app (works with other environments including Safari, IE, and React Native).
The official extensions available for different browsers or environments.
1. **Chrome extension**
2. **Firefox extension**
3. **Standalone app** (Safari, React Native, etc)
**[⬆ Back to Top](#table-of-contents)**
197. ### Why is DevTools not loading in Chrome for local files?
If you opened a local HTML file in your browser (`file://...`) then you must first open _Chrome Extensions_ and check `Allow access to file URLs`.
**[⬆ Back to Top](#table-of-contents)**
198. ### How to use Polymer in React?
You need to follow below steps to use Polymer in React,
1. Create a Polymer element:
```jsx harmony
<link
rel="import"
href="../../bower_components/polymer/polymer.html"
/>;
Polymer({
is: "calendar-element",
ready: function () {
this.textContent = "I am a calendar";
},
});
```
2. Create the Polymer component HTML tag by importing it in a HTML document, e.g. import it in the `index.html` of your React application:
```html
<link
rel="import"
href="./src/polymer-components/calendar-element.html"
/>
```
3. Use that element in the JSX file:
```javascript
import React from "react";
class MyComponent extends React.Component {
render() {
return <calendar-element />;
}
}
export default MyComponent;
```
**[⬆ Back to Top](#table-of-contents)**
199. ### What are the advantages of React over Vue.js?
React has the following advantages over Vue.js:
1. Gives more flexibility in large apps developing.
2. Easier to test.
3. Suitable for mobile apps creating.
4. More information and solutions available.
**Note:** The above list of advantages are purely opinionated and it vary based on the professional experience. But they are helpful as base parameters.
**[⬆ Back to Top](#table-of-contents)**
200. ### What is the difference between React and Angular?
Let's see the difference between React and Angular in a table format.
| React | Angular |
| ------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| React is a library and has only the View layer | Angular is a framework and has complete MVC functionality |
| React handles rendering on the server side | AngularJS renders only on the client side but Angular 2 and above renders on the server side |
| React uses JSX that looks like HTML in JS which can be confusing | Angular follows the template approach for HTML, which makes code shorter and easy to understand |
| React Native, which is a React type to build mobile applications are faster and more stable | Ionic, Angular's mobile native app is relatively less stable and slower |
| In React, data flows only in one way and hence debugging is easy | In Angular, data flows both way i.e it has two-way data binding between children and parent and hence debugging is often difficult |
**Note:** The above list of differences are purely opinionated and it vary based on the professional experience. But they are helpful as base parameters.
**[⬆ Back to Top](#table-of-contents)**
201. ### Why React tab is not showing up in DevTools?
When the page loads, _React DevTools_ sets a global named `__REACT_DEVTOOLS_GLOBAL_HOOK__`, then React communicates with that hook during initialization. If the website is not using React or if React fails to communicate with DevTools then it won't show up the tab.
**[⬆ Back to Top](#table-of-contents)**
202. ### What are Styled Components?
`styled-components` is a JavaScript library for styling React applications. It removes the mapping between styles and components, and lets you write actual CSS augmented with JavaScript.
**[⬆ Back to Top](#table-of-contents)**
203. ### Give an example of Styled Components?
Lets create `<Title>` and `<Wrapper>` components with specific styles for each.
```javascript
import React from "react";
import styled from "styled-components";
// Create a <Title> component that renders an <h1> which is centered, red and sized at 1.5em
const Title = styled.h1`
font-size: 1.5em;
text-align: center;
color: palevioletred;
`;
// Create a <Wrapper> component that renders a <section> with some padding and a papayawhip background
const Wrapper = styled.section`
padding: 4em;
background: papayawhip;
`;
```
These two variables, `Title` and `Wrapper`, are now components that you can render just like any other react component.
```jsx harmony
<Wrapper>
<Title>{"Lets start first styled component!"}</Title>
</Wrapper>
```
**[⬆ Back to Top](#table-of-contents)**
204. ### What is Relay?
Relay is a JavaScript framework for providing a data layer and client-server communication to web applications using the React view layer.
**[⬆ Back to Top](#table-of-contents)**
205. ### How to use TypeScript in `create-react-app` application?
Starting from react-scripts@2.1.0 or higher, there is a built-in support for typescript. i.e, `create-react-app` now supports typescript natively. You can just pass `--typescript` option as below
```bash
npx create-react-app my-app --typescript
# or
yarn create react-app my-app --typescript
```
But for lower versions of react scripts, just supply `--scripts-version` option as `react-scripts-ts` while you create a new project. `react-scripts-ts` is a set of adjustments to take the standard `create-react-app` project pipeline and bring TypeScript into the mix.
Now the project layout should look like the following:
```
my-app/
├─ .gitignore
├─ images.d.ts
├─ node_modules/
├─ public/
├─ src/
│ └─ ...
├─ package.json
├─ tsconfig.json
├─ tsconfig.prod.json
├─ tsconfig.test.json
└─ tslint.json
```
## Miscellaneous
**[⬆ Back to Top](#table-of-contents)**
206. ### What are the main features of Reselect library?
Let's see the main features of Reselect library,
1. Selectors can compute derived data, allowing Redux to store the minimal possible state.
2. Selectors are efficient. A selector is not recomputed unless one of its arguments changes.
3. Selectors are composable. They can be used as input to other selectors.
207. #### Give an example of Reselect usage?
Let's take calculations and different amounts of a shipment order with the simplified usage of Reselect:
```javascript
import { createSelector } from "reselect";
const shopItemsSelector = (state) => state.shop.items;
const taxPercentSelector = (state) => state.shop.taxPercent;
const subtotalSelector = createSelector(shopItemsSelector, (items) =>
items.reduce((acc, item) => acc + item.value, 0)
);
const taxSelector = createSelector(
subtotalSelector,
taxPercentSelector,
(subtotal, taxPercent) => subtotal * (taxPercent / 100)
);
export const totalSelector = createSelector(
subtotalSelector,
taxSelector,
(subtotal, tax) => ({ total: subtotal + tax })
);
let exampleState = {
shop: {
taxPercent: 8,
items: [
{ name: "apple", value: 1.2 },
{ name: "orange", value: 0.95 },
],
},
};
console.log(subtotalSelector(exampleState)); // 2.15
console.log(taxSelector(exampleState)); // 0.172
console.log(totalSelector(exampleState)); // { total: 2.322 }
```
**[⬆ Back to Top](#table-of-contents)**
209. ### Does the statics object work with ES6 classes in React?
No, `statics` only works with `React.createClass()`:
```javascript
someComponent = React.createClass({
statics: {
someMethod: function () {
// ..
},
},
});
```
But you can write statics inside ES6+ classes as below,
```javascript
class Component extends React.Component {
static propTypes = {
// ...
};
static someMethod() {
// ...
}
}
```
or writing them outside class as below,
```javascript
class Component extends React.Component {
....
}
Component.propTypes = {...}
Component.someMethod = function(){....}
```
**[⬆ Back to Top](#table-of-contents)**
210. ### Can Redux only be used with React?
Redux can be used as a data store for any UI layer. The most common usage is with React and React Native, but there are bindings available for Angular, Angular 2, Vue, Mithril, and more. Redux simply provides a subscription mechanism which can be used by any other code.
**[⬆ Back to Top](#table-of-contents)**
211. ### Do you need to have a particular build tool to use Redux?
Redux is originally written in ES6 and transpiled for production into ES5 with Webpack and Babel. You should be able to use it regardless of your JavaScript build process. Redux also offers a UMD build that can be used directly without any build process at all.
**[⬆ Back to Top](#table-of-contents)**
212. ### How Redux Form `initialValues` get updated from state?
You need to add `enableReinitialize : true` setting.
```javascript
const InitializeFromStateForm = reduxForm({
form: "initializeFromState",
enableReinitialize: true,
})(UserEdit);
```
If your `initialValues` prop gets updated, your form will update too.
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213. ### How React PropTypes allow different types for one prop?
You can use `oneOfType()` method of `PropTypes`.
For example, the height property can be defined with either `string` or `number` type as below:
```javascript
Component.propTypes = {
size: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
};
```
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214. ### Can I import an SVG file as react component?
You can import SVG directly as component instead of loading it as a file. This feature is available with `react-scripts@2.0.0` and higher.
```jsx harmony
import { ReactComponent as Logo } from "./logo.svg";
const App = () => (
<div>
{/* Logo is an actual react component */}
<Logo />
</div>
);
```
**Note**: Don't forget about the curly braces in the import.
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215. ### Why are inline ref callbacks or functions not recommended?
If the ref callback is defined as an inline function, it will get called twice during updates, first with null and then again with the DOM element. This is because a new instance of the function is created with each render, so React needs to clear the old ref and set up the new one.
```jsx
class UserForm extends Component {
handleSubmit = () => {
console.log("Input Value is: ", this.input.value);
};
render() {
return (
<form onSubmit={this.handleSubmit}>
<input type="text" ref={(input) => (this.input = input)} /> //
Access DOM input in handle submit
<button type="submit">Submit</button>
</form>
);
}
}
```
But our expectation is for the ref callback to get called once, when the component mounts. One quick fix is to use the ES7 class property syntax to define the function
```jsx
class UserForm extends Component {
handleSubmit = () => {
console.log("Input Value is: ", this.input.value);
};
setSearchInput = (input) => {
this.input = input;
};
render() {
return (
<form onSubmit={this.handleSubmit}>
<input type="text" ref={this.setSearchInput} /> // Access DOM input
in handle submit
<button type="submit">Submit</button>
</form>
);
}
}
```
**Note:** In React v16.3,
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216. ### What is render hijacking in react?
The concept of render hijacking is the ability to control what a component will output from another component. It means that you decorate your component by wrapping it into a Higher-Order component. By wrapping, you can inject additional props or make other changes, which can cause changing logic of rendering. It does not actually enable hijacking, but by using HOC you make your component behave differently.
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217. ### What are HOC factory implementations?
There are two main ways of implementing HOCs in React.
1. Props Proxy (PP) and
2. Inheritance Inversion (II).
But they follow different approaches for manipulating the _WrappedComponent_.
**Props Proxy**
In this approach, the render method of the HOC returns a React Element of the type of the WrappedComponent. We also pass through the props that the HOC receives, hence the name **Props Proxy**.
```jsx
function ppHOC(WrappedComponent) {
return class PP extends React.Component {
render() {
return <WrappedComponent {...this.props} />;
}
};
}
```
**Inheritance Inversion**
In this approach, the returned HOC class (Enhancer) extends the WrappedComponent. It is called Inheritance Inversion because instead of the WrappedComponent extending some Enhancer class, it is passively extended by the Enhancer. In this way the relationship between them seems **inverse**.
```jsx
function iiHOC(WrappedComponent) {
return class Enhancer extends WrappedComponent {
render() {
return super.render();
}
};
}
```
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218. ### How to pass numbers to React component?
You should be passing the numbers via curly braces({}) where as strings in quotes
```jsx
React.render(
<User age={30} department={"IT"} />,
document.getElementById("container")
);
```
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219. ### Do I need to keep all my state into Redux? Should I ever use react internal state?
It is up to the developer's decision, i.e., it is developer's job to determine what kinds of state make up your application, and where each piece of state should live. Some users prefer to keep every single piece of data in Redux, to maintain a fully serializable and controlled version of their application at all times. Others prefer to keep non-critical or UI state, such as “is this dropdown currently open”, inside a component's internal state.
Below are the thumb rules to determine what kind of data should be put into Redux
1. Do other parts of the application care about this data?
2. Do you need to be able to create further derived data based on this original data?
3. Is the same data being used to drive multiple components?
4. Is there value to you in being able to restore this state to a given point in time (ie, time travel debugging)?
5. Do you want to cache the data (i.e, use what's in state if it's already there instead of re-requesting it)?
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220. ### What is the purpose of registerServiceWorker in React?
React creates a service worker for you without any configuration by default. The service worker is a web API that helps you cache your assets and other files so that when the user is offline or on a slow network, he/she can still see results on the screen, as such, it helps you build a better user experience, that's what you should know about service worker for now. It's all about adding offline capabilities to your site.
```jsx
import React from "react";
import ReactDOM from "react-dom";
import App from "./App";
import registerServiceWorker from "./registerServiceWorker";
ReactDOM.render(<App />, document.getElementById("root"));
registerServiceWorker();
```
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221. ### What is React memo function?
Class components can be restricted from re-rendering when their input props are the same using **PureComponent or shouldComponentUpdate**. Now you can do the same with function components by wrapping them in **React.memo**.
```jsx
const MyComponent = React.memo(function MyComponent(props) {
/* only rerenders if props change */
});
```
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222. ### What is React lazy function?
The `React.lazy` function lets you render a dynamic import as a regular component. It will automatically load the bundle containing the `OtherComponent` when the component gets rendered. This must return a Promise which resolves to a module with a default export containing a React component.
```jsx
const OtherComponent = React.lazy(() => import("./OtherComponent"));
function MyComponent() {
return (
<div>
<OtherComponent />
</div>
);
}
```
**Note:**
`React.lazy` and `Suspense` is not yet available for server-side rendering. If you want to do code-splitting in a server rendered app, we still recommend React Loadable.
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223. ### How to prevent unnecessary updates using setState?
You can compare the current value of the state with an existing state value and decide whether to rerender the page or not. If the values are the same then you need to return **null** to stop re-rendering otherwise return the latest state value.
For example, the user profile information is conditionally rendered as follows,
```jsx
getUserProfile = (user) => {
const latestAddress = user.address;
this.setState((state) => {
if (state.address === latestAddress) {
return null;
} else {
return { title: latestAddress };
}
});
};
```
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224. ### How do you render Array, Strings and Numbers in React 16 Version?
**Arrays**: Unlike older releases, you don't need to make sure **render** method return a single element in React16. You are able to return multiple sibling elements without a wrapping element by returning an array.
For example, let us take the below list of developers,
```jsx
const ReactJSDevs = () => {
return [
<li key="1">John</li>,
<li key="2">Jackie</li>,
<li key="3">Jordan</li>,
];
};
```
You can also merge this array of items in another array component.
```jsx
const JSDevs = () => {
return (
<ul>
<li>Brad</li>
<li>Brodge</li>
<ReactJSDevs />
<li>Brandon</li>
</ul>
);
};
```
**Strings and Numbers:** You can also return string and number type from the render method.
```jsx
render() {
return 'Welcome to ReactJS questions';
}
// Number
render() {
return 2018;
}
```
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225. ### How to use class field declarations syntax in React classes?
React Class Components can be made much more concise using the class field declarations. You can initialize the local state without using the constructor and declare class methods by using arrow functions without the extra need to bind them.
Let's take a counter example to demonstrate class field declarations for state without using constructor and methods without binding,
```jsx
class Counter extends Component {
state = { value: 0 };
handleIncrement = () => {
this.setState((prevState) => ({
value: prevState.value + 1,
}));
};
handleDecrement = () => {
this.setState((prevState) => ({
value: prevState.value - 1,
}));
};
render() {
return (
<div>
{this.state.value}
<button onClick={this.handleIncrement}>+</button>
<button onClick={this.handleDecrement}>-</button>
</div>
);
}
}
```
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226. ### What are hooks?
Hooks is a special JavaScript function that allows you use state and other React features without writing a class. This pattern has been introduced as a new feature in React 16.8 and helped to isolate the stateful logic from the components.
Let's see an example of useState hook:
```jsx
import { useState } from "react";
function Example() {
// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
return (
<>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>Click me</button>
</>
);
}
```
**Note:** Hooks can be used inside an existing function component without rewriting the component.
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227. ### What rules need to be followed for hooks?
You need to follow two rules in order to use hooks,
1. **Call Hooks only at the top level of your react functions:** You shouldn’t call Hooks inside loops, conditions, or nested functions. This will ensure that Hooks are called in the same order each time a component renders and it preserves the state of Hooks between multiple useState and useEffect calls.
2. **Call Hooks from React Functions only:** You shouldn’t call Hooks from regular JavaScript functions. Instead, you should call them from either function components or custom hooks.
The eslint plugin named **eslint-plugin-react-hooks** can be used to enforce these two rules.
**[⬆ Back to Top](#table-of-contents)**
228. ### How to ensure hooks followed the rules in your project?
React team released an ESLint plugin called **eslint-plugin-react-hooks** that enforces these two rules. You can add this plugin to your project using the below command,
```javascript
npm install eslint-plugin-react-hooks@next
```
And apply the below config in your ESLint config file,
```javascript
// Your ESLint configuration
{
"plugins": [
// ...
"react-hooks"
],
"rules": {
// ...
"react-hooks/rules-of-hooks": "error"
}
}
```
For example, the linter enforce proper naming convention for hooks. If you rename your custom hooks which as prefix "use" to something else then linter won't allow you to call built-in hooks such as useState, useEffect etc inside of your custom hook anymore.
**Note:** This plugin is intended to use in Create React App by default.
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229. ### What are the differences between Flux and Redux?
Below are the major differences between Flux and Redux
| Flux | Redux |
| ---------------------------------------------- | ------------------------------------------ |
| State is mutable | State is immutable |
| The Store contains both state and change logic | The Store and change logic are separate |
| There are multiple stores exist | There is only one store exist |
| All the stores are disconnected and flat | Single store with hierarchical reducers |
| It has a singleton dispatcher | There is no concept of dispatcher |
| React components subscribe to the store | Container components uses connect function |
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230. ### What are the benefits of React Router V4?
Below are the main benefits of React Router V4 module,
1. In React Router v4(version 4), the API is completely about components. A router can be visualized as a single component(`<BrowserRouter>`) which wraps specific child router components(`<Route>`).
2. You don't need to manually set history. The router module will take care history by wrapping routes with `<BrowserRouter>` component.
3. The application size is reduced by adding only the specific router module(Web, core, or native)
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231. ### Can you describe about componentDidCatch lifecycle method signature?
The **componentDidCatch** lifecycle method is invoked after an error has been thrown by a descendant component. The method receives two parameters,
1. error: - The error object which was thrown
2. info: - An object with a componentStack key contains the information about which component threw the error.
The method structure would be as follows
```javascript
componentDidCatch(error, info);
```
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232. ### In which scenarios error boundaries do not catch errors?
Below are the cases in which error boundaries doesn't work,
1. Inside Event handlers
2. Asynchronous code using **setTimeout or requestAnimationFrame** callbacks
3. During Server side rendering
4. When errors thrown in the error boundary code itself
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233. ### Why do you not need error boundaries for event handlers?
Error boundaries do not catch errors inside event handlers.
React doesn’t need error boundaries to recover from errors in event handlers. Unlike the render method and lifecycle methods, the event handlers don’t happen during rendering. So if they throw, React still knows what to display on the screen.
If you need to catch an error inside an event handler, use the regular JavaScript try / catch statement:
```javascript
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = { error: null };
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
try {
// Do something that could throw
} catch (error) {
this.setState({ error });
}
}
render() {
if (this.state.error) {
return <h1>Caught an error.</h1>;
}
return <button onClick={this.handleClick}>Click Me</button>;
}
}
```
Note that the above example is demonstrating regular JavaScript behavior and doesn’t use error boundaries.
**[⬆ Back to Top](#table-of-contents)**
234. ### What is the difference between try catch block and error boundaries?
Try catch block works with imperative code whereas error boundaries are meant for declarative code to render on the screen.
For example, the try catch block used for below imperative code
```javascript
try {
showButton();
} catch (error) {
// ...
}
```
Whereas error boundaries wrap declarative code as below,
```javascript
<ErrorBoundary>
<MyComponent />
</ErrorBoundary>
```
So if an error occurs in a **componentDidUpdate** method caused by a **setState** somewhere deep in the tree, it will still correctly propagate to the closest error boundary.
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235. ### What is the behavior of uncaught errors in react 16?
In React 16, errors that were not caught by any error boundary will result in unmounting of the whole React component tree. The reason behind this decision is that it is worse to leave corrupted UI in place than to completely remove it. For example, it is worse for a payments app to display a wrong amount than to render nothing.
**[⬆ Back to Top](#table-of-contents)**
236. ### What is the proper placement for error boundaries?
The granularity of error boundaries usage is up to the developer based on project needs. You can follow either of these approaches,
1. You can wrap top-level route components to display a generic error message for the entire application.
2. You can also wrap individual components in an error boundary to protect them from crashing the rest of the application.
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237. ### What is the benefit of component stack trace from error boundary?
Apart from error messages and javascript stack, React16 will display the component stack trace with file names and line numbers using error boundary concept.
For example, BuggyCounter component displays the component stack trace as below,
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238. ### What is the required method to be defined for a class component?
The `render()` method is the only required method in a class component. i.e, All methods other than render method are optional for a class component.
**[⬆ Back to Top](#table-of-contents)**
239. ### What are the possible return types of render method?
Below are the list of following types used and return from render method,
1. **React elements:** Elements that instruct React to render a DOM node. It includes html elements such as `<div/>` and user defined elements.
2. **Arrays and fragments:** Return multiple elements to render as Arrays and Fragments to wrap multiple elements
3. **Portals:** Render children into a different DOM subtree.
4. **String and numbers:** Render both Strings and Numbers as text nodes in the DOM
5. **Booleans or null:** Doesn't render anything but these types are used to conditionally render content.
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240. ### What is the main purpose of constructor?
The constructor is mainly used for two purposes,
1. To initialize local state by assigning object to this.state
2. For binding event handler methods to the instance
For example, the below code covers both the above cases,
```javascript
constructor(props) {
super(props);
// Don't call this.setState() here!
this.state = { counter: 0 };
this.handleClick = this.handleClick.bind(this);
}
```
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241. ### Is it mandatory to define constructor for React component?
No, it is not mandatory. i.e, If you don’t initialize state and you don’t bind methods, you don’t need to implement a constructor for your React component.
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242. ### What are default props?
The _defaultProps_ can be defined as a property on the component to set the default values for the props. These default props are used when props not supplied(i.e., undefined props), but not for null props. That means, If you provide null value then it remains null value.
For example, let us create color default prop for the button component,
```javascript
function MyButton {
// ...
}
MyButton.defaultProps = {
color: "red",
};
```
If `props.color` is not provided then it will set the default value to 'red'. i.e, Whenever you try to access the color prop it uses the default value
```javascript
render() {
return <MyButton /> ; // props.color will contain red value
}
```
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243. ### Why should not call setState in componentWillUnmount?
You should not call `setState()` in `componentWillUnmount()` because once a component instance is unmounted, it will never be mounted again.
**[⬆ Back to Top](#table-of-contents)**
244. ### What is the purpose of getDerivedStateFromError?
This lifecycle method is invoked after an error has been thrown by a descendant component. It receives the error that was thrown as a parameter and should return a value to update state.
The signature of the lifecycle method is as follows,
```javascript
static getDerivedStateFromError(error)
```
Let us take error boundary use case with the above lifecycle method for demonstration purpose,
```javascript
class ErrorBoundary extends React.Component {
constructor(props) {
super(props);
this.state = { hasError: false };
}
static getDerivedStateFromError(error) {
// Update state so the next render will show the fallback UI.
return { hasError: true };
}
render() {
if (this.state.hasError) {
// You can render any custom fallback UI
return <h1>Something went wrong.</h1>;
}
return this.props.children;
}
}
```
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245. ### What is the methods order when component re-rendered?
An update can be caused by changes to props or state. The below methods are called in the following order when a component is being re-rendered.
1. static getDerivedStateFromProps()
2. shouldComponentUpdate()
3. render()
4. getSnapshotBeforeUpdate()
5. componentDidUpdate()
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246. ### What are the methods invoked during error handling?
Below methods are called when there is an error during rendering, in a lifecycle method, or in the constructor of any child component.
1. static getDerivedStateFromError()
2. componentDidCatch()
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247. ### What is the purpose of displayName class property?
The displayName string is used in debugging messages. Usually, you don’t need to set it explicitly because it’s inferred from the name of the function or class that defines the component. You might want to set it explicitly if you want to display a different name for debugging purposes or when you create a higher-order component.
For example, To ease debugging, choose a display name that communicates that it’s the result of a withSubscription HOC.
```javascript
function withSubscription(WrappedComponent) {
class WithSubscription extends React.Component {
/* ... */
}
WithSubscription.displayName = `WithSubscription(${getDisplayName(
WrappedComponent
)})`;
return WithSubscription;
}
function getDisplayName(WrappedComponent) {
return (
WrappedComponent.displayName || WrappedComponent.name || "Component"
);
}
```
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248. ### What is the browser support for react applications?
React supports all popular browsers, including Internet Explorer 9 and above, although some polyfills are required for older browsers such as IE 9 and IE 10. If you use **es5-shim and es5-sham** polyfill then it even support old browsers that doesn't support ES5 methods.
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249. ### What is the purpose of unmountComponentAtNode method?
This method is available from react-dom package and it removes a mounted React component from the DOM and clean up its event handlers and state. If no component was mounted in the container, calling this function does nothing. Returns true if a component was unmounted and false if there was no component to unmount.
The method signature would be as follows,
```javascript
ReactDOM.unmountComponentAtNode(container);
```
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250. ### What is code-splitting?
Code-Splitting is a feature supported by bundlers like Webpack and Browserify which can create multiple bundles that can be dynamically loaded at runtime. The react project supports code splitting via dynamic import() feature.
For example, in the below code snippets, it will make moduleA.js and all its unique dependencies as a separate chunk that only loads after the user clicks the 'Load' button.
**moduleA.js**
```javascript
const moduleA = "Hello";
export { moduleA };
```
**App.js**
```javascript
import React, { Component } from "react";
class App extends Component {
handleClick = () => {
import("./moduleA")
.then(({ moduleA }) => {
// Use moduleA
})
.catch((err) => {
// Handle failure
});
};
render() {
return (
<div>
<button onClick={this.handleClick}>Load</button>
</div>
);
}
}
export default App;
```
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252. ### What are Keyed Fragments?
The Fragments declared with the explicit <React.Fragment> syntax may have keys. The general use case is mapping a collection to an array of fragments as below,
```javascript
function Glossary(props) {
return (
<dl>
{props.items.map((item) => (
// Without the `key`, React will fire a key warning
<React.Fragment key={item.id}>
<dt>{item.term}</dt>
<dd>{item.description}</dd>
</React.Fragment>
))}
</dl>
);
}
```
**Note:** key is the only attribute that can be passed to Fragment. In the future, there might be a support for additional attributes, such as event handlers.
**[⬆ Back to Top](#table-of-contents)**
253. ### Does React support all HTML attributes?
As of React 16, both standard or custom DOM attributes are fully supported. Since React components often take both custom and DOM-related props, React uses the camelCase convention just like the DOM APIs.
Let us take few props with respect to standard HTML attributes,
```javascript
<div tabIndex="-1" /> // Just like node.tabIndex DOM API
<div className="Button" /> // Just like node.className DOM API
<input readOnly={true} /> // Just like node.readOnly DOM API
```
These props work similarly to the corresponding HTML attributes, with the exception of the special cases. It also support all SVG attributes.
**[⬆ Back to Top](#table-of-contents)**
254. ### What are the limitations with HOCs?
Higher-order components come with a few caveats apart from its benefits. Below are the few listed in an order,
1. **Don’t use HOCs inside the render method:**
It is not recommended to apply a HOC to a component within the render method of a component.
```javascript
render() {
// A new version of EnhancedComponent is created on every render
// EnhancedComponent1 !== EnhancedComponent2
const EnhancedComponent = enhance(MyComponent);
// That causes the entire subtree to unmount/remount each time!
return <EnhancedComponent />;
}
```
The above code impacts on performance by remounting a component that causes the state of that component and all of its children to be lost. Instead, apply HOCs outside the component definition so that the resulting component is created only once.
2. **Static methods must be copied over:**
When you apply a HOC to a component the new component does not have any of the static methods of the original component
```javascript
// Define a static method
WrappedComponent.staticMethod = function () {
/*...*/
};
// Now apply a HOC
const EnhancedComponent = enhance(WrappedComponent);
// The enhanced component has no static method
typeof EnhancedComponent.staticMethod === "undefined"; // true
```
You can overcome this by copying the methods onto the container before returning it,
```javascript
function enhance(WrappedComponent) {
class Enhance extends React.Component {
/*...*/
}
// Must know exactly which method(s) to copy :(
Enhance.staticMethod = WrappedComponent.staticMethod;
return Enhance;
}
```
3. **Refs aren’t passed through:**
For HOCs you need to pass through all props to the wrapped component but this does not work for refs. This is because ref is not really a prop similar to key. In this case you need to use the React.forwardRef API
**[⬆ Back to Top](#table-of-contents)**
255. ### How to debug forwardRefs in DevTools?
**React.forwardRef** accepts a render function as parameter and DevTools uses this function to determine what to display for the ref forwarding component.
For example, If you don't name the render function or not using displayName property then it will appear as ”ForwardRef” in the DevTools,
```javascript
const WrappedComponent = React.forwardRef((props, ref) => {
return <LogProps {...props} forwardedRef={ref} />;
});
```
But If you name the render function then it will appear as **”ForwardRef(myFunction)”**
```javascript
const WrappedComponent = React.forwardRef(function myFunction(props, ref) {
return <LogProps {...props} forwardedRef={ref} />;
});
```
As an alternative, You can also set displayName property for forwardRef function,
```javascript
function logProps(Component) {
class LogProps extends React.Component {
// ...
}
function forwardRef(props, ref) {
return <LogProps {...props} forwardedRef={ref} />;
}
// Give this component a more helpful display name in DevTools.
// e.g. "ForwardRef(logProps(MyComponent))"
const name = Component.displayName || Component.name;
forwardRef.displayName = `logProps(${name})`;
return React.forwardRef(forwardRef);
}
```
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256. ### When component props defaults to true?
If you pass no value for a prop, it defaults to true. This behavior is available so that it matches the behavior of HTML.
For example, below expressions are equivalent,
```javascript
<MyInput autocomplete />
<MyInput autocomplete={true} />
```
**Note:** It is not recommended to use this approach because it can be confused with the ES6 object shorthand (example, `{name}` which is short for `{name: name}`)
**[⬆ Back to Top](#table-of-contents)**
257. ### What is NextJS and major features of it?
Next.js is a popular and lightweight framework for static and server‑rendered applications built with React. It also provides styling and routing solutions. Below are the major features provided by NextJS,
1. Server-rendered by default
2. Automatic code splitting for faster page loads
3. Simple client-side routing (page based)
4. Webpack-based dev environment which supports (HMR)
5. Able to implement with Express or any other Node.js HTTP server
6. Customizable with your own Babel and Webpack configurations
**[⬆ Back to Top](#table-of-contents)**
258. ### How do you pass an event handler to a component?
You can pass event handlers and other functions as props to child components. It can be used in child component as below,
```html
<button onClick="{this.handleClick}"></button>
```
**[⬆ Back to Top](#table-of-contents)**
259. ### Is it good to use arrow functions in render methods?
Yes, You can use. It is often the easiest way to pass parameters to callback functions. But you need to optimize the performance while using it.
```javascript
class Foo extends Component {
handleClick() {
console.log("Click happened");
}
render() {
return <button onClick={() => this.handleClick()}>Click Me</button>;
}
}
```
**Note:** Using an arrow function in render method creates a new function each time the component renders, which may have performance implications
**[⬆ Back to Top](#table-of-contents)**
260. ### How to prevent a function from being called multiple times?
If you use an event handler such as **onClick or onScroll** and want to prevent the callback from being fired too quickly, then you can limit the rate at which callback is executed. This can be achieved in the below possible ways,
1. **Throttling:** Changes based on a time based frequency. For example, it can be used using \_.throttle lodash function
2. **Debouncing:** Publish changes after a period of inactivity. For example, it can be used using \_.debounce lodash function
3. **RequestAnimationFrame throttling:** Changes based on requestAnimationFrame. For example, it can be used using raf-schd lodash function
**[⬆ Back to Top](#table-of-contents)**
261. ### How JSX prevents Injection Attacks?
React DOM escapes any values embedded in JSX before rendering them. Thus it ensures that you can never inject anything that’s not explicitly written in your application. Everything is converted to a string before being rendered.
For example, you can embed user input as below,
```javascript
const name = response.potentiallyMaliciousInput;
const element = <h1>{name}</h1>;
```
This way you can prevent XSS(Cross-site-scripting) attacks in the application.
**[⬆ Back to Top](#table-of-contents)**
262. ### How do you update rendered elements?
You can update UI(represented by rendered element) by passing the newly created element to ReactDOM's render method.
For example, lets take a ticking clock example, where it updates the time by calling render method multiple times,
```javascript
function tick() {
const element = (
<div>
<h1>Hello, world!</h1>
<h2>It is {new Date().toLocaleTimeString()}.</h2>
</div>
);
ReactDOM.render(element, document.getElementById("root"));
}
setInterval(tick, 1000);
```
**[⬆ Back to Top](#table-of-contents)**
263. ### How do you say that props are readonly?
When you declare a component as a function or a class, it must never modify its own props.
Let us take a below capital function,
```javascript
function capital(amount, interest) {
return amount + interest;
}
```
The above function is called “pure” because it does not attempt to change their inputs, and always return the same result for the same inputs. Hence, React has a single rule saying "All React components must act like pure functions with respect to their props."
**[⬆ Back to Top](#table-of-contents)**
264. ### How do you say that state updates are merged?
When you call setState() in the component, React merges the object you provide into the current state.
For example, let us take a facebook user with posts and comments details as state variables,
```javascript
constructor(props) {
super(props);
this.state = {
posts: [],
comments: []
};
}
```
Now you can update them independently with separate `setState()` calls as below,
```javascript
componentDidMount() {
fetchPosts().then(response => {
this.setState({
posts: response.posts
});
});
fetchComments().then(response => {
this.setState({
comments: response.comments
});
});
}
```
As mentioned in the above code snippets, `this.setState({comments})` updates only comments variable without modifying or replacing `posts` variable.
**[⬆ Back to Top](#table-of-contents)**
265. ### How do you pass arguments to an event handler?
During iterations or loops, it is common to pass an extra parameter to an event handler. This can be achieved through arrow functions or bind method.
Let us take an example of user details updated in a grid,
```javascript
<button onClick={(e) => this.updateUser(userId, e)}>Update User details</button>
<button onClick={this.updateUser.bind(this, userId)}>Update User details</button>
```
In the both approaches, the synthetic argument `e` is passed as a second argument. You need to pass it explicitly for arrow functions and it will be passed automatically for `bind` method.
**[⬆ Back to Top](#table-of-contents)**
266. ### How to prevent component from rendering?
You can prevent component from rendering by returning null based on specific condition. This way it can conditionally render component.
```javascript
function Greeting(props) {
if (!props.loggedIn) {
return null;
}
return <div className="greeting">welcome, {props.name}</div>;
}
```
```javascript
class User extends React.Component {
constructor(props) {
super(props);
this.state = {loggedIn: false, name: 'John'};
}
render() {
return (
<div>
//Prevent component render if it is not loggedIn
<Greeting loggedIn={this.state.loggedIn} />
<UserDetails name={this.state.name}>
</div>
);
}
```
In the above example, the `greeting` component skips its rendering section by applying condition and returning null value.
**[⬆ Back to Top](#table-of-contents)**
267. ### What are the conditions to safely use the index as a key?
There are three conditions to make sure, it is safe use the index as a key.
1. The list and items are static– they are not computed and do not change
2. The items in the list have no ids
3. The list is never reordered or filtered.
**[⬆ Back to Top](#table-of-contents)**
268. ### Should keys be globally unique?
The keys used within arrays should be unique among their siblings but they don’t need to be globally unique. i.e, You can use the same keys with two different arrays.
For example, the below `Book` component uses two arrays with different arrays,
```javascript
function Book(props) {
const index = (
<ul>
{props.pages.map((page) => (
<li key={page.id}>{page.title}</li>
))}
</ul>
);
const content = props.pages.map((page) => (
<div key={page.id}>
<h3>{page.title}</h3>
<p>{page.content}</p>
<p>{page.pageNumber}</p>
</div>
));
return (
<div>
{index}
<hr />
{content}
</div>
);
}
```
**[⬆ Back to Top](#table-of-contents)**
269. ### What is the popular choice for form handling?
`Formik` is a form library for react which provides solutions such as validation, keeping track of the visited fields, and handling form submission.
In detail, You can categorize them as follows,
1. Getting values in and out of form state
2. Validation and error messages
3. Handling form submission
It is used to create a scalable, performant, form helper with a minimal API to solve annoying stuff.
**[⬆ Back to Top](#table-of-contents)**
270. ### What are the advantages of formik over redux form library?
Below are the main reasons to recommend formik over redux form library,
1. The form state is inherently short-term and local, so tracking it in Redux (or any kind of Flux library) is unnecessary.
2. Redux-Form calls your entire top-level Redux reducer multiple times ON EVERY SINGLE KEYSTROKE. This way it increases input latency for large apps.
3. Redux-Form is 22.5 kB minified gzipped whereas Formik is 12.7 kB
**[⬆ Back to Top](#table-of-contents)**
271. ### Why are you not required to use inheritance?
In React, it is recommended to use composition over inheritance to reuse code between components. Both Props and composition give you all the flexibility you need to customize a component’s look and behavior explicitly and safely.
Whereas, If you want to reuse non-UI functionality between components, it is suggested to extract it into a separate JavaScript module. Later components import it and use that function, object, or class, without extending it.
**[⬆ Back to Top](#table-of-contents)**
272. ### Can I use web components in react application?
Yes, you can use web components in a react application. Even though many developers won't use this combination, it may require especially if you are using third-party UI components that are written using Web Components.
For example, let us use `Vaadin` date picker web component as below,
```javascript
import React, { Component } from "react";
import "./App.css";
import "@vaadin/vaadin-date-picker";
class App extends Component {
render() {
return (
<div className="App">
<vaadin-date-picker label="When were you born?"></vaadin-date-picker>
</div>
);
}
}
export default App;
```
**[⬆ Back to Top](#table-of-contents)**
273. ### What is dynamic import?
You can achieve code-splitting in your app using dynamic import.
Let's take an example of addition,
1. **Normal Import**
```javascript
import { add } from "./math";
console.log(add(10, 20));
```
2. **Dynamic Import**
```javascript
import("./math").then((math) => {
console.log(math.add(10, 20));
});
```
**[⬆ Back to Top](#table-of-contents)**
274. ### What are loadable components?
If you want to do code-splitting in a server rendered app, it is recommend to use Loadable Components because React.lazy and Suspense is not yet available for server-side rendering. Loadable lets you render a dynamic import as a regular component.
Lets take an example,
```javascript
import loadable from "@loadable/component";
const OtherComponent = loadable(() => import("./OtherComponent"));
function MyComponent() {
return (
<div>
<OtherComponent />
</div>
);
}
```
Now OtherComponent will be loaded in a separated bundle
**[⬆ Back to Top](#table-of-contents)**
275. ### What is suspense component?
If the module containing the dynamic import is not yet loaded by the time parent component renders, you must show some fallback content while you’re waiting for it to load using a loading indicator. This can be done using **Suspense** component.
For example, the below code uses suspense component,
```javascript
const OtherComponent = React.lazy(() => import("./OtherComponent"));
function MyComponent() {
return (
<div>
<Suspense fallback={<div>Loading...</div>}>
<OtherComponent />
</Suspense>
</div>
);
}
```
As mentioned in the above code, Suspense is wrapped above the lazy component.
**[⬆ Back to Top](#table-of-contents)**
276. ### What is route based code splitting?
One of the best place to do code splitting is with routes. The entire page is going to re-render at once so users are unlikely to interact with other elements in the page at the same time. Due to this, the user experience won't be disturbed.
Let us take an example of route based website using libraries like React Router with React.lazy,
```javascript
import { BrowserRouter as Router, Route, Switch } from "react-router-dom";
import React, { Suspense, lazy } from "react";
const Home = lazy(() => import("./routes/Home"));
const About = lazy(() => import("./routes/About"));
const App = () => (
<Router>
<Suspense fallback={<div>Loading...</div>}>
<Switch>
<Route exact path="/" component={Home} />
<Route path="/about" component={About} />
</Switch>
</Suspense>
</Router>
);
```
In the above code, the code splitting will happen at each route level.
**[⬆ Back to Top](#table-of-contents)**
277. ### Give an example on How to use context?
**Context** is designed to share data that can be considered **global** for a tree of React components.
For example, in the code below lets manually thread through a “theme” prop in order to style the Button component.
```javascript
//Lets create a context with a default theme value "luna"
const ThemeContext = React.createContext("luna");
// Create App component where it uses provider to pass theme value in the tree
class App extends React.Component {
render() {
return (
<ThemeContext.Provider value="nova">
<Toolbar />
</ThemeContext.Provider>
);
}
}
// A middle component where you don't need to pass theme prop anymore
function Toolbar(props) {
return (
<div>
<ThemedButton />
</div>
);
}
// Lets read theme value in the button component to use
class ThemedButton extends React.Component {
static contextType = ThemeContext;
render() {
return <Button theme={this.context} />;
}
}
```
**[⬆ Back to Top](#table-of-contents)**
278. ### What is the purpose of default value in context?
The defaultValue argument is only used when a component does not have a matching Provider above it in the tree. This can be helpful for testing components in isolation without wrapping them.
Below code snippet provides default theme value as Luna.
```javascript
const MyContext = React.createContext(defaultValue);
```
**[⬆ Back to Top](#table-of-contents)**
279. ### How do you use contextType?
ContextType is used to consume the context object. The contextType property can be used in two ways,
1. **contextType as property of class:**
The contextType property on a class can be assigned a Context object created by React.createContext(). After that, you can consume the nearest current value of that Context type using this.context in any of the lifecycle methods and render function.
Lets assign contextType property on MyClass as below,
```javascript
class MyClass extends React.Component {
componentDidMount() {
let value = this.context;
/* perform a side-effect at mount using the value of MyContext */
}
componentDidUpdate() {
let value = this.context;
/* ... */
}
componentWillUnmount() {
let value = this.context;
/* ... */
}
render() {
let value = this.context;
/* render something based on the value of MyContext */
}
}
MyClass.contextType = MyContext;
```
2. **Static field**
You can use a static class field to initialize your contextType using public class field syntax.
```javascript
class MyClass extends React.Component {
static contextType = MyContext;
render() {
let value = this.context;
/* render something based on the value */
}
}
```
**[⬆ Back to Top](#table-of-contents)**
280. ### What is a consumer?
A Consumer is a React component that subscribes to context changes. It requires a function as a child which receives current context value as argument and returns a react node. The value argument passed to the function will be equal to the value prop of the closest Provider for this context above in the tree.
Lets take a simple example,
```javascript
<MyContext.Consumer>
{value => /* render something based on the context value */}
</MyContext.Consumer>
```
**[⬆ Back to Top](#table-of-contents)**
281. ### How do you solve performance corner cases while using context?
The context uses reference identity to determine when to re-render, there are some gotchas that could trigger unintentional renders in consumers when a provider’s parent re-renders.
For example, the code below will re-render all consumers every time the Provider re-renders because a new object is always created for value.
```javascript
class App extends React.Component {
render() {
return (
<Provider value={{ something: "something" }}>
<Toolbar />
</Provider>
);
}
}
```
This can be solved by lifting up the value to parent state,
```javascript
class App extends React.Component {
constructor(props) {
super(props);
this.state = {
value: { something: "something" },
};
}
render() {
return (
<Provider value={this.state.value}>
<Toolbar />
</Provider>
);
}
}
```
**[⬆ Back to Top](#table-of-contents)**
282. ### What is the purpose of forward ref in HOCs?
Refs will not get passed through because ref is not a prop. It is handled differently by React just like **key**. If you add a ref to a HOC, the ref will refer to the outermost container component, not the wrapped component. In this case, you can use Forward Ref API. For example, we can explicitly forward refs to the inner FancyButton component using the React.forwardRef API.
The below HOC logs all props,
```javascript
function logProps(Component) {
class LogProps extends React.Component {
componentDidUpdate(prevProps) {
console.log("old props:", prevProps);
console.log("new props:", this.props);
}
render() {
const { forwardedRef, ...rest } = this.props;
// Assign the custom prop "forwardedRef" as a ref
return <Component ref={forwardedRef} {...rest} />;
}
}
return React.forwardRef((props, ref) => {
return <LogProps {...props} forwardedRef={ref} />;
});
}
```
Let's use this HOC to log all props that get passed to our “fancy button” component,
```javascript
class FancyButton extends React.Component {
focus() {
// ...
}
// ...
}
export default logProps(FancyButton);
```
Now let's create a ref and pass it to FancyButton component. In this case, you can set focus to button element.
```javascript
import FancyButton from "./FancyButton";
const ref = React.createRef();
ref.current.focus();
<FancyButton label="Click Me" handleClick={handleClick} ref={ref} />;
```
**[⬆ Back to Top](#table-of-contents)**
283. ### Is ref argument available for all functions or class components?
Regular function or class components don’t receive the ref argument, and ref is not available in props either. The second ref argument only exists when you define a component with React.forwardRef call.
**[⬆ Back to Top](#table-of-contents)**
284. ### Why do you need additional care for component libraries while using forward refs?
When you start using forwardRef in a component library, you should treat it as a breaking change and release a new major version of your library. This is because your library likely has a different behavior such as what refs get assigned to, and what types are exported. These changes can break apps and other libraries that depend on the old behavior.
**[⬆ Back to Top](#table-of-contents)**
285. ### How to create react class components without ES6?
If you don’t use ES6 then you may need to use the create-react-class module instead. For default props, you need to define getDefaultProps() as a function on the passed object. Whereas for initial state, you have to provide a separate getInitialState method that returns the initial state.
```javascript
var Greeting = createReactClass({
getDefaultProps: function () {
return {
name: "Jhohn",
};
},
getInitialState: function () {
return { message: this.props.message };
},
handleClick: function () {
console.log(this.state.message);
},
render: function () {
return <h1>Hello, {this.props.name}</h1>;
},
});
```
**Note:** If you use createReactClass then auto binding is available for all methods. i.e, You don't need to use `.bind(this)` with in constructor for event handlers.
**[⬆ Back to Top](#table-of-contents)**
286. ### Is it possible to use react without JSX?
Yes, JSX is not mandatory for using React. Actually it is convenient when you don’t want to set up compilation in your build environment. Each JSX element is just syntactic sugar for calling `React.createElement(component, props, ...children)`.
For example, let us take a greeting example with JSX,
```javascript
class Greeting extends React.Component {
render() {
return <div>Hello {this.props.message}</div>;
}
}
ReactDOM.render(
<Greeting message="World" />,
document.getElementById("root")
);
```
You can write the same code without JSX as below,
```javascript
class Greeting extends React.Component {
render() {
return React.createElement("div", null, `Hello ${this.props.message}`);
}
}
ReactDOM.render(
React.createElement(Greeting, { message: "World" }, null),
document.getElementById("root")
);
```
**[⬆ Back to Top](#table-of-contents)**
287. ### What is diffing algorithm?
React needs to use algorithms to find out how to efficiently update the UI to match the most recent tree. The diffing algorithms is generating the minimum number of operations to transform one tree into another. However, the algorithms have a complexity in the order of O(n³) where n is the number of elements in the tree.
In this case, displaying 1000 elements would require in the order of one billion comparisons. This is far too expensive. Instead, React implements a heuristic O(n) algorithm based on two assumptions:
1. Two elements of different types will produce different trees.
2. The developer can hint at which child elements may be stable across different renders with a key prop.
**[⬆ Back to Top](#table-of-contents)**
288. ### What are the rules covered by diffing algorithm?
When diffing two trees, React first compares the two root elements. The behavior is different depending on the types of the root elements. It covers the below rules during reconciliation algorithm,
1. **Elements Of Different Types:**
Whenever the root elements have different types, React will tear down the old tree and build the new tree from scratch. For example, elements <a> to <img>, or from <Article> to <Comment> of different types lead a full rebuild.
2. **DOM Elements Of The Same Type:**
When comparing two React DOM elements of the same type, React looks at the attributes of both, keeps the same underlying DOM node, and only updates the changed attributes. Lets take an example with same DOM elements except className attribute,
```javascript
<div className="show" title="ReactJS" />
<div className="hide" title="ReactJS" />
```
3. **Component Elements Of The Same Type:**
When a component updates, the instance stays the same, so that state is maintained across renders. React updates the props of the underlying component instance to match the new element, and calls componentWillReceiveProps() and componentWillUpdate() on the underlying instance. After that, the render() method is called and the diff algorithm recurses on the previous result and the new result.
4. **Recursing On Children:**
when recursing on the children of a DOM node, React just iterates over both lists of children at the same time and generates a mutation whenever there’s a difference. For example, when adding an element at the end of the children, converting between these two trees works well.
```javascript
<ul>
<li>first</li>
<li>second</li>
</ul>
<ul>
<li>first</li>
<li>second</li>
<li>third</li>
</ul>
```
5. **Handling keys:**
React supports a key attribute. When children have keys, React uses the key to match children in the original tree with children in the subsequent tree. For example, adding a key can make the tree conversion efficient,
```javascript
<ul>
<li key="2015">Duke</li>
<li key="2016">Villanova</li>
</ul>
<ul>
<li key="2014">Connecticut</li>
<li key="2015">Duke</li>
<li key="2016">Villanova</li>
</ul>
```
**[⬆ Back to Top](#table-of-contents)**
289. ### When do you need to use refs?
There are few use cases to go for refs,
1. Managing focus, text selection, or media playback.
2. Triggering imperative animations.
3. Integrating with third-party DOM libraries.
**[⬆ Back to Top](#table-of-contents)**
290. ### Must prop be named as render for render props?
Even though the pattern named render props, you don’t have to use a prop named render to use this pattern. i.e, Any prop that is a function that a component uses to know what to render is technically a “render prop”. Lets take an example with the children prop for render props,
```javascript
<Mouse
children={(mouse) => (
<p>
The mouse position is {mouse.x}, {mouse.y}
</p>
)}
/>
```
Actually children prop doesn’t need to be named in the list of “attributes” in JSX element. Instead, you can keep it directly inside element,
```javascript
<Mouse>
{(mouse) => (
<p>
The mouse position is {mouse.x}, {mouse.y}
</p>
)}
</Mouse>
```
While using this above technique(without any name), explicitly state that children should be a function in your propTypes.
```javascript
Mouse.propTypes = {
children: PropTypes.func.isRequired,
};
```
**[⬆ Back to Top](#table-of-contents)**
291. ### What are the problems of using render props with pure components?
If you create a function inside a render method, it negates the purpose of pure component. Because the shallow prop comparison will always return false for new props, and each render in this case will generate a new value for the render prop. You can solve this issue by defining the render function as instance method.
**[⬆ Back to Top](#table-of-contents)**
292. ### How do you create HOC using render props?
You can implement most higher-order components (HOC) using a regular component with a render prop. For example, if you would prefer to have a withMouse HOC instead of a <Mouse> component, you could easily create one using a regular <Mouse> with a render prop.
```javascript
function withMouse(Component) {
return class extends React.Component {
render() {
return (
<Mouse
render={(mouse) => <Component {...this.props} mouse={mouse} />}
/>
);
}
};
}
```
This way render props gives the flexibility of using either pattern.
**[⬆ Back to Top](#table-of-contents)**
293. ### What is windowing technique?
Windowing is a technique that only renders a small subset of your rows at any given time, and can dramatically reduce the time it takes to re-render the components as well as the number of DOM nodes created. If your application renders long lists of data then this technique is recommended. Both react-window and react-virtualized are popular windowing libraries which provides several reusable components for displaying lists, grids, and tabular data.
**[⬆ Back to Top](#table-of-contents)**
294. ### How do you print falsy values in JSX?
The falsy values such as false, null, undefined, and true are valid children but they don't render anything. If you still want to display them then you need to convert it to string. Let's take an example on how to convert to a string,
```javascript
<div>My JavaScript variable is {String(myVariable)}.</div>
```
**[⬆ Back to Top](#table-of-contents)**
295. ### What is the typical use case of portals?
React portals are very useful when a parent component has overflow: hidden or has properties that affect the stacking context (e.g. z-index, position, opacity) and you need to visually “break out” of its container.
For example, dialogs, global message notifications, hovercards, and tooltips.
**[⬆ Back to Top](#table-of-contents)**
296. ### How do you set default value for uncontrolled component?
In React, the value attribute on form elements will override the value in the DOM. With an uncontrolled component, you might want React to specify the initial value, but leave subsequent updates uncontrolled. To handle this case, you can specify a **defaultValue** attribute instead of **value**.
```javascript
render() {
return (
<form onSubmit={this.handleSubmit}>
<label>
User Name:
<input
defaultValue="John"
type="text"
ref={this.input} />
</label>
<input type="submit" value="Submit" />
</form>
);
}
```
The same applies for `select` and `textArea` inputs. But you need to use **defaultChecked** for `checkbox` and `radio` inputs.
**[⬆ Back to Top](#table-of-contents)**
297. ### What is your favorite React stack?
Even though the tech stack varies from developer to developer, the most popular stack is used in react boilerplate project code. It mainly uses Redux and redux-saga for state management and asynchronous side-effects, react-router for routing purpose, styled-components for styling react components, axios for invoking REST api, and other supported stack such as webpack, reselect, ESNext, Babel.
You can clone the project https://github.com/react-boilerplate/react-boilerplate and start working on any new react project.
**[⬆ Back to Top](#table-of-contents)**
298. ### What is the difference between Real DOM and Virtual DOM?
Below are the main differences between Real DOM and Virtual DOM,
| Real DOM | Virtual DOM |
| ------------------------------------ | ------------------------------------ |
| Updates are slow | Updates are fast |
| DOM manipulation is very expensive. | DOM manipulation is very easy |
| You can update HTML directly. | You Can’t directly update HTML |
| It causes too much of memory wastage | There is no memory wastage |
| Creates a new DOM if element updates | It updates the JSX if element update |
**[⬆ Back to Top](#table-of-contents)**
299. ### How to add Bootstrap to a react application?
Bootstrap can be added to your React app in a three possible ways,
1. Using the Bootstrap CDN:
This is the easiest way to add bootstrap. Add both bootstrap CSS and JS resources in a head tag.
2. Bootstrap as Dependency:
If you are using a build tool or a module bundler such as Webpack, then this is the preferred option for adding Bootstrap to your React application
```javascript
npm install bootstrap
```
3. React Bootstrap Package:
In this case, you can add Bootstrap to our React app is by using a package that has rebuilt Bootstrap components to work particularly as React components. Below packages are popular in this category,
1. react-bootstrap
2. reactstrap
**[⬆ Back to Top](#table-of-contents)**
300. ### Can you list down top websites or applications using react as front end framework?
Below are the `top 10 websites` using React as their front-end framework,
1. Facebook
2. Uber
3. Instagram
4. WhatsApp
5. Khan Academy
6. Airbnb
7. Dropbox
8. Flipboard
9. Netflix
10. PayPal
**[⬆ Back to Top](#table-of-contents)**
301. ### Is it recommended to use CSS In JS technique in React?
React does not have any opinion about how styles are defined but if you are a beginner then good starting point is to define your styles in a separate \*.css file as usual and refer to them using className. This functionality is not part of React but came from third-party libraries. But If you want to try a different approach(CSS-In-JS) then styled-components library is a good option.
**[⬆ Back to Top](#table-of-contents)**
302. ### Do I need to rewrite all my class components with hooks?
No. But you can try Hooks in a few components(or new components) without rewriting any existing code. Because there are no plans to remove classes in ReactJS.
**[⬆ Back to Top](#table-of-contents)**
303. ### How to fetch data with React Hooks?
The effect hook called `useEffect` can be used to fetch data from an API and to set the data in the local state of the component with the useState hook’s update function.
Here is an example of fetching a list of react articles from an API using fetch.
```javascript
import React from "react";
function App() {
const [data, setData] = React.useState({ hits: [] });
React.useEffect(() => {
fetch("http://hn.algolia.com/api/v1/search?query=react")
.then(response => response.json())
.then(data => setData(data))
}, []);
return (
<ul>
{data.hits.map((item) => (
<li key={item.objectID}>
<a href={item.url}>{item.title}</a>
</li>
))}
</ul>
);
}
export default App;
```
A popular way to simplify this is by using the library axios.
We provided an empty array as second argument to the useEffect hook to avoid activating it on component updates. This way, it only fetches on component mount.
**[⬆ Back to Top](#table-of-contents)**
304. ### Is Hooks cover all use cases for classes?
Hooks doesn't cover all use cases of classes but there is a plan to add them soon. Currently there are no Hook equivalents to the uncommon **getSnapshotBeforeUpdate** and **componentDidCatch** lifecycles yet.
**[⬆ Back to Top](#table-of-contents)**
305. ### What is the stable release for hooks support?
React includes a stable implementation of React Hooks in 16.8 release for below packages
1. React DOM
2. React DOM Server
3. React Test Renderer
4. React Shallow Renderer
**[⬆ Back to Top](#table-of-contents)**
306. ### Why do we use array destructuring (square brackets notation) in `useState`?
When we declare a state variable with `useState`, it returns a pair — an array with two items. The first item is the current value, and the second is a function that updates the value. Using [0] and [1] to access them is a bit confusing because they have a specific meaning. This is why we use array destructuring instead.
For example, the array index access would look as follows:
```javascript
var userStateVariable = useState("userProfile"); // Returns an array pair
var user = userStateVariable[0]; // Access first item
var setUser = userStateVariable[1]; // Access second item
```
Whereas with array destructuring the variables can be accessed as follows:
```javascript
const [user, setUser] = useState("userProfile");
```
**[⬆ Back to Top](#table-of-contents)**
307. ### What are the sources used for introducing hooks?
Hooks got the ideas from several different sources. Below are some of them,
1. Previous experiments with functional APIs in the react-future repository
2. Community experiments with render prop APIs such as Reactions Component
3. State variables and state cells in DisplayScript.
4. Subscriptions in Rx.
5. Reducer components in ReasonReact.
**[⬆ Back to Top](#table-of-contents)**
308. ### How do you access imperative API of web components?
Web Components often expose an imperative API to implement its functions. You will need to use a **ref** to interact with the DOM node directly if you want to access imperative API of a web component. But if you are using third-party Web Components, the best solution is to write a React component that behaves as a **wrapper** for your Web Component.
**[⬆ Back to Top](#table-of-contents)**
309. ### What is formik?
Formik is a small react form library that helps you with the three major problems,
1. Getting values in and out of form state
2. Validation and error messages
3. Handling form submission
**[⬆ Back to Top](#table-of-contents)**
310. ### What are typical middleware choices for handling asynchronous calls in Redux?
Some of the popular middleware choices for handling asynchronous calls in Redux eco system are `Redux Thunk, Redux Promise, Redux Saga`.
**[⬆ Back to Top](#table-of-contents)**
311. ### Do browsers understand JSX code?
No, browsers can't understand JSX code. You need a transpiler to convert your JSX to regular Javascript that browsers can understand. The most widely used transpiler right now is Babel.
**[⬆ Back to Top](#table-of-contents)**
312. ### Describe about data flow in react?
React implements one-way reactive data flow using props which reduce boilerplate and is easier to understand than traditional two-way data binding.
**[⬆ Back to Top](#table-of-contents)**
313. ### What is react scripts?
The `react-scripts` package is a set of scripts from the create-react-app starter pack which helps you kick off projects without configuring. The `react-scripts start` command sets up the development environment and starts a server, as well as hot module reloading.
**[⬆ Back to Top](#table-of-contents)**
314. ### What are the features of create react app?
Below are the list of some of the features provided by create react app.
1. React, JSX, ES6, Typescript and Flow syntax support.
2. Autoprefixed CSS
3. CSS Reset/Normalize
4. A live development server
5. A fast interactive unit test runner with built-in support for coverage reporting
6. A build script to bundle JS, CSS, and images for production, with hashes and sourcemaps
7. An offline-first service worker and a web app manifest, meeting all the Progressive Web App criteria.
**[⬆ Back to Top](#table-of-contents)**
315. ### What is the purpose of renderToNodeStream method?
The `ReactDOMServer#renderToNodeStream` method is used to generate HTML on the server and send the markup down on the initial request for faster page loads. It also helps search engines to crawl your pages easily for SEO purposes.
**Note:** Remember this method is not available in the browser but only server.
**[⬆ Back to Top](#table-of-contents)**
316. ### What is MobX?
MobX is a simple, scalable and battle tested state management solution for applying functional reactive programming (TFRP). For reactJs application, you need to install below packages,
```bash
npm install mobx --save
npm install mobx-react --save
```
**[⬆ Back to Top](#table-of-contents)**
317. ### What are the differences between Redux and MobX?
Below are the main differences between Redux and MobX,
| Topic | Redux | MobX |
| ------------- | ------------------------------------------------------------- | ---------------------------------------------------------------------- |
| Definition | It is a javascript library for managing the application state | It is a library for reactively managing the state of your applications |
| Programming | It is mainly written in ES6 | It is written in JavaScript(ES5) |
| Data Store | There is only one large store exist for data storage | There is more than one store for storage |
| Usage | Mainly used for large and complex applications | Used for simple applications |
| Performance | Need to be improved | Provides better performance |
| How it stores | Uses JS Object to store | Uses observable to store the data |
**[⬆ Back to Top](#table-of-contents)**
318. ### Should I learn ES6 before learning ReactJS?
No, you don’t have to learn es2015/es6 to learn react. But you may find many resources or React ecosystem uses ES6 extensively. Let's see some of the frequently used ES6 features,
1. **Destructuring:** To get props and use them in a component
```javascript
// in es 5
var someData = this.props.someData;
var dispatch = this.props.dispatch;
// in es6
const { someData, dispatch } = this.props;
```
2. Spread operator: Helps in passing props down into a component
```javascript
// in es 5
<SomeComponent someData={this.props.someData} dispatch={this.props.dispatch} />
// in es6
<SomeComponent {...this.props} />
```
3. Arrow functions: Makes compact syntax
```javascript
// es 5
var users = usersList.map(function (user) {
return <li>{user.name}</li>;
});
// es 6
const users = usersList.map((user) => <li>{user.name}</li>);
```
**[⬆ Back to Top](#table-of-contents)**
319. ### What is Concurrent Rendering?
The Concurrent rendering makes React apps to be more responsive by rendering component trees without blocking the main UI thread. It allows React to interrupt a long-running render to handle a high-priority event. i.e, When you enabled concurrent Mode, React will keep an eye on other tasks that need to be done, and if there's something with a higher priority it will pause what it is currently rendering and let the other task finish first. You can enable this in two ways,
```javascript
// 1. Part of an app by wrapping with ConcurrentMode
<React.unstable_ConcurrentMode>
<Something />
</React.unstable_ConcurrentMode>;
// 2. Whole app using createRoot
ReactDOM.unstable_createRoot(domNode).render(<App />);
```
**[⬆ Back to Top](#table-of-contents)**
320. ### What is the difference between async mode and concurrent mode?
Both refers the same thing. Previously concurrent Mode being referred to as "Async Mode" by React team. The name has been changed to highlight React’s ability to perform work on different priority levels. So it avoids the confusion from other approaches to Async Rendering.
**[⬆ Back to Top](#table-of-contents)**
321. ### Can I use javascript urls in react16.9?
Yes, you can use javascript: URLs but it will log a warning in the console. Because URLs starting with javascript: are dangerous by including unsanitized output in a tag like `<a href>` and create a security hole.
```javascript
const companyProfile = {
website: "javascript: alert('Your website is hacked')",
};
// It will log a warning
<a href={companyProfile.website}>More details</a>;
```
Remember that the future versions will throw an error for javascript URLs.
**[⬆ Back to Top](#table-of-contents)**
322. ### What is the purpose of eslint plugin for hooks?
The ESLint plugin enforces rules of Hooks to avoid bugs. It assumes that any function starting with ”use” and a capital letter right after it is a Hook. In particular, the rule enforces that,
1. Calls to Hooks are either inside a PascalCase function (assumed to be a component) or another useSomething function (assumed to be a custom Hook).
2. Hooks are called in the same order on every render.
**[⬆ Back to Top](#table-of-contents)**
323. ### What is the difference between Imperative and Declarative in React?
Imagine a simple UI component, such as a "Like" button. When you tap it, it turns blue if it was previously grey, and grey if it was previously blue.
The imperative way of doing this would be:
```javascript
if (user.likes()) {
if (hasBlue()) {
removeBlue();
addGrey();
} else {
removeGrey();
addBlue();
}
}
```
Basically, you have to check what is currently on the screen and handle all the changes necessary to redraw it with the current state, including undoing the changes from the previous state. You can imagine how complex this could be in a real-world scenario.
In contrast, the declarative approach would be:
```javascript
if (this.state.liked) {
return <blueLike />;
} else {
return <greyLike />;
}
```
Because the declarative approach separates concerns, this part of it only needs to handle how the UI should look in a sepecific state, and is therefore much simpler to understand.
**[⬆ Back to Top](#table-of-contents)**
324. ### What are the benefits of using typescript with reactjs?
Below are some of the benefits of using typescript with Reactjs,
1. It is possible to use latest JavaScript features
2. Use of interfaces for complex type definitions
3. IDEs such as VS Code was made for TypeScript
4. Avoid bugs with the ease of readability and Validation
**[⬆ Back to Top](#table-of-contents)**
325. ### How do you make sure that user remains authenticated on page refresh while using Context API State Management?
When a user logs in and reload, to persist the state generally we add the load user action in the useEffect hooks in the main App.js. While using Redux, loadUser action can be easily accessed.
**App.js**
```js
import { loadUser } from "../actions/auth";
store.dispatch(loadUser());
```
- But while using **Context API**, to access context in App.js, wrap the AuthState in index.js so that App.js can access the auth context. Now whenever the page reloads, no matter what route you are on, the user will be authenticated as **loadUser** action will be triggered on each re-render.
**index.js**
```js
import React from "react";
import ReactDOM from "react-dom";
import App from "./App";
import AuthState from "./context/auth/AuthState";
ReactDOM.render(
<React.StrictMode>
<AuthState>
<App />
</AuthState>
</React.StrictMode>,
document.getElementById("root")
);
```
**App.js**
```js
const authContext = useContext(AuthContext);
const { loadUser } = authContext;
useEffect(() => {
loadUser();
}, []);
```
**loadUser**
```js
const loadUser = async () => {
const token = sessionStorage.getItem("token");
if (!token) {
dispatch({
type: ERROR,
});
}
setAuthToken(token);
try {
const res = await axios("/api/auth");
dispatch({
type: USER_LOADED,
payload: res.data.data,
});
} catch (err) {
console.error(err);
}
};
```
**[⬆ Back to Top](#table-of-contents)**
326. ### What are the benefits of new JSX transform?
There are three major benefits of new JSX transform,
1. It is possible to use JSX without importing React packages
2. The compiled output might improve the bundle size in a small amount
3. The future improvements provides the flexibility to reduce the number of concepts to learn React.
**[⬆ Back to Top](#table-of-contents)**
327. ### How is the new JSX transform different from old transform??
The new JSX transform doesn’t require React to be in scope. i.e, You don't need to import React package for simple scenarios.
Let's take an example to look at the main differences between the old and the new transform,
**Old Transform:**
```js
import React from "react";
function App() {
return <h1>Good morning!!</h1>;
}
```
Now JSX transform convert the above code into regular JavaScript as below,
```js
import React from "react";
function App() {
return React.createElement("h1", null, "Good morning!!");
}
```
**New Transform:**
The new JSX transform doesn't require any React imports
```js
function App() {
return <h1>Good morning!!</h1>;
}
```
Under the hood JSX transform compiles to below code
```js
import { jsx as _jsx } from "react/jsx-runtime";
function App() {
return _jsx("h1", { children: "Good morning!!" });
}
```
**Note:** You still need to import React to use Hooks.
**[⬆ Back to Top](#table-of-contents)**
328. ### How do you get redux scaffolding using create-react-app?
Redux team has provided official redux+js or redux+typescript templates for create-react-app project. The generated project setup includes,
1. Redux Toolkit and React-Redux dependencies
2. Create and configure Redux store
3. React-Redux `<Provider>` passing the store to React components
4. Small "counter" example to demo how to add redux logic and React-Redux hooks API to interact with the store from components
The below commands need to be executed along with template option as below,
5. **Javascript template:**
```js
npx create-react-app my-app --template redux
```
2. **Typescript template:**
```js
npx create-react-app my-app --template redux-typescript
```
**[⬆ Back to Top](#table-of-contents)**
329. ### What are React Server components?
React Server Component is a way to write React component that gets rendered in the server-side with the purpose of improving React app performance. These components allow us to load components from the backend.
**Note:** React Server Components is still under development and not recommended for production yet.
**[⬆ Back to Top](#table-of-contents)**
330. ### What is prop drilling?
Prop Drilling is the process by which you pass data from one component of the React Component tree to another by going through other components that do not need the data but only help in passing it around.
**[⬆ Back to Top](#table-of-contents)**
331. ### What is state mutation and how to prevent it?
`State mutation` happens when you try to update the state of a component without actually using `setState` function. This can happen when you are trying to do some computations using a state variable and unknowingly save the result in the same state variable. This is the main reason why it is advised to return new instances of state variables from the reducers by using Object.assign({}, ...) or spread syntax.
This can cause unknown issues in the UI as the value of the state variable got updated without telling React to check what all components were being affected from this update and it can cause UI bugs.
Ex:
```javascript
class A extends React.component {
constructor(props) {
super(props);
this.state = {
loading: false
}
}
componentDidMount() {
let { loading } = this.state;
loading = (() => true)(); // Trying to perform an operation and directly saving in a state variable
}
```
**How to prevent it:** Make sure your state variables are immutable by either enforcing immutability by using plugins like Immutable.js, always using `setState` to make updates, and returning new instances in reducers when sending updated state values.
**[⬆ Back to Top](#table-of-contents)**
332. ### What is the difference between useState and useRef hook?
1. useState causes components to re-render after state updates whereas useRef doesn’t cause a component to re-render when the value or state changes.
Essentially, useRef is like a “box” that can hold a mutable value in its (.current) property.
2. useState allows us to update the state inside components. While useRef allows referencing DOM elements.
**[⬆ Back to Top](#table-of-contents)**
333. ### What is a wrapper component?
A wrapper in React is a component that wraps or surrounds another component or group of components. It can be used for a variety of purposes such as adding additional functionality, styling, or layout to the wrapped components.
For example, consider a simple component that displays a message:
```javascript
const Message = ({ text }) => {
return <p>{text}</p>;
};
```
We can create a wrapper component that will add a border to the message component:
```javascript
const MessageWrapper = (props) => {
return (
<div style={{ border: "1px solid black" }}>
<Message {...props} />
</div>
);
};
```
Now we can use the MessageWrapper component instead of the Message component and the message will be displayed with a border:
```javascript
<MessageWrapper text="Hello World" />
```
Wrapper component can also accept its own props and pass them down to the wrapped component, for example, we can create a wrapper component that will add a title to the message component:
```javascript
const MessageWrapperWithTitle = ({title, ...props}) => {
return (
<div>
<h3>{title}</h3>
<Message {...props} />
</div>
);
};
```
Now we can use the MessageWrapperWithTitle component and pass title props:
```javascript
<MessageWrapperWithTitle title="My Message" text="Hello World" />
```
This way, the wrapper component can add additional functionality, styling, or layout to the wrapped component while keeping the wrapped component simple and reusable.
**[⬆ Back to Top](#table-of-contents)**
334. ### What are the differences between useEffect and useLayoutEffect hooks?
useEffect and useLayoutEffect are both React hooks that can be used to synchronize a component with an external system, such as a browser API or a third-party library. However, there are some key differences between the two:
- Timing: useEffect runs after the browser has finished painting, while useLayoutEffect runs synchronously before the browser paints. This means that useLayoutEffect can be used to measure and update layout in a way that feels more synchronous to the user.
- Browser Paint: useEffect allows browser to paint the changes before running the effect, hence it may cause some visual flicker. useLayoutEffect synchronously runs the effect before browser paints and hence it will avoid visual flicker.
- Execution Order: The order in which multiple useEffect hooks are executed is determined by React and may not be predictable. However, the order in which multiple useLayoutEffect hooks are executed is determined by the order in which they were called.
- Error handling: useEffect has a built-in mechanism for handling errors that occur during the execution of the effect, so that it does not crash the entire application. useLayoutEffect does not have this mechanism, and errors that occur during the execution of the effect will crash the entire application.
In general, it's recommended to use useEffect as much as possible, because it is more performant and less prone to errors. useLayoutEffect should only be used when you need to measure or update layout, and you can't achieve the same result using useEffect.
**[⬆ Back to Top](#table-of-contents)**
335. ### What are the differences between Functional and Class Components?
There are two different ways to create components in ReactJS. The main differences are listed down as below,
## 1. Syntax:
The classs components uses ES6 classes to create the components. It uses `render` function to display the HTML content in the webpage.
The syntax for class component looks like as below.
```js
class App extends Reacts.Component {
render(){
return <h1>This is a class component</h1>}
}
```
**Note:** The **Pascal Case** is the recommended approach to provide naming to a component.
Functional component has been improved over the years with some added features like Hooks. Here is a syntax for functional component.
```js
function App(){
return <div className="App">
<h1>Hello, I'm a function component</h1>
</div>
}
```
## 2. State:
State contains information or data about a component which may change over time.
In class component, you can update the state when a user interacts with it or server updates the data using the `setState()` method. The initial state is going to be assigned in the `Constructor( ) `method using the the ` this.state` object and it is possible to different data types in the `this.state` object such as string, boolean, numbers, etc.
**A simple example showing how we use the setState() and constructor()**
```js
class App extends Component {
constructor() {
super();
this.state = {
message: "This is a class component",
};
}
updateMessage() {
this.setState({t
message: "Updating the class component",
});
}
render() {
return (
<>
<h1>{this.state.message}</h1>
<button
onClick={() => {
this.updateMessage();
}}>
Click!!
</button>
</>
);
}
}
```
You not use state in functional components because it was only supported in class components. But over the years hooks have been implemented in functional component which enable to use state in functional component too.
The `useState()` hook can used to implement state in funcitonal component. It returns an array with two items: the first item is current state and the next one is a function (setState) that updates the value of the current state.
Let's see an example to demonstrate the state in functional components,
```js
function App() {
const [message, setMessage] = useState("This is a functional component");
const updateMessage = () => {
setMessage("Updating the functional component");
};
return (
<div className="App">
<h1>{message} </h1>
<button onClick={updateMessage}>Click me!!</button>
</div>
);
}
```
## 4. Props:
Props are referred to as "properties". The props are passed into react component just like arguments passed to a function. In otherwords, they are similar to HTML attributes.
The props are accessible in child class component using `this.props` as shown in below example,
```js
class Child extends React.Component {
render() {
return <h1> This is a functional component and component name is {this.props.name} </h1>;
}
}
class Parent extends React.Component {
render() {
return (
<div className="Parent">
<Child name="First child component" />
<Child name="Second child component" />
</div>
);
}
}
```
Props in functional components are similar to that of the class components but the difference is the absence of 'this' keyword.
```js
function Child(props) {
return <h1>This is a child component and the component name is{props.name}</h1>;
}
function Parent() {
return (
<div className="Parent">
<Child name="First child component" />
<Child name="Second child component" />
</div>
);
}
```
**[⬆ Back to Top](#table-of-contents)**
336. ### What is strict mode in React?
`React.StrictMode` is a useful component for highlighting potential problems in an application. Just like `<Fragment>`, `<StrictMode>` does not render any extra DOM elements. It activates additional checks and warnings for its descendants. These checks apply for _development mode_ only.
```jsx harmony
import React from "react";
function ExampleApplication() {
return (
<div>
<Header />
<React.StrictMode>
<div>
<ComponentOne />
<ComponentTwo />
</div>
</React.StrictMode>
<Header />
</div>
);
}
```
In the example above, the _strict mode_ checks apply to `<ComponentOne>` and `<ComponentTwo>` components only. i.e., Part of the application only.
**[⬆ Back to Top](#table-of-contents)**
337. ### What is the benefit of strict mode?
The <StrictMode> will be helpful in the below cases,
1. Whenever the component
1. Identifying components with **unsafe lifecycle methods**.
2. Warning about **legacy string ref** API usage.
3. Detecting unexpected **side effects**.
4. Detecting **legacy context** API.
5. Warning about deprecated findDOMNode usage
**[⬆ Back to Top](#table-of-contents)**
336. ### Why does strict mode render twice in React?
StrictMode renders components twice in development mode(not production) in order to detect any problems with your code and warn you about those problems. This is used to detect accidental side effects in the render phase. If you used `create-react-app` development tool then it automatically enables StrictMode by default.
```js
ReactDOM.render(
<React.StrictMode>
{App}
</React.StrictMode>,
document.getElementById('root')
);
```
If you want to disable this behavior then you can remove `strict` mode.
```js
ReactDOM.render(
{App},
document.getElementById('root')
);
```
To detect side effects the following functions are invoked twice:
1. Class component constructor, render, and shouldComponentUpdate methods
2. Class component static getDerivedStateFromProps method
3. Function component bodies
4. State updater functions
5. Functions passed to useState, useMemo, or useReducer (any Hook)
**[⬆ Back to Top](#table-of-contents)**
## Disclaimer
The questions provided in this repository are the summary of frequently asked questions across numerous companies. We cannot guarantee that these questions will actually be asked during your interview process, nor should you focus on memorizing all of them. The primary purpose is for you to get a sense of what some companies might ask — do not get discouraged if you don't know the answer to all of them — that is ok!
Good luck with your interview 😊
---
| List of top 500 ReactJS Interview Questions & Answers....Coding exercise questions are coming soon!! | interview,interview-practice,interview-preparation,interview-questions,interview-questions-javascript,javascript,javascript-interview-questions,react,react-router,redux | 2024-03-29T08:11:50Z | 2024-03-29T08:11:06Z | null | 1 | 0 | 1 | 0 | 0 | 4 | null | null | JavaScript |
stefan2do/freeCodeCamp | main | [](https://www.freecodecamp.org/)
## freeCodeCamp.org's open-source codebase and curriculum
[freeCodeCamp.org](https://www.freecodecamp.org) is a friendly community where you can learn to code for free. It is run by a [donor-supported 501(c)(3) charity](https://www.freecodecamp.org/donate) to help millions of busy adults transition into tech. Our community has already helped more than 40,000 people get their first developer job.
Our full-stack web development and machine learning curriculum is completely free and self-paced. We have thousands of interactive coding challenges to help you expand your skills.
### Certifications
freeCodeCamp.org offers several free developer certifications. Each of these certifications involves building 5 required web app projects, along with hundreds of optional coding challenges to help you prepare for those projects. We estimate that each certification will take a beginner programmer around 300 hours to earn.
Each of these 50 projects in the freeCodeCamp.org curriculum has its own agile user stories and automated tests. These help you build up your project incrementally and ensure you've fulfilled all the user stories before you submit it.
You can pull in these test suites through [freeCodeCamp's CDN](https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js). This means you can build these projects on websites like CodePen and Replit - or even on your local computer's development environment.
Once you've earned a certification, you will always have it. You will always be able to link to it from your LinkedIn or resume. And when your prospective employers or freelance clients click that link, they'll see a verified certification specific to you.
The one exception to this is if we discover violations of our [Academic Honesty Policy](https://www.freecodecamp.org/news/academic-honesty-policy/). When we catch people unambiguously plagiarizing (submitting other people's code or projects as their own without citation), we do what all rigorous institutions of learning should do - we revoke their certifications and ban those people.
Here are our ten core certifications:
#### 1. [Responsive Web Design Certification](https://www.freecodecamp.org/learn/2022/responsive-web-design/)
- [Learn HTML by Building a Cat Photo App](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-html-by-building-a-cat-photo-app)
- [Learn Basic CSS by Building a Cafe Menu](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-basic-css-by-building-a-cafe-menu)
- [Learn CSS Colors by Building a Set of Colored Markers](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-colors-by-building-a-set-of-colored-markers)
- [Learn HTML Forms by Building a Registration Form](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-html-forms-by-building-a-registration-form)
- [Learn the CSS Box Model by Building a Rothko Painting](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-the-css-box-model-by-building-a-rothko-painting)
- [Learn CSS Flexbox by Building a Photo Gallery](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-flexbox-by-building-a-photo-gallery)
- [Learn Typography by Building a Nutrition Label](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-typography-by-building-a-nutrition-label)
- [Learn Accessibility by Building a Quiz](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-accessibility-by-building-a-quiz)
- [Learn More About CSS Pseudo Selectors By Building A Balance Sheet](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-more-about-css-pseudo-selectors-by-building-a-balance-sheet)
- [Learn Intermediate CSS by Building a Picasso Painting](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-intermediate-css-by-building-a-picasso-painting)
- [Learn Responsive Web Design by Building a Piano](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-responsive-web-design-by-building-a-piano)
- [Learn CSS Variables by Building a City Skyline](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-variables-by-building-a-city-skyline)
- [Learn CSS Grid by Building a Magazine](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-grid-by-building-a-magazine)
- [Learn CSS Transforms by Building a Penguin](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-transforms-by-building-a-penguin)
- [Learn CSS Animations by Building a Ferris Wheel](https://www.freecodecamp.org/learn/2022/responsive-web-design/#learn-css-animation-by-building-a-ferris-wheel)
<br />
<br />
**Projects**: [Survey Form](https://www.freecodecamp.org/learn/2022/responsive-web-design/build-a-survey-form-project/build-a-survey-form), [Tribute Page](https://www.freecodecamp.org/learn/2022/responsive-web-design/build-a-tribute-page-project/build-a-tribute-page), [Technical Documentation Page](https://www.freecodecamp.org/learn/2022/responsive-web-design/build-a-technical-documentation-page-project/build-a-technical-documentation-page), [Product Landing Page](https://www.freecodecamp.org/learn/2022/responsive-web-design/build-a-product-landing-page-project/build-a-product-landing-page), [Personal Portfolio Webpage](https://www.freecodecamp.org/learn/2022/responsive-web-design/build-a-personal-portfolio-webpage-project/build-a-personal-portfolio-webpage)
#### 2. [JavaScript Algorithms and Data Structures Certification](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/)
- [Basic JavaScript](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#basic-javascript)
- [ES6](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#es6)
- [Regular Expressions](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#regular-expressions)
- [Debugging](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#debugging)
- [Basic Data Structures](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#basic-data-structures)
- [Basic Algorithm Scripting](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#basic-algorithm-scripting)
- [Object-Oriented Programming](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#object-oriented-programming)
- [Functional Programming](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#functional-programming)
- [Intermediate Algorithm Scripting](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/#intermediate-algorithm-scripting)
<br />
<br />
**Projects**: [Palindrome Checker](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/palindrome-checker),[ Roman Numeral Converter](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/roman-numeral-converter), [Caesar's Cipher](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/caesars-cipher), [Telephone Number Validator](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/telephone-number-validator), [Cash Register](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/cash-register)
#### 3. [Front End Libraries Certification](https://www.freecodecamp.org/learn/front-end-development-libraries/)
- [Bootstrap](https://www.freecodecamp.org/learn/front-end-development-libraries/#bootstrap)
- [jQuery](https://www.freecodecamp.org/learn/front-end-development-libraries/#jquery)
- [Sass](https://www.freecodecamp.org/learn/front-end-development-libraries/#sass)
- [React](https://www.freecodecamp.org/learn/front-end-development-libraries/#react)
- [Redux](https://www.freecodecamp.org/learn/front-end-development-libraries/#redux)
- [React and Redux](https://www.freecodecamp.org/learn/front-end-development-libraries/#react-and-redux)
<br />
<br />
**Projects**: [Random Quote Machine](https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-random-quote-machine), [Markdown Previewer](https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-markdown-previewer), [Drum Machine](https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-drum-machine), [JavaScript Calculator](https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-javascript-calculator), [25 + 5 Clock](https://www.freecodecamp.org/learn/front-end-development-libraries/front-end-development-libraries-projects/build-a-25--5-clock)
#### 4. [Data Visualization Certification](https://www.freecodecamp.org/learn/data-visualization/)
- [Data Visualization with D3](https://www.freecodecamp.org/learn/data-visualization/#data-visualization-with-d3)
- [JSON APIs and Ajax](https://www.freecodecamp.org/learn/data-visualization/#json-apis-and-ajax)
<br />
<br />
**Projects**: [Bar Chart](https://www.freecodecamp.org/learn/data-visualization/data-visualization-projects/visualize-data-with-a-bar-chart), [Scatterplot Graph](https://www.freecodecamp.org/learn/data-visualization/data-visualization-projects/visualize-data-with-a-scatterplot-graph), [Heat Map](https://www.freecodecamp.org/learn/data-visualization/data-visualization-projects/visualize-data-with-a-heat-map), [Choropleth Map](https://www.freecodecamp.org/learn/data-visualization/data-visualization-projects/visualize-data-with-a-choropleth-map), [Treemap Diagram](https://www.freecodecamp.org/learn/data-visualization/data-visualization-projects/visualize-data-with-a-treemap-diagram)
#### 5. [APIs and Microservices Certification](https://www.freecodecamp.org/learn/back-end-development-and-apis/)
- [Managing Packages with Npm](https://www.freecodecamp.org/learn/back-end-development-and-apis/#managing-packages-with-npm)
- [Basic Node and Express](https://www.freecodecamp.org/learn/back-end-development-and-apis/#basic-node-and-express)
- [MongoDB and Mongoose](https://www.freecodecamp.org/learn/back-end-development-and-apis/#mongodb-and-mongoose)
<br />
<br />
**Projects**: [Timestamp Microservice](https://www.freecodecamp.org/learn/back-end-development-and-apis/back-end-development-and-apis-projects/timestamp-microservice), [Request Header Parser](https://www.freecodecamp.org/learn/back-end-development-and-apis/back-end-development-and-apis-projects/request-header-parser-microservice), [URL Shortener](https://www.freecodecamp.org/learn/back-end-development-and-apis/back-end-development-and-apis-projects/url-shortener-microservice), [Exercise Tracker](https://www.freecodecamp.org/learn/back-end-development-and-apis/back-end-development-and-apis-projects/exercise-tracker), [File Metadata Microservice](https://www.freecodecamp.org/learn/back-end-development-and-apis/back-end-development-and-apis-projects/file-metadata-microservice)
#### 6. [Quality Assurance Certification](https://www.freecodecamp.org/learn/quality-assurance/)
- [Quality Assurance and Testing with Chai](https://www.freecodecamp.org/learn/quality-assurance/#quality-assurance-and-testing-with-chai)
- [Advanced Node and Express](https://www.freecodecamp.org/learn/quality-assurance/#advanced-node-and-express)
<br />
<br />
**Projects**: [Metric-Imperial Converter](https://www.freecodecamp.org/learn/quality-assurance/quality-assurance-projects/metric-imperial-converter), [Issue Tracker](https://www.freecodecamp.org/learn/quality-assurance/quality-assurance-projects/issue-tracker), [Personal Library](https://www.freecodecamp.org/learn/quality-assurance/quality-assurance-projects/personal-library), [Sudoku Solver](https://www.freecodecamp.org/learn/quality-assurance/quality-assurance-projects/sudoku-solver), [American British Translator](https://www.freecodecamp.org/learn/quality-assurance/quality-assurance-projects/american-british-translator)
#### 7. [Scientific Computing with Python Certification](https://www.freecodecamp.org/learn/scientific-computing-with-python/)
- [Introduction to Python for Everybody](https://www.freecodecamp.org/learn/scientific-computing-with-python/#python-for-everybody)
<br />
<br />
**Projects**: [Arithmetic Formatter](https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/arithmetic-formatter), [Time Calculator](https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/time-calculator), [Budget App](https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/budget-app), [Polygon Area Calculator](https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/polygon-area-calculator), [Probability Calculator](https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/probability-calculator)
#### 8. [Data Analysis with Python Certification](https://www.freecodecamp.org/learn/data-analysis-with-python/)
- [Data Analysis with Python Course](https://www.freecodecamp.org/learn/data-analysis-with-python/#data-analysis-with-python-course)
- [NumPy](https://www.freecodecamp.org/learn/data-analysis-with-python/#numpy)
<br />
<br />
**Projects**: [Mean-Variance-Standard Deviation Calculator](https://www.freecodecamp.org/learn/data-analysis-with-python/data-analysis-with-python-projects/mean-variance-standard-deviation-calculator), [Demographic Data Analyzer](https://www.freecodecamp.org/learn/data-analysis-with-python/data-analysis-with-python-projects/demographic-data-analyzer), [Medical Data Visualizer](https://www.freecodecamp.org/learn/data-analysis-with-python/data-analysis-with-python-projects/medical-data-visualizer), [Page View Time Series Visualizer](https://www.freecodecamp.org/learn/data-analysis-with-python/data-analysis-with-python-projects/page-view-time-series-visualizer), [Sea Level Predictor](https://www.freecodecamp.org/learn/data-analysis-with-python/data-analysis-with-python-projects/sea-level-predictor)
#### 9. [Information Security Certification](https://www.freecodecamp.org/learn/information-security/)
- [Information Security with HelmetJS](https://www.freecodecamp.org/learn/information-security/#information-security-with-helmetjs)
- [Python for Penetration Testing](https://www.freecodecamp.org/learn/information-security/#python-for-penetration-testing)
<br />
<br />
**Projects**: [Stock Price Checker](https://www.freecodecamp.org/learn/information-security/information-security-projects/stock-price-checker), [Anonymous Message Board](https://www.freecodecamp.org/learn/information-security/information-security-projects/anonymous-message-board), [Port Scanner](https://www.freecodecamp.org/learn/information-security/information-security-projects/port-scanner), [SHA-1 Password Cracker](https://www.freecodecamp.org/learn/information-security/information-security-projects/sha-1-password-cracker), [Secure Real Time Multiplayer Game ](https://www.freecodecamp.org/learn/information-security/information-security-projects/secure-real-time-multiplayer-game)
#### 10. [Machine Learning with Python Certification](https://www.freecodecamp.org/learn/machine-learning-with-python/)
- [TensorFlow](https://www.freecodecamp.org/learn/machine-learning-with-python/#tensorflow)
- [How Neural Networks Work](https://www.freecodecamp.org/learn/machine-learning-with-python/#how-neural-networks-work)
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<br />
**Projects**: [Rock Paper Scissors](https://www.freecodecamp.org/learn/machine-learning-with-python/machine-learning-with-python-projects/rock-paper-scissors), [Cat and Dog Image Classifier](https://www.freecodecamp.org/learn/machine-learning-with-python/machine-learning-with-python-projects/cat-and-dog-image-classifier), [Book Recommendation Engine using KNN](https://www.freecodecamp.org/learn/machine-learning-with-python/machine-learning-with-python-projects/book-recommendation-engine-using-knn), [Linear Regression Health Costs Calculator](https://www.freecodecamp.org/learn/machine-learning-with-python/machine-learning-with-python-projects/linear-regression-health-costs-calculator), [Neural Network SMS Text Classifier](https://www.freecodecamp.org/learn/machine-learning-with-python/machine-learning-with-python-projects/neural-network-sms-text-classifier)
#### Legacy Full Stack Development Certification
Once you have earned the Responsive Web Design, Algorithms and Data Structures, Front End Development Libraries, Data Visualization, Back End Development and APIs, and Legacy Information Security and Quality Assurance certifications, you'll be able to claim your freeCodeCamp.org Full Stack Development Certification. This distinction signifies that you've completed around 1,800 hours of coding with a wide range of web development tools.
#### Legacy Certifications
We also have 4 legacy certifications dating back to our 2015 curriculum, which are still available. All of the required projects for these legacy certifications will remain available on freeCodeCamp.org.
- Legacy Front End Development Certification
- Legacy Data Visualization Certification
- Legacy Back End Development Certification
- Legacy Information Security and Quality Assurance Certification
| My freeCodeCamp solutions | css,freecodecamp,html,javascript,reactjs | 2024-04-19T18:08:50Z | 2024-04-19T18:15:19Z | null | 1 | 0 | 1 | 0 | 1 | 4 | null | null | JavaScript |
boywithkeyboard/warp | main | null | Setup Cloudflare WARP in GitHub Actions (for IPv6 support). 💫 | cloudflare,cloudflare-warp,github,github-actions,javascript,node,nodejs,proxy,warp,ipv6 | 2024-03-24T20:52:10Z | 2024-05-07T10:04:10Z | 2024-03-25T21:14:04Z | 1 | 11 | 26 | 0 | 2 | 4 | null | Apache-2.0 | JavaScript |
7xmohamed/AuraFashion | main | # AuraFashion
| AuraFashion is a website for an e-commerce store | ecommerce,fashion,bootstrap,clothing,css,html,javascript | 2024-03-19T11:19:53Z | 2024-05-05T00:15:42Z | null | 4 | 1 | 50 | 0 | 0 | 4 | null | null | HTML |
tenoxui/cli | main | # TenoxUI CLI
## Installation
```sh
npm i -g @tenoxui/cli
```
Usage :
```sh
tenoxui [option]
```
## Initialization
```sh
tenoxui init
```
it will generate a tenoxui configuration file.
## Configuration
`tenoxui.config.cjs` :
```js
module.exports = {
inputFiles: "./**/*.html",
inputStyles: {
".m-1": "m-2px",
".m-3": "m-6px",
".btn": "bdr-none br-4px bg-red pv-2px ph-8px",
},
outputStyles: "dist/output.js",
};
```
## Run
Build :
```sh
tenoxui
```
Watch mode :
```sh
tenoxui -w
```
```sh
tenoxui --watch
```
| null | cli-tools,web-development,frontend-tools,cli,react,html,css,js,ts,javascript | 2024-04-19T08:18:23Z | 2024-04-22T11:21:03Z | 2024-04-21T16:00:45Z | 2 | 4 | 20 | 0 | 1 | 4 | null | MIT | JavaScript |
morganm94/Food-Identifier | main | # Know-Before-You-Eat
An Interactive web application for identifying food names based on the images, providing nutritional facts (For eg: calculating calories of the food you're eating) for diet advice and predicting the recipes based on the predicted food names.
## <ins> Final Deployed Application Link </ins>
## <ins> Presentation Link </ins>
https://drive.google.com/file/d/1RufkM7jekyF-5DaBEeNuWt1R1k_Tdox1/view?usp=sharing
## <ins> Source Data </ins>
1) Food101 Dataset
https://www.vision.ee.ethz.ch/datasets_extra/food-101/
2) Nutritional Facts
https://www.fatsecret.com/calories-nutrition/
http://ahealthylifeforme.com
3) Recipe
https://www.kaggle.com/kaggle/recipie-ingredients-dataset
https://en.wikipedia.org/wiki/
## <ins> Tools/Models Reference </ins>
1) Classification/Training Models
> Transfer Learning With MobileNet
> Transfer Learning With VGG16
> KNN & Random Forest
2) Keras Image Data Generator for Image Augmentation
3) Front End Application - HTML, CSS, Bootstrap and Javascript
4) Retrieving Data From Back End : Python (SQLAlchemy and Flask)
5) Missing Link AI - Platform to Run deep learning experiments on hundreds of machines, on and off the cloud, manage huge data sets and gain unprecedented visibility into your experiments.
https://missinglink.ai/
Presentation: https://docs.google.com/presentation/d/1UvU7sMPkn2Y5I88bmdoH0Sog3SpyQeSPeVdtSZoHrDk/edit#slide=id.g6ea730b6b1_7_5
## <ins> Results </ins>
1) After fine-tuning a pre-trained MobileNet model achieved about 99.03% Top-1 Accuracy on the Training set and about 73% accuracy on Valid & test data.
2) After fine-tuning a pre-trained VGG16 model achieved about 98.03% Top-1 Accuracy on the Training set and about 70% accuracy on Valid & test data.
3) Using KNN Algorithm achieved at score:0.404 at K=3
4) Using Random Forest Model achieved at score:0.2
## <ins> Key TakeAways </ins>
1) Through application of Various Machine Learning Algorithms - K-Nearest Neighbors, Random Forest Classification and Deep Learning(CNN) Algorithms for image classification we concluded that CNN is the best model for classification of images in our data set.
2) In CNN pretrained models Mobilenet model is the best in terms of both speed and accuracy in our dataset.
3) MobileNet is the best method and quickest way to implement transfer learning for CNN’s.
| An Interactive web application for identifying food names based on the images, providing nutritional facts. | css,html,javascript,knn,mobilenet,python,random-forest,vgg16 | 2024-03-17T21:06:29Z | 2024-03-26T04:47:41Z | null | 1 | 0 | 38 | 0 | 1 | 4 | null | null | Jupyter Notebook |
coding-aqyanoos/login-registration-react-js-web-api-asp-net-core-identity-authentication | main | # Login and Registration with .NET 8 Identity.
In this project you will learn how to implement Authentication and Authorization in ASP .NET Core Web API with REACT.JS for the Frontend. This is an advance topic in web development.
### What will you learn?
You will learn the following:
- Creating a user interface using React.JS.
- Creating protected routes in REACT.JS.
- Creating RestFull API using ASP .NET Core Web API (.NET 8 LTS).
- Handling API requests using JavaScript fetch API.
- Cookie based Authentication.
- Entity Framework and SQL Database.
- HTML and CSS.
- JavaScript.
- C#
Watch the full course on YouTube [here](https://youtu.be/DK7YAqd0tJA). Visit our YouTube Channel [Coding Aqyanoos](https://www.youtube.com/@coding-aqyanoos) for more useful and helpful courses. If you have any other questions please our website [https://aqyanoos.com](https://aqyanoos.com).
We Have also created unique helpful Android apps that you can install and use for free. For more details visit our website.
__Thank You__
| Login and Registration - Authentication and Authorization in ASP .NET 8 Core Web API and React.js. | asp-net-core-identity,asp-net-core-web-api,css,entity-framework-core,full-course,html,javascript,learn-react,learn-reactjs,login | 2024-03-24T10:53:10Z | 2024-03-24T11:30:02Z | null | 1 | 0 | 3 | 0 | 0 | 4 | null | MIT | C# |
najmiter/timid | main | # timid
A timetable maker with looks easy on the eyes and a friendly app to keep track of the current lecture, hopefully.
## Logs
- March 28, 2024
- **Make a printable timetable** that is stored locally as well (data won't be destroyed between reloads/restarts).
- **Add a title** of the table that will only appear on the print.
- **Clear** the data of the entire table.
- March 29, 2024
- **See all the lectures** on the current day on the `<Current />` with friendly styling.
- **Share a link** after making the timetable with anyone on the internet. If they open the link, they will be shown the `<Current />` according to the params in the URL that you shared. If they open on the phone for the first time using the URL with the timetable data, that data will be stored locally in their device and next time they may even just open the root of the app (on phone) and they will be shown the `<Current />`.
| a good looking timetable maker and a friendly app to keep track of the current lecture, hopefully | css,html,javascript,js,react,reactjs,web,webdevelopment | 2024-03-25T10:27:21Z | 2024-03-31T19:34:40Z | null | 1 | 0 | 75 | 0 | 0 | 4 | null | null | JavaScript |
gabriel-logan/Auto | main | # Auto
This repository contains several scripts that automate common software development tasks.
Any programming language is welcome, as long as it is possible to run the script in a Linux, Windows or Mac environment.
I count on everyone's collaboration to add useful scripts that can be reused by other developers.
Follow the instructions in the CONTRIBUTING.md file to add a new script.
### External libraries are also welcome
## How to use
See the documentation for each module to learn how to use it.
## Documentation
- [Gitpush](https://github.com/gabriel-logan/Auto/blob/main/src/packages/c/gitpush/README.md) - Automate the process of adding, committing and pushing changes to a git repository.
## Available modules - SOURCES
- [Gitpush](https://github.com/gabriel-logan/Auto/tree/main/src/packages/c/gitpush/gitpush.c) - Source code for the Gitpush module.
## Available modules - EXECUTABLE
- Gitpush
### Download links below
#### Windows
- [Gitpush](https://github.com/gabriel-logan/Auto/raw/main/bin/gitpush/gitpush.exe) - Executable file
#### Linux
- [Gitpush](https://github.com/gabriel-logan/Auto/raw/main/bin/gitpush/gitpush) - Executable file
## External libraries
- Clean Memory
- Easy Templates
- Node Clear Npx Cache
## Documentation
- [Clean Memory](https://github.com/gabriel-logan/clean-memory) - Shell script command to clear unused temporary memory and system cache. Clean RAM memory.
- [Easy Templates](https://github.com/gabriel-logan/easy-templates) - Library that simplifies the process of creating various templates using NPX.
- [Node Clear Npx Cache](https://github.com/return-0x0/node-clear-npx-cache) - Script command to clear the NPM cache.
## Sources
- [Clean Memory](https://github.com/gabriel-logan/clean-memory/blob/main/usr/bin/clean_memory.sh) - Source code for the Clean Memory module.
- [Easy Templates](https://github.com/gabriel-logan/easy-templates/tree/main/src) - Source code for the Easy Templates module.
- [Node Clear Npx Cache](https://github.com/return-0x0/node-clear-npx-cache/blob/master/src/index.ts) - Source code for the Node Clear Npx Cache module.
## Executable
### Command line
- Easy Templates
```bash
npx easy-templates
```
- Node Clear Npx Cache
```bash
npx clear-npx-cache
```
### Download links below
#### Linux
- [Clean Memory](https://github.com/gabriel-logan/clean-memory/raw/main/package/clean-memory.deb) - Executable file | Repository with several codes that automate tasks in a practical way. | automation,c,c-plus-plus,csharp,java,javascript,linux,programming,python,typescript | 2024-04-21T04:57:01Z | 2024-04-23T10:58:01Z | null | 1 | 0 | 19 | 1 | 0 | 4 | null | MIT | C |
rickystar04/PicPortal | main | <h1 align="center"> PicPortal </h1> <br>
<p align="center"><img src="https://imgur.com/GckAf4b.png" width="50%" align="center"></p>
<p align="center">
<a href="https://www.codefactor.io/repository/github/rickystar04/picportal"><img src="https://www.codefactor.io/repository/github/rickystar04/picportal/badge" alt="CodeFactor" /></a></p>
<p>
PicPortal is an innovative Chrome extension designed to enhance your daily internet browsing experience by transforming the standard new tab page into a vibrant display of stunning images and photographs. With PicPortal, every new tab you open becomes a gateway to visual inspiration and creativity.</p>
## Features
- **Dynamic Image Display**: Each new tab greets you with a beautiful, high-resolution image from a curated collection, providing a refreshing start to your browsing sessions.
- **Seamless Integration**: The extension is designed to blend smoothly with your Chrome browser, ensuring a seamless and intuitive user experience.
- **Custom API Integration** The images are sourced from <a href="unsplash.com">Unsplash</a>, a platform for free-to-use, high-quality images. These images are delivered through a custom API hosted on <a href="render.com">Render</a>, ensuring that you receive a fresh and diverse selection of visuals each time you open a new tab.
- **Personalized Categories** PicPortal allows you to personalize your experience further by selecting categories of images that resonate with you. Choose from a variety of categories such as Nature, Architecture, Beaches, and more to tailor the visual inspiration on your new tab page to your preferences.
- **Favorites Synchronization**: Keep your favorite images in sync across all your devices, ensuring your personal collection of inspiration is always at hand, no matter where you are or which device you're using.
## Screenshots
<p align="center">
<img src="https://imgur.com/FkjZ0ER.png" width="100%">
</br>
</br>
<img src="https://imgur.com/Wijlvah.png" width="100%">
</p>
## Installation
1. Clone the repository locally:
```console
git clone https://github.com/rickystar04/PicPortal.git
```
2. Navigate to the cloned directory via command prompt or terminal:
```console
> cd PicPortal
```
3. Install the necessary packages:
```console
> npm install
```
4. Build the project:
```console
> npm run build
```
5. Open Chrome and navigate to `chrome://extensions/`.
6. Enable Developer Mode in the top right corner.
7. Click on "Load unpacked extension" and select the `build` folder inside the cloned project directory.
## Usage
After installation, whenever you open a new tab in Chrome, PicPortal's customized new tab page will be displayed.
## Upcoming Features
- :white_check_mark:**Favorites Synchronization**: ~~In addition to adding images to your favorites for quick access, we are planning to implement synchronization of your favorites across multiple devices. This will allow you to access your curated collection of inspiring images no matter where you are or which device you're using.~~
- **Bookmarks**: We are also working on a feature that will allow you to bookmark your favorite web pages directly from the new tab page. This will enable you to quickly navigate to your most visited sites and keep your favorite online content easily accessible.
## Contributing
If you would like to contribute to the project, please submit a pull request or open an issue to discuss what you would like to change.
**Note for Developers:**
The codebase uses the `chrome.storage.sync` API for saving data locally in Chrome. When running the project node with `npm start`, you will encounter an error due to the use of this API. Here's the recommended approach:
- If you want to modify parts of the code that do not involve the `chrome.storage.sync` API, consider commenting out all parts of the program where it is used. This will allow you to run the project without encountering the error related to the chrome.storage API.
- If your changes are related to the `chrome.storage.sync` API, you should rebuild the project's build file each time you want to see the changes applied by running `npm run build`. Then, reload the build in the Chrome extensions page to verify the functionality.
Please ensure that you test your changes thoroughly before submitting a pull request.
## License
This project is released under the MIT License. For more details, see the LICENSE file in the repository.
## Support
For support, you can open an issue in the GitHub repository or contact the maintainer at the email address provided in the GitHub profile.
| null | chrome-extension,chrome-extensions,javascript,newtabpage,react,reactjs | 2024-03-28T18:02:17Z | 2024-05-01T15:06:06Z | null | 1 | 1 | 24 | 0 | 0 | 4 | null | MIT | JavaScript |
Phantom-fs/Herbify | main | # HERBIFY (Herb Identification Website)
## Overview
Herbs have been utilized for centuries for their medicinal properties and culinary uses. Our website aims to help users identify over 90 types of common herbs found worldwide. By simply uploading a photo of the herb you wish to identify, our deep learning model will accurately classify the herb, providing you with the top 5 predictions made by the model.
## Features
- **Herb Identification**: Upload a photo of a herb to identify it from over 90 common types.
- **Leaf Extracted Picture**: View the processed leaf-extracted image, with white background.
- **Top 5 Predictions**: View the top 5 predictions made by our CNN model.
- **User-Friendly Interface**: Easy-to-use interface designed for seamless navigation.
- **Security**: Multiple exception cases are covered.
## Technologies Used
- **Frontend**: HTML, CSS, JavaScript
- **Backend**: Python based server
- **Model**: Transfer Learning applied PyTorch Pretrained CNN Model
- **Application Server**: Deployed on Heroku (web server + model API)
## How It Works
1. **Upload Photo**: Navigate to the website and upload a clear photo of the herb you want to identify.
2. **Processed Image**: A series of meticulous preprocessing steps is applied to the uploaded image, and the processed image is displayed.
3. **Prediction**: Our deep learning model will process the image and provide the top 5 predictions for the herb's identity.
4. **View Results**: Browse through the predictions to identify the herb accurately.
## Team
- ***[Farhan Sheth](https://www.linkedin.com/in/farhan-sheth/)***
- ***[Manvendra Jasra](https://www.linkedin.com/in/manvendra-jasra/)***
- ***[Ishika Chatter](https://www.linkedin.com/in/ishika-chatter/)***
### The code for the deployed Application server on heroku is available on the [Herbify Application Server](https://github.com/Phantom-fs/Herbify-Application-Server) repository. | Herbs have been used for centuries for their medicinal properties and culinary uses. Our website helps you identify over 90 types of common herbs found worldwide. Simply upload a photo of the herb you want to identify, and our DL model with help accurately classify the herb. | classification,css,deep-learning,deployed,detect,detection,herb,herbs,heroku,heroku-deployment | 2024-04-17T17:08:09Z | 2024-04-18T09:18:40Z | null | 2 | 0 | 4 | 0 | 0 | 4 | null | GPL-3.0 | CSS |
robertovicario/2UML | main | # 2UML
## Overview
2UML is an intuitive and efficient tool designed to streamline the process of creating Unified Modeling Language (UML) diagrams. With its user-friendly interface, 2UML empowers users to generate UML diagrams effortlessly from natural language inputs.
> [!NOTE]
>
> ### Try 2UML
>
> Ready to experience the simplicity? Try 2UML here: [robertovicario.github.io/2UML](https://robertovicario.github.io/2UML)
## Preview
<img src="https://github.com/robertovicario/2UML/assets/119845903/dac148e4-8e1a-4bd5-ac49-cf31427af7ac" width=512>
## License
This project is distributed under [GNU General Public License version 3](https://opensource.org/license/gpl-3-0). You can find the complete text of the license in the project repository.
> [!IMPORTANT]
>
> ### Credits
>
> We believe in acknowledging the contributions of those who have made this project possible. Below are the individuals and technologies that have played a significant role:
>
> - **plantuml:**
> - **Author:** [plantuml](https://github.com/plantuml)
> - **License:** [GNU General Public License version 3](https://opensource.org/license/gpl-3-0)
> - **Source:** [GitHub Repository](https://github.com/plantuml/plantuml)
>
> - **plantuml-core:**
> - **Author:** [plantuml](https://github.com/plantuml)
> - **License:** [The MIT License](https://opensource.org/license/mit)
> - **Source:** [GitHub Repository](https://github.com/plantuml/plantuml-core)
>
> - **CheerpJ:**
> - **Author:** [Leaning Technologies](https://leaningtech.com)
> - **License:** [CheerpJ Community License](https://labs.leaningtech.com/cheerpj3/licensing)
> - **Source:** [Website](https://cheerpj.com)
| A user-friendly tool that generates UMLs starting from natural language inputs. | diagrams,natural-language-processing,plantuml,uml,artificial-intelligence,bootstrap,javascript,css,html | 2024-04-06T18:42:51Z | 2024-04-25T12:51:29Z | null | 2 | 2 | 119 | 0 | 1 | 4 | null | GPL-3.0 | HTML |
No-Country/s14-09-ft-node-react | main | ## NOA 🎮
NOA una aplicación web construida con React y TypeScript que tiene como objetivo conectar a jugadores basados en sus intereses en los videojuegos. ¡Piensa en Tinder para jugadores! Los usuarios pueden iniciar sesión, navegar a través de perfiles de otros jugadores que comparten intereses similares en los videojuegos, enviar invitaciones y conectarse con ellos para iniciar conversaciones y potencialmente jugar juntos.
# Presentacion del proyecto
https://www.canva.com/design/DAGDJ9mMNic/KsSAtQUQDCFxzmpCArZVYg/edit
## ¿Dónde puedo encontrar la web?
https://noalone.vercel.app/
## Funcionalidades en el MVP
- **Autenticación de Usuarios**: Sistema de autenticación seguro que permite a los usuarios registrarse e iniciar sesión de forma segura.
- **Creación de Perfiles**: Los usuarios pueden crear perfiles con sus intereses en los videojuegos, géneros preferidos, plataformas y hábitos de juego.
- **Algoritmo de Coincidencia**: GameMate utiliza un algoritmo de coincidencia sofisticado para sugerir posibles compañeros de juego basados en intereses y preferencias compartidas.
- **Invitaciones**: Los usuarios pueden enviar y recibir invitaciones para conectarse con otros jugadores.
- **Funcionalidad de Chat**: Funcionalidad de chat en tiempo real que permite a los usuarios comunicarse con sus compañeros de juego y planificar sesiones de juego.
## Archivo Figma
https://www.figma.com/file/nJqaIrpq7y8bQQwYwCRBQv/S14-9-NodeJs-React?type=design&node-id=1%3A2&mode=design&t=HDSfIJmPfMkfAah5-1
## Autenticacion de Usuarios
## Creación de Perfiles
## Algoritmo de Coincidencia, Invitaciones y Funcionalidad de chat
## Stacks Project Manager 📁 📂
****
|||
|:---:|:---:|
| <img style="width: 100px; min-width: 100px" src="https://i.pcmag.com/imagery/reviews/04C2m2ye5UfXyb5x5WWIsZ4-19.fit_scale.size_760x427.v1625759628.png" >|Trello para gestionar las incidencias, epicas, historias de usuarios, tareas|
| <img style="width: 100px; min-width: 100px" src="https://i.pinimg.com/originals/36/98/41/369841848d679cef173ae2b0f5ed6e39.png" >|Miro, para presentar documentos, agendas de las Dailys y Meet|
| <img style="width: 100px; min-width: 100px" src="https://cdn2.unrealengine.com/what-is-discord-1920x1080-c3d90ca45f57.jpg" >| Creacion de canal Discord para la comunicacion del equipo de desarrollo|
| <img style="width: 100px; min-width: 100px" src="https://user-images.githubusercontent.com/68760595/164306020-120e8664-cb5b-459a-80a3-99e13b057b52.png" >| Uso de la metodologia Scrum para llevar el equipo a las mejores practicas |
## Stacks de Equipo UX/UI🎨
****
|||
|:---:|:---:|
| <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D12AQEutamvJAXtZw/article-cover_image-shrink_720_1280/0/1689973782139?e=1719446400&v=beta&t=C74qZoyr5JYJVt0UHLtedx7X2ViMRUpU3Q-PLO0Pnrc" >|Figma, Herramienta de Prototipado Agil|
| <img style="width: 100px; min-width: 100px" src="https://oshl.umh.es/files/2014/11/inkscapelogo.jpg" >|Editor de gráficos vectoriales libre|
| <img style="width: 100px; min-width: 100px" src="https://d2mug8yhikhiqv.cloudfront.net/wp-content/uploads/2017/08/23034455/google-sprint-book-logo.jpeg" >| Metodologia Design Sprint para manejar el prototipado agil para validacion con usuarios en pocos dias|
| <img style="width: 100px; min-width: 100px" src="https://i.pinimg.com/736x/74/6d/77/746d77ef9b49afd5ec2306d39592d01e.jpg" >| Canva para edicion de videos |
## Stacks de Equipo Frontend
****
|||
|:---:|:---:|
| <img style="width: 100px; min-width: 100px" src="https://sigdeletras.com/images/blog/202004_react_leaflet/react.png">|Una biblioteca de JavaScript para construir interfaces de usuario|
| <img style="width: 100px; min-width: 100px" src="https://cdn.neowin.com/news/images/uploaded/2024/03/1709760302_typescript_story.jpg">|Un superset de JavaScript tipado estáticamente que mejora la calidad del código y la productividad del desarrollador|
| <img style="width: 100px; min-width: 100px" src="https://miro.medium.com/v2/resize:fit:1400/1*TVd_sNhpc7JDPBHAsAOQZg.jpeg">|Enrutamiento declarativo para aplicaciones React.|
| <img style="width: 100px; min-width: 100px" src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTMsPgbj3cubMDZPt8HwrkIBbf4AKUK1lY_ow&usqp=CAU">|Comunicación en tiempo real para funcionalidad de chat|
## Stacks de Equipo Backend
****
|||
|:---:|:---:|
| <img style="width: 100px; min-width: 100px" src="https://qualitapps.com/wp-content/uploads/2023/02/102.png">| Node Expres|
| <img style="width: 100px; min-width: 100px" src="https://kinsta.com/wp-content/uploads/2022/02/postgres-logo.png">|Postgresql|
## Stacks de Equipo QA Tester
****
|||
|:---:|:---:|
| <img style="width: 100px; min-width: 100px" src="https://miro.medium.com/v2/resize:fit:1200/1*HJpcblBvD8MpqAEZZXWVgg.png">|Selenium con Python|
| <img style="width: 100px; min-width: 100px" src="https://e7.pngegg.com/pngimages/187/698/png-clipart-software-testing-software-quality-assurance-software-development-computer-software-software-miscellaneous-people.png">|Pruebas Automatizadas|
## Agradecimientos
**************
## Equipo de desarrollo
|**QA**|**Backend**|**Frontend**|**UI/UX**|**Project Manager/TeamLider**|
|:---:|:---:|:---:|:---:|:---:|
|**Llorente Gabriel <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D03AQG0bw8qs55vsw/profile-displayphoto-shrink_800_800/0/1704755057748?e=1719446400&v=beta&t=rjBJC2k5Jmp-9gjwv38Ym5GT5OH8HKQuKWia8XxxumM" > <a href="https://www.linkedin.com/in/gabriel-llorente-testing-qa/"> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Javier Damiani <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D35AQFC0NodlpGaLQ/profile-framedphoto-shrink_800_800/0/1708731432186?e=1714615200&v=beta&t=CRk48-KTUaIzAPZTh9iuvHkBJE2YXjy7iP4asfOkInc" > <a href="https://www.linkedin.com/in/javierluisdamianiarellano/"> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Maximo Valfre <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D35AQFWfjmMws78LQ/profile-framedphoto-shrink_800_800/0/1712585986445?e=1714615200&v=beta&t=Hcvt527qBta7isNiWQ-mQZ7GrqH0J4mPmuDVDjlN_3c" > <a href="https://www.linkedin.com/in/maxivalfre/"> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Alex Montero <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4E35AQGa_gfYTm53zg/profile-framedphoto-shrink_800_800/0/1708480896935?e=1714615200&v=beta&t=OjJ0GLIAeqhh56TyRnK4adHHpMLswMHp8Ge1kTnK4jY" > <a href="https://www.linkedin.com/in/aleacx/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Johana Baccei <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D03AQFOFDOIEkc4pA/profile-displayphoto-shrink_800_800/0/1678317652369?e=1719446400&v=beta&t=EwhC6rVZamop3aPWviZyIaJiyvH4NyyxnFTOV3rwT_8" > <a href="https://www.linkedin.com/in/johana-baccei-11b005248/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|
|**Cinthia Gutiérrez <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4E35AQG9CgHK9DTu5A/profile-framedphoto-shrink_800_800/0/1684221346128?e=1714615200&v=beta&t=q2YA0sO3tbuqocXtja0zUWWdAfBQ2r6-wBpwTqci-JY" > <a href="https://www.linkedin.com/in/cinthia-guti%C3%A9rrez-vargas-ti/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Fernando Torron <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D35AQF3Q5gzjjdhYg/profile-framedphoto-shrink_800_800/0/1678826675763?e=1714615200&v=beta&t=qVlcYnKs08UfN-LfIBhqzTuHEWILqORhzl9KgiFrm98" > <a href="https://www.linkedin.com/in/fertorron/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Matías Campos <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D35AQGaoJ9_k2SdbQ/profile-framedphoto-shrink_800_800/0/1705784310092?e=1714615200&v=beta&t=bn6p1lyt2XcRx4g97n0YzB_XT7X_UJ9IvVh4CyenhG8" > <a href="https://www.linkedin.com/in/mat%C3%ADas-agust%C3%ADn-campos/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Michellangela Sierra <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D03AQHX-i5NrmzdgA/profile-displayphoto-shrink_800_800/0/1710553752281?e=1719446400&v=beta&t=hT71TUI2l-R893rProKZO-AnDWF5CzmmHDWmGlzGR4w" > <a href="https://www.linkedin.com/in/michellesierra/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**
||**Gabriel Mancilla <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/C4D03AQEoBtTXNXxsTA/profile-displayphoto-shrink_800_800/0/1644691132895?e=1719446400&v=beta&t=ICeLTQ7E6BaRg6BsUOp_D4wBVMlhIDfkMpshOl0LA2s"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Wagner Dueñas <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D5603AQEeE5xBumFmmA/profile-displayphoto-shrink_800_800/0/1703193203546?e=1719446400&v=beta&t=BJkoAAidHJDE13Ot14k5s9uWvpUnIRZOHEjR_34RnYM" > <a href="https://www.linkedin.com/in/wsmith123/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**|**Noelia Sciorra <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D35AQGDDGpL1iMSng/profile-framedphoto-shrink_800_800/0/1623342640437?e=1714618800&v=beta&t=W47_GGQPGfRnkgSM-Tj6zci67o4mz8En_Ohij2QK8Iw" > <a href="https://www.linkedin.com/in/noelia-sciorra/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**
|||**Welinton Suarez <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4E03AQFN404nJ2RU4Q/profile-displayphoto-shrink_800_800/0/1692315083037?e=1719446400&v=beta&t=6c88-dH7-2m5bjz06M7XHACmJKBcc80iT_IZnOg5ct0" > <a href="https://www.linkedin.com/in/welinton-suarez/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**
|||**Nicolas Fontanini <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4D03AQEg8UHaPo6g3g/profile-displayphoto-shrink_800_800/0/1693338952203?e=1719446400&v=beta&t=othR4lZhjQcCc31SF9jaP4cO_PapjuNF6eGuMgSq1Dw" > <a href="https://www.linkedin.com/in/nicolasfontanini/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**
|||**Tomas Laus <img style="width: 100px; min-width: 100px" src="https://media.licdn.com/dms/image/D4E03AQHuTO_1-wdAhg/profile-displayphoto-shrink_800_800/0/1698090767557?e=1719446400&v=beta&t=rbTarSasKNoI3s-eZrl5LcA6B0WkZh1RTAxeCOymvzk" > <a href="https://www.linkedin.com/in/tomaslaus/"> <br> <img style="width: 50px; min-width: 50px" src="https://blog.b2bstack.com.br/wp-content/uploads/2022/11/LinkedIn-simbolo.jpg">**
| Noa - Never One Alone | Web App de Matcheo de Videojuegos! | css,javascript,postgresql,postman,qase,react,tableplus,tailwindcss,typescript,node-express | 2024-03-29T16:19:54Z | 2024-05-07T16:33:48Z | null | 17 | 50 | 275 | 0 | 0 | 4 | null | null | TypeScript |
maxwalks/nodejs-ip-grabber | main | # NodeJS Ip Grabber
## Description
ExpressJS app that requests the user's headers, where the originating ip address is located. This gets sent to a discord webhook with aditional information such as: country, region, timezone and city. The region and the city will not be accurate 90% of the time.
## Create .env file
Create a .env file to store the webhook link. Example below:
```
WEBHOOK_URI = https://discord.com/api/webhooks/xxxxxxxxxxx/xxxxxxxxxxxx
```
## Installation
To install and run this project - install dependencies using npm and then start your server.
```
$ npm install
$ npm run dev
```
## Credits
Thanks to the [evilportals github](https://github.com/kleo/evilportals), i could include the google signup page. Please check it out.
| Fetch any user's ip address, just by clicking the site. | discord-webhook,expressjs,ip,javascript,nodejs | 2024-04-28T14:07:22Z | 2024-04-29T16:30:40Z | null | 1 | 0 | 12 | 0 | 0 | 4 | null | null | CSS |
GunaPalanivel/Modern-JavaScript-Fundamentals | main | # JavaScript Fundamentals
JavaScript is one of the most popular programming languages, and it has become increasingly powerful since the introduction of ES6 in 2014. This project is designed to help you learn the fundamental concepts of JavaScript, including Variables & Data Types, Operators & Equality, Logic & Control Flow, and Functions.
**For More Information on JavaScript heads to [javascript.md](javascript.md)**
## Table of Contents
**Paths to the GitHub Folder for each section**
1. [Environment Setup](https://github.com/gp5901/Modern-JavaScript-Fundamentals/tree/main/01-Introduction)
2. [Variables and Data Types](https://github.com/gp5901/Modern-JavaScript-Fundamentals/tree/main/02-VariablesAndDataTypes)
3. [Operators and Equality](https://github.com/gp5901/Modern-JavaScript-Fundamentals/tree/main/03-OperatorsAndEquality)
4. [Logic and Control Flow](https://github.com/gp5901/Modern-JavaScript-Fundamentals/tree/main/04-LogicAndControlFlow)
5. [Functions](https://github.com/gp5901/Modern-JavaScript-Fundamentals/tree/main/05-Functions)
## Via GitHub Pages (Website)
## [Environment Setup](./01-Introduction/README.md)
- [Source Code Editor For Web Development](./01-Introduction/SourceCodeEditorForWebDevelopment.md)
- [Getting Started with Visual Studio Code for JavaScript and Web Development](./01-Introduction/VisualStudioCodeSetup.md)
- [Guide: Getting Started with Chrome and Developer Tools for JavaScript Web Development](./01-Introduction/WebBrowserForWebDevelopment.md)
This project is designed to be used with Visual Studio Code, a popular code editor. You should also install the following [Visual Studio Code extensions and Change the settings](https://github.com/GunaPalanivel/vs-code-settings) for a better coding experience.
## [Variables and Data Types](./02-VariablesAndDataTypes/README.md)
In this section, you will learn about:
- [Variables](./02-VariablesAndDataTypes/01-Variables/Variables.md)
- [Data Types (Strings, Numbers, Booleans, Null, Undefined, Objects)](./02-VariablesAndDataTypes/02-DataTypes/DataTypes.md)
- [Statically vs. Dynamically Typed Languages](./02-VariablesAndDataTypes/02-DataTypes/DataTypes.md)
## [Operators and Equality](./03-OperatorsAndEquality/README.md)
This section covers:
**[Operators and Equality](./03-OperatorsAndEquality/OperatorsAndEquality.md)**
- Arithmetic Operators
- Comparison Operators and Equality
- Strict vs. Loose Equality
- Logical Operators
- Assignment Operators
## Logic and Control Flow
In this section, you will explore:
**[Logic and Control Flow](./04-LogicAndControlFlow/LogicAndControlFlow.md)**
- If Statements
- Truthy and Falsy Values
- Logical Operators (Part 2)
- Switch Statement
- Ternary Operator
- Loops (While and For)
## Functions
This section focuses on:
**[Functions](./05-Functions/Functions.md)**
- Declaring and Invoking Functions
- Function Return
- Arrow Functions
- Parameters vs. Arguments
## Contributing
If you have any suggestions or find any issues, feel free to open a new issue or submit a pull request.
## License
This project is licensed under the [MIT License](LICENSE).
---
This README.md file provides a basic structure for this JavaScript Fundamentals project.
## Developer
This project was developed by [Guna Palanivel](https://www.linkedin.com/in/guna-palanivel/).
**For More Information heads to [GitHub Folder](https://github.com/GunaPalanivel/Modern-JavaScript-Fundamentals.git).**
| JavaScript is one of the most popular languages of all time, it is easy to learn and it is extremely powerful. In this Repo, you will learn the fundamentals of JavaScript including Variables & Data Types, Operators & Equality, Logic & Control Flow, and Functions. This Repo is written in modern JavaScript (ES6+) including all of the newest features. | javascript | 2024-03-29T06:09:22Z | 2024-05-19T05:44:03Z | null | 3 | 1 | 44 | 0 | 1 | 4 | null | MIT | JavaScript |
Eddie-OConnor/personal-site | main | # personal-react-site V1
Simple and responsive professional website for software-engineers to showcase projects, display contact information, and tell your story.
<strong>👀 <a href="https://eddie-oconnor.com/" target="_blank">Live Site Demo</a></strong>
<br/>
<center>
<img src="public\homepage-screenshot.png" alt="personal-react-site image" />
</center>
- [Features](#-features)
- [Installation and Setup](#-installation-and-setup)
- [Structure](#-structure)
- [Quick Configurations](#-quick-configurations)
- [Launch](#-launching-the-site-with-cloudflare)
- [Future improvements and Contributions](#-future-improvements-and-contributions)
## 📙 Features
- 📖 Multi-Page
- Home
- About
- Projects
- Contact
- 📱 Fully Responsive
- 🛠 Easy configurations
## 🛠 Installation and Setup
1. Clone the repository
2. Ensure `NodeJS` and `git` are installed on your computer
2. Run `npm install` in the terminal
3. Then run `npm start` which will run the app in development mode and open a new browser tab
4. If the browser does not automatically open, look for the local port url in the terminal which will look something like this `Local:http://localhost:3000`
5. Make changes and see them reflected in the browser when saved
6. Continued instructions for novice coders in the [Quick Configurations](#-quick-configurations) section
## 📁 Structure
- `/public`: publicly accessible media (i.e. images)
- use [favicon](https://favicon.io/) to update your own picture(s) for site tab icons
- `/src`: all the components used in this project
- `/src/components/`: houses each page (`/src/pages`), shared components (i.e. navbar) and their respective css styles
- `/src/data`: make quick global configurations here
## ⚙️ Quick Configurations
- Directory: `/src/data/` - Your changes in these files will be reflected upon save in the local development browser you opened in a previous step.
- `user.js` - Update the displayed text and images throughout the site by simply updating each field to the desired text or image file path.
- `styles.css` - Change the font colors and font families of the whole application without editing any other code files. Simply erase the values, input a new color or font, then hit save.
- [Here](https://www.w3schools.com/colors/colors_picker.asp) is a good tool to see and copy color codes to input below when using `styles.css`
- Visit [Google Fonts](https://fonts.google.com/) to browse and select fonts by adding them to your cart. View your selected families, then click `<> get embed code` and select `@import` to copy/paste your new import url into `index.css`. You will then be able to globally update the site's fonts by choosing new primary and secondary fonts in `styles.css`
<br/>
```css
:root {
/* ------- colors ------- */
--primary-color: #27272a;
--secondary-color: #65656d;
--tertiary-color: #acacb4;
--quaternary-color: #e4e4e7;
--link-color: #14b8a6;
/* ---------------------- */
/* ------- fonts ------- */
--primary-font: "Heebo", sans-serif;
--secondary-font: "Roboto", sans-serif;
/* --------------------- */
}
```
## 🚀 Launching the Site with Cloudflare
1. Create Cloudflare account
2. Navigate to Workers & Pages
3. Create new page
4. Connect to your cloned Git repo
5. Input `npm run build` as build command and `build` as location
6. Investigate setting up a custom URL (optional)
## 🌱 Future improvements and Contributions
I welcome any and all feedback and ideas from seasoned developers and novice users! Please reference `github\templates` when doing so. | Simple and responsive professional React website for software-engineers to showcase projects, display contact information, and tell your story. | cloudflare,css,javascript,portfolio-template,portfolio-website,react,react-portfolio,react-portfolio-template,responsive-design | 2024-03-31T17:03:05Z | 2024-04-09T14:14:48Z | null | 1 | 0 | 51 | 0 | 0 | 4 | null | null | JavaScript |
AmulyaMachhan/currencyConverter | master | # Currency Converter Website
Welcome to the Currency Converter Website! This project is built using React and Vite, allowing users to convert currencies effortlessly.
You can view this site [here](https://amulyamachhan.github.io/currencyConverter/).
## Screenshot
## Features
- **Currency Conversion:** Convert currency from one type to another.
- **Extensive Currency Options:** Supports almost all currencies.
- **Swap Functionality:** Easily switch between source and target currencies.
## Technologies Used
- React
- Vite
- JavaScript (ES6+)
- Tailwind CSS
- HTML5
- CSS3
## Getting Started
### Prerequisites
Before running this project, ensure that you have Node.js and npm (or yarn) installed on your machine.
### Installation
1. Clone this repository to your local machine:
```
git clone https://github.com/AmulyaMachhan/currencyConverter.git
```
2. Navigate to the project directory:
```
cd currency-converter
```
3. Install the dependencies:
```
npm install
```
or
```
yarn install
```
### Usage
1. Start the development server:
```
npm run dev
```
or
```
yarn dev
```
2. Open your web browser and go to `http://localhost:3000` to view the currency converter website.
## Contributing
Contributions are welcome! If you'd like to contribute to this project, feel free to submit a pull request.
| Currency Converter Website! This project is built using React and Vite, allowing users to convert currencies effortlessly. | css,custom-hook,github-deployment,html,javascript,react,react-hooks,tailwindcss,use-effect,use-state | 2024-04-14T12:04:51Z | 2024-04-23T22:02:18Z | null | 1 | 0 | 5 | 0 | 0 | 3 | null | null | JavaScript |
zahidrahimoon/BrainwaveClone | master | ## <a name="introduction">🤖 Introduction</a>
Brainwave - Clone of Modern UI/UX website, developed using React.js and Tailwind CSS, exemplifies modern UI/UX principles. Its sleek design, seamless animations, and overall user experience set a high standard, serving as a reference or inspiration for future modern applications or websites in general.
## <a name="tech-stack">⚙️ Tech Stack</a>
- Vite
- React.js
- Tailwind CSS
## <a name="features">🔋 Features</a>
👉 **Beautiful Sections**: Includes hero, services, features, how to use, roadmap, pricing, footer, and header.
👉 **Parallax Animations**: Engaging effects triggered by mouse movement and scrolling
👉 **Complex UI Geometry**: Utilizes tailwindcss for intricate shapes like circular feature displays, grid lines, and side lines.
👉 **Latest UI Trends**: Incorporates modern design elements such as bento grids.
👉 **Cool Gradients**: Enhances visuals with stylish gradients using Tailwind CSS for cards, buttons, etc.
👉 **Responsive**: Ensures seamless functionality and aesthetics across all devices
and many more, including code architecture and reusability.
## <a name="quick-start">🤸 Quick Start</a>
Follow these steps to set up the project locally on your machine.
**Prerequisites**
Make sure you have the following installed on your machine:
- [Git](https://git-scm.com/)
- [Node.js](https://nodejs.org/en)
- [npm](https://www.npmjs.com/) (Node Package Manager)
**Cloning the Repository**
```bash
git clone https://github.com/zahidrahimoon/BrainwaveClone.git
cd brainwave
```
**Installation**
Install the project dependencies using npm:
```bash
npm install
```
**Running the Project**
```bash
npm run dev
```
Open [http://localhost:5173](http://localhost:5173) in your browser to view the project.
## <a name="snippets">🕸️ Snippets</a>
<details>
<summary><code>.vscode/settings.json</code></summary>
```json
{
"editor.defaultFormatter": "esbenp.prettier-vscode",
"editor.formatOnSave": true,
"editor.codeActionsOnSave": {
"source.fixAll.eslint": "explicit",
"source.addMissingImports": "explicit"
},
"prettier.tabWidth": 2,
"prettier.useTabs": false,
"prettier.semi": true,
"prettier.singleQuote": false,
"prettier.jsxSingleQuote": false,
"prettier.trailingComma": "es5",
"prettier.arrowParens": "always",
"[javascriptreact]": {
"editor.defaultFormatter": "esbenp.prettier-vscode"
},
"[css]": {
"editor.defaultFormatter": "vscode.css-language-features"
},
"[svg]": {
"editor.defaultFormatter": "jock.svg"
}
}
```
</details>
<details>
<summary><code>tailwind.config.js</code></summary>
```javascript
/** @type {import('tailwindcss').Config} */
import { fontFamily } from "tailwindcss/defaultTheme";
import plugin from "tailwindcss/plugin";
export default {
content: [
"./index.html",
"./src/**/*.{js,ts,jsx,tsx}",
"./public/assets/**/*.{js,ts,jsx,tsx}",
],
theme: {
extend: {
colors: {
color: {
1: "#AC6AFF",
2: "#FFC876",
3: "#FF776F",
4: "#7ADB78",
5: "#858DFF",
6: "#FF98E2",
},
stroke: {
1: "#26242C",
},
n: {
1: "#FFFFFF",
2: "#CAC6DD",
3: "#ADA8C3",
4: "#757185",
5: "#3F3A52",
6: "#252134",
7: "#15131D",
8: "#0E0C15",
9: "#474060",
10: "#43435C",
11: "#1B1B2E",
12: "#2E2A41",
13: "#6C7275",
},
},
fontFamily: {
sans: ["var(--font-sora)", ...fontFamily.sans],
code: "var(--font-code)",
grotesk: "var(--font-grotesk)",
},
letterSpacing: {
tagline: ".15em",
},
spacing: {
0.25: "0.0625rem",
7.5: "1.875rem",
15: "3.75rem",
},
opacity: {
15: ".15",
},
transitionDuration: {
DEFAULT: "200ms",
},
transitionTimingFunction: {
DEFAULT: "linear",
},
zIndex: {
1: "1",
2: "2",
3: "3",
4: "4",
5: "5",
},
borderWidth: {
DEFAULT: "0.0625rem",
},
backgroundImage: {
"radial-gradient": "radial-gradient(var(--tw-gradient-stops))",
"conic-gradient":
"conic-gradient(from 225deg, #FFC876, #79FFF7, #9F53FF, #FF98E2, #FFC876)",
"benefit-card-1": "url(assets/benefits/card-1.svg)",
"benefit-card-2": "url(assets/benefits/card-2.svg)",
"benefit-card-3": "url(assets/benefits/card-3.svg)",
"benefit-card-4": "url(assets/benefits/card-4.svg)",
"benefit-card-5": "url(assets/benefits/card-5.svg)",
"benefit-card-6": "url(assets/benefits/card-6.svg)",
},
},
},
plugins: [
plugin(function ({ addBase, addComponents, addUtilities }) {
addBase({});
addComponents({
".container": {
"@apply max-w-[77.5rem] mx-auto px-5 md:px-10 lg:px-15 xl:max-w-[87.5rem]":
{},
},
".h1": {
"@apply font-semibold text-[2.5rem] leading-[3.25rem] md:text-[2.75rem] md:leading-[3.75rem] lg:text-[3.25rem] lg:leading-[4.0625rem] xl:text-[3.75rem] xl:leading-[4.5rem]":
{},
},
".h2": {
"@apply text-[1.75rem] leading-[2.5rem] md:text-[2rem] md:leading-[2.5rem] lg:text-[2.5rem] lg:leading-[3.5rem] xl:text-[3rem] xl:leading-tight":
{},
},
".h3": {
"@apply text-[2rem] leading-normal md:text-[2.5rem]": {},
},
".h4": {
"@apply text-[2rem] leading-normal": {},
},
".h5": {
"@apply text-2xl leading-normal": {},
},
".h6": {
"@apply font-semibold text-lg leading-8": {},
},
".body-1": {
"@apply text-[0.875rem] leading-[1.5rem] md:text-[1rem] md:leading-[1.75rem] lg:text-[1.25rem] lg:leading-8":
{},
},
".body-2": {
"@apply font-light text-[0.875rem] leading-6 md:text-base": {},
},
".caption": {
"@apply text-sm": {},
},
".tagline": {
"@apply font-grotesk font-light text-xs tracking-tagline uppercase":
{},
},
".quote": {
"@apply font-code text-lg leading-normal": {},
},
".button": {
"@apply font-code text-xs font-bold uppercase tracking-wider": {},
},
});
addUtilities({
".tap-highlight-color": {
"-webkit-tap-highlight-color": "rgba(0, 0, 0, 0)",
},
});
}),
],
};
```
</details>
<details>
<summary><code>index.css</code></summary>
```css
@import url("https://fonts.googleapis.com/css2?family=Sora:wght@300;400;600&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Source+Code+Pro:wght@400;600;700&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@300&display=swap");
@tailwind base;
@tailwind components;
@tailwind utilities;
:root {
--font-sora: "Sora", sans-serif;
--font-code: "Source Code Pro", monospace;
--font-grotesk: "Space Grotesk", sans-serif;
}
* {
scroll-behavior: smooth;
}
@layer base {
body {
@apply font-sans bg-n-8 text-n-1 text-base;
}
}
.rotate-45 {
@apply rotate-[45deg];
}
.rotate-90 {
@apply rotate-[90deg];
}
.rotate-135 {
@apply rotate-[135deg];
}
.rotate-180 {
@apply rotate-[180deg];
}
.rotate-225 {
@apply rotate-[225deg];
}
.rotate-270 {
@apply rotate-[270deg];
}
.rotate-315 {
@apply rotate-[315deg];
}
.rotate-360 {
@apply rotate-[360deg];
}
.-rotate-45 {
@apply rotate-[-45deg];
}
.-rotate-90 {
@apply rotate-[-90deg];
}
.-rotate-135 {
@apply rotate-[-135deg];
}
.-rotate-180 {
@apply rotate-[-180deg];
}
.-rotate-225 {
@apply rotate-[-225deg];
}
.-rotate-270 {
@apply rotate-[-270deg];
}
.-rotate-315 {
@apply rotate-[-315deg];
}
.-rotate-360 {
@apply rotate-[-360deg];
}
```
</details>
<details>
<summary><code>constants/index.js</code></summary>
```javascript
import {
benefitIcon1,
benefitIcon2,
benefitIcon3,
benefitIcon4,
benefitImage2,
chromecast,
disc02,
discord,
discordBlack,
facebook,
figma,
file02,
framer,
homeSmile,
instagram,
notification2,
notification3,
notification4,
notion,
photoshop,
plusSquare,
protopie,
raindrop,
recording01,
recording03,
roadmap1,
roadmap2,
roadmap3,
roadmap4,
searchMd,
slack,
sliders04,
telegram,
twitter,
yourlogo,
} from "../../public/assets";
export const navigation = [
{
id: "0",
title: "Features",
url: "#features",
},
{
id: "1",
title: "Pricing",
url: "#pricing",
},
{
id: "2",
title: "How to use",
url: "#how-to-use",
},
{
id: "3",
title: "Roadmap",
url: "#roadmap",
},
{
id: "4",
title: "New account",
url: "#signup",
onlyMobile: true,
},
{
id: "5",
title: "Sign in",
url: "#login",
onlyMobile: true,
},
];
export const heroIcons = [homeSmile, file02, searchMd, plusSquare];
export const notificationImages = [notification4, notification3, notification2];
export const companyLogos = [yourlogo, yourlogo, yourlogo, yourlogo, yourlogo];
export const brainwaveServices = [
"Photo generating",
"Photo enhance",
"Seamless Integration",
];
export const brainwaveServicesIcons = [
recording03,
recording01,
disc02,
chromecast,
sliders04,
];
export const roadmap = [
{
id: "0",
title: "Voice recognition",
text: "Enable the chatbot to understand and respond to voice commands, making it easier for users to interact with the app hands-free.",
date: "May 2023",
status: "done",
imageUrl: roadmap1,
colorful: true,
},
{
id: "1",
title: "Gamification",
text: "Add game-like elements, such as badges or leaderboards, to incentivize users to engage with the chatbot more frequently.",
date: "May 2023",
status: "progress",
imageUrl: roadmap2,
},
{
id: "2",
title: "Chatbot customization",
text: "Allow users to customize the chatbot's appearance and behavior, making it more engaging and fun to interact with.",
date: "May 2023",
status: "done",
imageUrl: roadmap3,
},
{
id: "3",
title: "Integration with APIs",
text: "Allow the chatbot to access external data sources, such as weather APIs or news APIs, to provide more relevant recommendations.",
date: "May 2023",
status: "progress",
imageUrl: roadmap4,
},
];
export const collabText =
"With smart automation and top-notch security, it's the perfect solution for teams looking to work smarter.";
export const collabContent = [
{
id: "0",
title: "Seamless Integration",
text: collabText,
},
{
id: "1",
title: "Smart Automation",
},
{
id: "2",
title: "Top-notch Security",
},
];
export const collabApps = [
{
id: "0",
title: "Figma",
icon: figma,
width: 26,
height: 36,
},
{
id: "1",
title: "Notion",
icon: notion,
width: 34,
height: 36,
},
{
id: "2",
title: "Discord",
icon: discord,
width: 36,
height: 28,
},
{
id: "3",
title: "Slack",
icon: slack,
width: 34,
height: 35,
},
{
id: "4",
title: "Photoshop",
icon: photoshop,
width: 34,
height: 34,
},
{
id: "5",
title: "Protopie",
icon: protopie,
width: 34,
height: 34,
},
{
id: "6",
title: "Framer",
icon: framer,
width: 26,
height: 34,
},
{
id: "7",
title: "Raindrop",
icon: raindrop,
width: 38,
height: 32,
},
];
export const pricing = [
{
id: "0",
title: "Basic",
description: "AI chatbot, personalized recommendations",
price: "0",
features: [
"An AI chatbot that can understand your queries",
"Personalized recommendations based on your preferences",
"Ability to explore the app and its features without any cost",
],
},
{
id: "1",
title: "Premium",
description: "Advanced AI chatbot, priority support, analytics dashboard",
price: "9.99",
features: [
"An advanced AI chatbot that can understand complex queries",
"An analytics dashboard to track your conversations",
"Priority support to solve issues quickly",
],
},
{
id: "2",
title: "Enterprise",
description: "Custom AI chatbot, advanced analytics, dedicated account",
price: null,
features: [
"An AI chatbot that can understand your queries",
"Personalized recommendations based on your preferences",
"Ability to explore the app and its features without any cost",
],
},
];
export const benefits = [
{
id: "0",
title: "Ask anything",
text: "Lets users quickly find answers to their questions without having to search through multiple sources.",
backgroundUrl: "assets/benefits/card-1.svg",
iconUrl: benefitIcon1,
imageUrl: benefitImage2,
},
{
id: "1",
title: "Improve everyday",
text: "The app uses natural language processing to understand user queries and provide accurate and relevant responses.",
backgroundUrl: "assets/benefits/card-2.svg",
iconUrl: benefitIcon2,
imageUrl: benefitImage2,
light: true,
},
{
id: "2",
title: "Connect everywhere",
text: "Connect with the AI chatbot from anywhere, on any device, making it more accessible and convenient.",
backgroundUrl: "assets/benefits/card-3.svg",
iconUrl: benefitIcon3,
imageUrl: benefitImage2,
},
{
id: "3",
title: "Fast responding",
text: "Lets users quickly find answers to their questions without having to search through multiple sources.",
backgroundUrl: "assets/benefits/card-4.svg",
iconUrl: benefitIcon4,
imageUrl: benefitImage2,
light: true,
},
{
id: "4",
title: "Ask anything",
text: "Lets users quickly find answers to their questions without having to search through multiple sources.",
backgroundUrl: "assets/benefits/card-5.svg",
iconUrl: benefitIcon1,
imageUrl: benefitImage2,
},
{
id: "5",
title: "Improve everyday",
text: "The app uses natural language processing to understand user queries and provide accurate and relevant responses.",
backgroundUrl: "assets/benefits/card-6.svg",
iconUrl: benefitIcon2,
imageUrl: benefitImage2,
},
];
export const socials = [
{
id: "0",
title: "Discord",
iconUrl: discordBlack,
url: "#",
},
{
id: "1",
title: "Twitter",
iconUrl: twitter,
url: "#",
},
{
id: "2",
title: "Instagram",
iconUrl: instagram,
url: "#",
},
{
id: "3",
title: "Telegram",
iconUrl: telegram,
url: "#",
},
{
id: "4",
title: "Facebook",
iconUrl: facebook,
url: "#",
},
];
```
</details>
<details>
<summary><code>components/Section.jsx</code></summary>
```javascript
import SectionSvg from "../../public/assets/svg/SectionSvg";
const Section = ({
className,
id,
crosses,
crossesOffset,
customPaddings,
children,
}) => (
<div
id={id}
className={`relative
${
customPaddings ||
`py-10 lg:py-16 xl:py-20 ${crosses ? "lg:py-32 xl:py-40" : ""}`
} ${className || ""}`}
>
{children}
<div className="hidden absolute top-0 left-5 w-0.25 h-full bg-stroke-1 pointer-events-none md:block lg:left-7.5 xl:left-10" />
<div className="hidden absolute top-0 right-5 w-0.25 h-full bg-stroke-1 pointer-events-none md:block lg:right-7.5 xl:right-10" />
{crosses && (
<>
<div
className={`hidden absolute top-0 left-7.5 right-7.5 h-0.25 bg-stroke-1 ${
crossesOffset && crossesOffset
} pointer-events-none lg:block xl:left-10 right-10`}
/>
<SectionSvg crossesOffset={crossesOffset} />
</>
)}
</div>
);
export default Section;
```
</details>
<details>
<summary><code>components/Roadmap.jsx</code></summary>
```javascript
import Button from "./Button";
import Heading from "./Heading";
import Section from "./Section";
import Tagline from "./TagLine";
import { roadmap } from "../constants";
import { check2, grid, loading1 } from "../../public/assets";
import { Gradient } from "./design/Roadmap";
const Roadmap = () => (
<Section className="overflow-hidden" id="roadmap">
<div className="container md:pb-10">
<Heading tag="Ready to get started" title="What we’re working on" />
<div className="relative grid gap-6 md:grid-cols-2 md:gap-4 md:pb-[7rem]">
{roadmap.map((item) => {
const status = item.status === "done" ? "Done" : "In progress";
return (
<div
className={`md:flex even:md:translate-y-[7rem] p-0.25 rounded-[2.5rem] ${
item.colorful ? "bg-conic-gradient" : "bg-n-6"
}`}
key={item.id}
>
<div className="relative p-8 bg-n-8 rounded-[2.4375rem] overflow-hidden xl:p-15">
<div className="absolute top-0 left-0 max-w-full">
<img
className="w-full"
src={grid}
width={550}
height={550}
alt="Grid"
/>
</div>
<div className="relative z-1">
<div className="flex items-center justify-between max-w-[27rem] mb-8 md:mb-20">
<Tagline>{item.date}</Tagline>
<div className="flex items-center px-4 py-1 bg-n-1 rounded text-n-8">
<img
className="mr-2.5"
src={item.status === "done" ? check2 : loading1}
width={16}
height={16}
alt={status}
/>
<div className="tagline">{status}</div>
</div>
</div>
<div className="mb-10 -my-10 -mx-15">
<img
className="w-full"
src={item.imageUrl}
width={628}
height={426}
alt={item.title}
/>
</div>
<h4 className="h4 mb-4">{item.title}</h4>
<p className="body-2 text-n-4">{item.text}</p>
</div>
</div>
</div>
);
})}
<Gradient />
</div>
<div className="flex justify-center mt-12 md:mt-15 xl:mt-20">
<Button href="/roadmap">Our roadmap</Button>
</div>
</div>
</Section>
);
export default Roadmap;
```
</details>
## <a name="links">🔗 Links</a>
- [Assets](https://drive.google.com/file/d/1JKzwPl_hnpjIlNbwfjMagb4HosxnyXbf/view?usp=sharing)
- [Design](https://drive.google.com/file/d/15WJMOchujvaQ7Kg9e0nGeGR7G7JOeX1K/view?usp=sharing)
- [Absolute Relative Positioning](https://css-tricks.com/absolute-positioning-inside-relative-positioning/)
- [Live Website](http://brainwaveclone.netlify.app)
| "Brainwave is a modern UI design project built with React and Tailwind CSS, combining sleek aesthetics with responsive functionality for a seamless user experience." | brainwave,javascript,landing-page,react,react-hooks,reactjs,taiwlindcss,webdevelopment,website,brainwaveclone | 2024-03-15T05:52:32Z | 2024-04-02T18:10:31Z | null | 1 | 0 | 5 | 0 | 0 | 3 | null | null | JavaScript |
mihairusu88/nextjs-booking | master | # Next.js booking application
> Create a next.js home services booking application.
## Quick Start
```bash
# Install dependencies
npm install
# Run development server
npm run dev
# Run production build
npm run build
# Server runs on http://localhost:3000
```
### Check live demo on netlify.
[](https://app.netlify.com/sites/nextjs-home-services-booking/deploys)
[Live Demo](https://nextjs-home-services-booking.netlify.app/)
| Next.js booking application | booking,booking-system,google-maps-api,javascript,location,location-services,nextjs,oauth2,oauth2-server,prisma | 2024-03-21T13:49:43Z | 2024-03-21T15:59:25Z | null | 1 | 0 | 8 | 1 | 2 | 3 | null | null | TypeScript |
Dheerajjha451/Meet_Your_Pet | main | <div align="center">
# Meet_Your_Pet
</div>
## About
**Meet Your Pet** is not just a web application, It's a bridge between loving homes and our furry friends waiting for their forever famillies. With the help of cutting edge technologies, our application offers a unique way to help a stray dog meet a heartwarming family.
## How to Use?
**Snap a Photo**:- Take a clear picture of the dog you're are curious about or you encountered on the street.
**Upload and Predict**:- Upload the image to meet your pet and predict to know the breed and description of the dog.
**Connect to Adoption Agencies**:- Several Adoption agencies will be listed with the dog available, Connect with them for the further proceedings.
# Running Meet Your Pet
**Meet Your Pet** is developed using React js for frontend and Flask for backend.
The model is trained using transfer learning using the **MobilenetV2** Architecture with an accuracy of **0.9853515625**.
## Running the Backend
### Setup
1. Navigate to the `Backend` directory:
```
cd Meet_Your_Pet/Backend
```
2. Install the required Python packages:
```
pip install -r requirements.txt
```
### Starting the Server
3. Run the backend server:
```
python app.py
```
The backend server should now be running and ready to handle requests.
## Running the Frontend
### Setup
1. Navigate to the `frontend` directory:
```
cd Meet_Your_Pet/frontend
```
2. Install the required Node.js packages:
```
npm install
```
### Starting the Development Server
3. Start the development server for the frontend:
```
npm run dev
```
# Screenshots
https://github.com/Dheerajjha451/Meet_Your_Pet/assets/106474979/5f2c5405-6bd1-431b-af68-6cf737516664
## Project Goal
Meet Your Pet project aims to match dogs with their best caretakers, bridging the gap between pets at different adoption centers and people seeking different breeds of dogs. By allowing users to upload images of dogs, helps the user to know if the dog is good for them by knowing the breed of the dog and a small description about the features of the dog. If the dog is available at any adoption center, the platform also offers information about the adoption center to potential dog owners. Through this process, Meet Your Pet strives to facilitate meaningful connections between dogs in need of homes and individuals eager to provide them with care and companionship.
## Current Status and Future Plans
At present, the Meet Your Pet project is equipped to predict the breed of a dog based on uploaded images and provide a short description of the breed. However, our journey doesn't end here. Our aim to connect the users with the adoption centers is not yet fully implemented.We'll shortly implement it.Through these enhancements, we aim to make the adoption process seamless and efficient, ensuring that every dog finds a loving and caring home. Stay tuned for updates as we work towards this goal!
# Contributing
Check out the [contributing guidelines](https://github.com/Dheerajjha451/Meet_Your_Pet/blob/main/CONTRIBUTING.md)
# License
This project is licensed under the [License.](https://github.com/Dheerajjha451/Meet_Your_Pet/blob/main/LICENSE)
| Meet Your Pet is not just a web application, It's a bridge between loving homes and our furry friends waiting for their forever famillies. With the help of cutting edge technologies, our application offers a unique way to help a stray dog meet a heartwarming family. | flask,image-prediction,javascript,machine-learning,reactjs,tailwindcss,website | 2024-03-23T05:22:53Z | 2024-05-13T15:02:51Z | 2024-04-16T01:25:30Z | 2 | 0 | 56 | 1 | 0 | 3 | null | Apache-2.0 | Jupyter Notebook |
zahidrahimoon/Typescript | master | <h1 align="center">
TypeScript
<img align="center" src="https://img.icons8.com/color/48/000000/typescript.png" alt="TypeScript icon">
</h1>
1. **What is TypeScript, and how does it differ from JavaScript?**
- TypeScript is a statically typed superset of JavaScript that adds optional types to the language. This means you can define types for variables, function parameters, return values, and more in TypeScript, which helps catch errors early in the development process. JavaScript, on the other hand, is dynamically typed, meaning types are determined at runtime.
2. **How do you define a variable with a specific type in TypeScript?**
- In TypeScript, you can define a variable with a specific type using the syntax `variableName: type`. For example, `let age: number = 25;` defines a variable `age` of type `number` with the value `25`.
3. **What is meant by Type annotations in TypeScript?**
- Type annotations in TypeScript are a way to explicitly specify the type of a variable, function parameter, return value, or any other entity that requires a type. By using type annotations, you can define the expected types in your code, which helps TypeScript catch errors early and provides better documentation and understanding of the code.
```typescript
let name: string = "Zahid Rahimoon";
```
- Type annotations are optional in TypeScript, as TypeScript can often infer the types based on the value assigned. However, using explicit type annotations is considered good practice, especially for code clarity and error prevention.
4. **List of Type annotation in Typescript**
- Here are some type annotation in TypeScript:
1. ***Basic Types:***
```typescript
let age: number = 18;
let name: string = "Zahid";
let isValid: boolean = true;
```
2. ***Arrays:***
```typescript
let numbers: number[] = [1, 2, 3];
let names: string[] = ["Zahid", "Zara", "Rahimoon"];
let flags: boolean[] = [true, false, true];
```
3. ***Objects:***
```typescript
let user: { name: string, age: number } = { name: "Zara", age: 17 };
```
4. ***Intersection Types:***
```typescript
interface Person {
name: string;
age: number;
}
function greet(person: Person) {
return `Hello, ${person.name}!`;
}
let user = { name: "Zahid", age: 18 };
console.log(greet(user));
```
5. **What is a type alias in TypeScript?**
- A type alias in TypeScript allows you to create a new name for a type. It's similar to defining a new type but can be more descriptive and reusable.
6. **How do you declare a type alias in TypeScript?**
- To declare a type alias, you use the `type` keyword followed by the alias name and the type definition. For example:
```typescript
type MyString = string;
```
7. **What are the benefits of using type aliases?**
- Type aliases can improve code readability and maintainability by providing descriptive names for complex types. They also allow you to easily reuse types throughout your codebase.
8. **How do you create a type alias for an object type in TypeScript?**
- To create a type alias for an object type, you define the alias name and specify the object's properties along with their types. For example:
```typescript
type MyObject = { id: number; name: string };
```
9. **Can you use type aliases to define recursive types in TypeScript?**
- Yes, you can use type aliases to define recursive types by using the alias name within the type definition. However, you need to be careful to avoid infinite recursion.
10. **What is the difference between type aliases and interfaces in TypeScript?**
- Type aliases and interfaces are similar but have some differences. One key difference is that type aliases can represent any type, including primitive types, union types, and intersection types, while interfaces can only represent object types.
11. **When should you use a type alias instead of an interface in TypeScript?**
- Use a type alias when you need to create a name for a complex type that can't be expressed easily with an interface, such as union types, intersection types, or tuple types. Use an interface when you're defining the shape of an object type.
12. **Difference between function declarations and arrow functions:**
- Function declarations use the `function` keyword and have their own `this` context.
- Arrow functions use the `=>` syntax and do not have their own `this` context, instead, they inherit `this` from the surrounding code.
13. **`this` keyword in JavaScript and arrow functions:**
- In JavaScript, `this` refers to the current execution context. In arrow functions, `this` is lexically scoped and refers to the `this` value of the surrounding code.
14. **Higher-order functions example:**
- Higher-order functions are functions that take other functions as arguments or return functions. For example:
```typescript
function applyOperation(a: number, b: number, operation: (x: number, y: number) => number): number {
return operation(a, b);
}
const sum = (x: number, y: number) => x + y;
const result = applyOperation(5, 3, sum);
console.log(result); // Output: 8
```
15. **Defining optional parameters:**
- Optional parameters in TypeScript are denoted by adding a `?` after the parameter name.
```typescript
function greet(name?: string) {
if (name) {
console.log(`Hello, ${name}!`);
} else {
console.log("Hello, World!");
}
}
greet(); // Output: Hello, World!
greet("Zahid"); // Output: Hello, Zahid!
```
16. **Function overloading:**
- Function overloading allows a function to have multiple signatures. TypeScript will determine which function signature to use based on the number and types of arguments provided.
```typescript
function combine(a: string, b: string): string;
function combine(a: number, b: number): number;
function combine(a: any, b: any): any {
return a + b;
}
const result1 = combine("Hello, ", "world!");
const result2 = combine(5, 3);
```
17. **Difference between `foo(): void` and `foo(): undefined`:**
- `foo(): void` indicates that the function does not return a value, while `foo(): undefined` indicates that the function returns `undefined`.
Certainly! Let's go through the interview questions first, and then I'll provide five programs for each concept: arrays, tuples, and enums.
18. **How do you declare an array in TypeScript?**
- Answer: An array in TypeScript can be declared using the following syntax:
```typescript
let arrayName: dataType[] = [value1, value2, ...];
```
19. **What is the difference between declaring an array using `[]` and using the `Array` type?**
- Answer: Declaring an array using `[]` specifies the type of elements directly, while using the `Array` type allows you to specify the type of elements as a generic parameter.
20. **How can you access elements in an array?**
- Answer: Elements in an array can be accessed using index notation, e.g., `arrayName[index]`.
21. **How do you add elements to an array?**
- Answer: Elements can be added to an array using methods like `push()`, `unshift()`, or by directly assigning a value to a specific index.
22. **How do you remove elements from an array?**
- Answer: Elements can be removed from an array using methods like `pop()`, `shift()`, or by using the `splice()` method.
23. **Explain the difference between `forEach`, `map`, `filter`, and `reduce` methods when working with arrays.**
- Answer:
- `forEach`: Iterates over each element in the array and executes a callback function.
- `map`: Creates a new array by applying a function to each element in the array.
- `filter`: Creates a new array with elements that pass the test of a provided function.
- `reduce`: Reduces the array to a single value by applying a function to each element and accumulating the result.
24. **What is a tuple in TypeScript?**
- Answer: A tuple is a data structure in TypeScript that allows you to store a fixed number of elements of different types.
25. **How do you declare a tuple?**
- Answer: Tuples are declared using square brackets `[]` with the types of elements inside, e.g., `[type1, type2, ...]`.
26. **How is a tuple different from an array?**
- Answer: Tuples have a fixed number of elements with known types, while arrays can have a variable number of elements of the same type.
27. **Can the order of types in a tuple be changed?**
- Answer: No, the order of types in a tuple cannot be changed after it is declared.
28. **How do you access elements in a tuple?**
- Answer: Elements in a tuple can be accessed using index notation, similar to arrays, e.g., `tupleName[index]`.
29. **Can a tuple contain elements of different data types?**
- Answer: Yes, a tuple can contain elements of different data types.
30. **What is an enum in TypeScript?**
- Answer: An enum in TypeScript is a way to define a set of named constants.
31. **How do you declare an enum?**
- Answer: Enums are declared using the `enum` keyword, followed by the enum name and a list of constant values.
32. **Can enums have string values?**
- Answer: Yes, enums can have string values by explicitly assigning values to each enum member..
33. **How do you access enum values?**
- Answer: Enum values can be accessed using dot notation, e.g., `EnumName.EnumMember`.
34. **Can you assign a numeric value to enum members?**
- Answer: Yes, enum members can be assigned numeric values, which can be useful for creating mappings or calculations.
35. **How are enums different from objects?**
- Answer: Enums are similar to objects in that they can have properties, but enums are limited to a set of predefined values and cannot have methods or additional properties.
| Practice and Interview questions | front-end-development,frontend,javascript,tyepscript,webdevelopment | 2024-04-12T15:03:17Z | 2024-05-12T04:50:01Z | null | 1 | 0 | 46 | 0 | 0 | 3 | null | null | JavaScript |
OpenSourceTreasure/No-Distraction-Dark-Mode-HTML-Webpage | main | # No-Distraction-Dark-Mode-HTML-Webpage
Sometimes you just need a blank webpage to look at so you can think and chill out in between projects. The HTML page, Title and Favicon are all in dark mode.
There are two parts to this:
✅ HTML Webpage
✅ Favicon
The HTML Webpage uses simple code to create a "dark mode" page. It points to a black colored Favicon, so the tab will be in dark mode as well. The HTML title, which appears on the browser tab, is also blank, with the following code:
```HTML
<title></title>
```
How to setup:
1️⃣ Decide where you will store the two files (HTML and Favicon). I recommend My Documents.
2️⃣ Change the below code in the HTML file to reflect the directory where you will store the Favicon:
```HTML
<link rel="shortcut icon" type="image/x-icon" href="/Users/name/Documents/favicon.ico">
```
3️⃣ Put the HTML file in the same directory as the Favicon.
4️⃣ Rename the HTML file as you wish.
5️⃣ In your browser, set the Homepage to the HTML file that you renamed.
6️⃣ Make sure your browser is set to display the homepage icon.
7️⃣ Click the homepage icon and enjoy a few moments of quiet thinking..
Here is the HTML if you want to copy and paste it:
```HTML
<html>
<link rel="shortcut icon" type="image/x-icon" href="/Users/name/Documents/favicon.ico">
<head><title></title></head>
<body bgcolor="black">
</body>
</html>
```
🌟 In this version, the favicon image is embedded in the HTML via Base64. The filename is No Distraction Webpage - Base64 Favicon.html. The code is below:
```HTML
<html>
<head>
<link rel="shortcut icon" href="data:image/png;base64,AAABAAEAEBACAAEAAQCwAAAAFgAAACgAAAAQAAAAIAAAAAEAAQAAAAAAgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA////AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD//wAA//8AAP//AAD//wAA//8AAP//AAD//wAA//8AAP//AAD//wAA//8AAP//AAD//wAA//8AAP//AAD//wAA">
<title></title>
</head>
<body bgcolor="black">
</body>
</html>
```
Relaxing Countdown Timer
In this version, you decide how long you want to see the blank page and relax. End the session by clicking stop on the bottom. Below is the code. The filename is "Home Time.html".
```HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title></title>
<style>
@import url('https://fonts.googleapis.com/css2?family=Lato:wght@300;400&display=swap');
body {
background-color: black;
color: white;
font-family: 'Lato', sans-serif;
text-align: center;
position: relative;
height: 100vh;
margin: 0;
transition: all 0.3s ease-in-out;
}
#header {
font-size: 24px;
margin-top: 1em;
}
#customTime {
font-family: 'Lato', sans-serif;
padding: 10px;
border: 1px solid white;
background-color: transparent;
color: white;
margin-top: 1em;
}
#startButton, #stopButton {
background-color: transparent;
color: white;
border: none;
cursor: pointer;
padding: 10px 20px;
font-size: 16px;
}
#inputSection {
display: block;
margin-top: 1em;
}
#countdownSection, #stopButton {
display: none; /* Hide by default */
}
#stopButton {
position: absolute;
right: 20px;
bottom: 20px;
}
#feedback {
color: red;
margin-top: 10px;
display: none; /* Hide by default, shown on invalid input */
}
</style>
<link rel="shortcut icon" type="image/x-icon" href="/Users/name/Documents/favicon.ico">
</head>
<body>
<div id="header">It's time to relax...</div>
<br> <!-- Line break added here -->
<div id="inputSection">
<input type="number" id="customTime" placeholder="Enter relaxation time">
<button id="startButton" onclick="startCountdown()">Start</button>
<div id="feedback"></div>
</div>
<div id="countdownSection">
<!-- Countdown display goes here -->
</div>
<button id="stopButton" onclick="stopCountdown()">Stop</button>
<script>
const countdownSection = document.getElementById("countdownSection");
const customTimeInput = document.getElementById("customTime");
const inputSection = document.getElementById("inputSection");
const stopButton = document.getElementById("stopButton");
const feedback = document.getElementById('feedback');
let intervalId = null;
function startCountdown() {
const relaxationTimeMinutes = parseInt(customTimeInput.value, 10);
if (isNaN(relaxationTimeMinutes) || relaxationTimeMinutes <= 0) {
feedback.textContent = "Please enter a valid time in minutes.";
feedback.style.display = 'block';
return;
} else {
feedback.style.display = 'none';
}
inputSection.style.display = 'none';
countdownSection.style.display = 'block';
stopButton.style.display = 'block';
const endTime = Date.now() + relaxationTimeMinutes * 60 * 1000;
function updateCountdown() {
const currentTime = Date.now();
const remainingTime = endTime - currentTime;
if (remainingTime <= 0) {
countdownSection.textContent = "Time's up!";
clearInterval(intervalId);
stopCountdown();
return;
}
const minutes = Math.floor(remainingTime / 60000);
const seconds = Math.floor((remainingTime % 60000) / 1000);
countdownSection.textContent = `Time remaining: ${minutes} min ${seconds} sec`;
}
updateCountdown();
intervalId = setInterval(updateCountdown, 1000);
}
function stopCountdown() {
clearInterval(intervalId);
countdownSection.style.display = 'none';
stopButton.style.display = 'none';
inputSection.style.display = 'block';
customTimeInput.value = '';
}
</script>
</body>
</html>
```
⭐ Bonus Section ⭐
1️⃣ Redirect to HTML pages based on time of day
Someone may want two sets of links - one for day (work related) and one for night.
In the below, you create two additional webpages - index-day.html and index-night.html. The code is currently
set to redirect to index-day.html between 6am and 7pm (the 6 and 19 variables). No special code needed for the day and night index pages. Change the links
as you wish (perhaps to even non-HTML links). A downloadable HTML file of the below is available.
```HTML
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Links</title>
</head>
<body>
<script type="text/javascript">
// var SpecialRedirectURL = ['night.html','morning.html','day.html','eve.html'];
var SpecialRedirectURL = [
'index-night.html',
'index-day.html'
];
function specRedirect() {
var currentTime = new Date();
var currentHour = currentTime.getHours();
var Hour = 0;
if ( (currentHour >= 6) && (currentHour < 19) ) { Hour = 1; }
// alert(Hour+' goes to: '+SpecialRedirectURL[Hour]);
window.location.href = SpecialRedirectURL[Hour];
}
window.onload = function() {
specRedirect();
}
</script>
</body>
</html>
```
2️⃣ A dark mode wallpaper image for your smartphone
Skip the busy wallpaper photo that your apps are covering and go for simplicity! I created an image that is what I believe to be the largest commonly used resolution for smartphones - 3200 x 1440. It should resize perfectly for any smaller resolution as there are no pixels in it - just dark mode black. The below image can be downloaded as well. Rotate it if you need.
Ideas for forks..
💡 Change the colors
💡 Add minimalist content like the weather
💡 Have the "time of day" webpage load applications based on time and even if-then statements
💡 Whatever else you can think of
Enjoy!
| No distraction, dark mode, HTML webpage so you can chill out in between projects | dark-mode,distraction-free,favicon,homepage,html,relax,webpage,background-image,wallpaper,javascript | 2024-04-30T00:06:41Z | 2024-05-22T10:01:10Z | null | 1 | 0 | 78 | 0 | 0 | 3 | null | null | HTML |