Javascript Guide: Advanced JS
Tags: javascript, programming, webdev, beginners
Published: 2023-01-25 12:22:43

> 👉 If you are new to JavaScript, I recommend starting with my blog on the "[basics of JavaScript](https://dev.to/anujnegi_/javascript-guide-basics-of-js-39ma)" before diving into this one on advanced topics.

Welcome 🙏 to my new blog on **Advanced JavaScript**! In this blog, we will dive deep into the language's intricacies, covering topics such as prototype-based inheritance, object-oriented programming, asynchronous JavaScript, and more. Whether you're a beginner looking to take your skills to the next level or a seasoned developer looking to brush up on the latest features, this series has something for you. So let's get started and take your JavaScript knowledge to the next level!

### 1\. Understanding JavaScript's prototype-based inheritance and how to use it.

JavaScript's prototype-based inheritance is a key feature that allows developers to create objects that inherit properties and methods from other objects. This is different from a class-based inheritance, which is commonly found in other programming languages.

To understand prototype-based inheritance, it's important to understand the concept of prototypes in JavaScript. Every object in JavaScript has a prototype, which is another object that can inherit properties and methods. By default, the prototype of an object is set to the built-in `Object.prototype`.

To create a new object that inherits from another object, we can use the `Object.create()` method. For example, let's say we have an object called "Person" with properties such as "name" and "age". We can create a new object called "Student" that inherits from "Person" like this:

```javascript
let Person = {
  name: "John Doe",
  age: 25
};

let Student = Object.create(Person);
Student.major = "Computer Science";
console.log(Student.name); // "John Doe"
console.log(Student.major); // "Computer Science"
```

In this example, we use `Object.create()` to create a new object "Student" that inherits from "Person". We can then add additional properties, such as "major", to the "Student" object without affecting the "Person" object.

It's also possible to override properties from the prototype by simply reassigning them to the new object. For example, let's say we want to change the name of the student:

```javascript
Student.name = "Jane Smith";
console.log(Student.name); // "Jane Smith"
console.log(Person.name); // "John Doe"
```

As you can see prototype-based inheritance is a powerful feature in JavaScript, allowing for efficient object creation and easy property reuse. It is an essential concept for understanding the language and writing effective code.

### 2\. Advanced concepts of JavaScript's object-oriented programming(ES6 classes).

JavaScript's object-oriented programming (OOP) features allow you to create complex and modular code. One of the most important concepts in OOP is the class. Classes in JavaScript are a way of creating objects that have similar characteristics and behavior. With the introduction of ES6, JavaScript classes have become more powerful and easy to use.

Here's an example of a simple class in JavaScript:

```javascript
class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  sayHello() {
    console.log(`Hello, my name is ${this.name} and I am ${this.age} years old`);
  }
}

const john = new Person("John", 25);
john.sayHello(); // Outputs "Hello, my name is John and I am 25 years old"
```

In this example, we have a `Person` class with a constructor function that takes two arguments, `name` and `age`, and assigns them to the object's properties. We also have a method called `sayHello` that logs a string to the console. We create an instance of the class using the `new` keyword and call the method on it.

Classes also support inheritance, which allows you to create a new class that inherits the properties and methods of an existing class. Here's an example:

```javascript
class Student extends Person {
  constructor(name, age, major) {
    super(name, age);
    this.major = major;
  }

  sayHello() {
    console.log(`Hello, my name is ${this.name}, I am ${this.age} years old, and my major is ${this.major}`);
  }
}

const jane = new Student("Jane", 22, "Computer Science");
jane.sayHello(); // Outputs "Hello, my name is Jane, I am 22 years old, and my major is Computer Science"
```

In this example, we create a `Student` class that inherits from the `Person` class. We added a new property `major` and we override the `sayHello` method to include it in the output.

ES6 classes make it easy to create and manage objects with similar characteristics and behavior, and they also make it easy to create a hierarchy of classes that can share common functionality. This is a powerful feature that allows you to create more maintainable and scalable code.

### 3\. Asynchronous JavaScript: Understanding callbacks, promises, and async/await.

Asynchronous JavaScript is one of the key features of the language that allows you to perform multiple tasks simultaneously without blocking the execution of your code. In this post, we'll take a closer look at three of the most important techniques for working with asynchronous JavaScript: **callbacks**, **promises**, and **async/await**.

First, let's start with **callbacks**. A callback is a function that is passed as an argument to another function and is executed after the first function has been completed. Callbacks are often used to handle the results of asynchronous operations, such as loading data from a server.

For example, let's say we want to load a JSON file from a server using the `fetch` function. We can pass a callback function as an argument to the `fetch` function, which will be called when the data has been loaded:

```javascript
fetch('data.json')
    .then(response => response.json())
    .then(data => {
        // do something with the data
    });
```

Next, let's take a look at **promises**. A promise is an object that represents the eventual completion or failure of an asynchronous operation. It provides a more powerful and flexible way to handle async operations compared to callbacks.

For example, let's say we want to load a JSON file from a server using the `fetch` function and return a promise:

```javascript
function loadJSON(url) {
    return fetch(url)
        .then(response => response.json())
}

loadJSON('data.json')
    .then(data => {
        // do something with the data
    });
```

Finally, let's take a look at **async/await**. The async/await syntax is a more recent addition to JavaScript and it allows you to write asynchronous code in a way that looks and behaves like synchronous code.

For example, let's say we want to load a JSON file from a server using the `fetch` function and using async/await:

```javascript
async function loadJSON(url) {
    const response = await fetch(url);
    const data = await response.json();
    // do something with the data
}

loadJSON('data.json');
```

As you can see, with each technique, we achieve the same result with different syntax and semantics. Understanding when and how to use callbacks, promises, and async/await is crucial for writing efficient and maintainable asynchronous JavaScript code.

These are just a few examples of how you can work with asynchronous JavaScript, and there's much more to explore. Asynchronous JavaScript is a powerful and versatile feature of the language that can help you create fast, responsive, and concurrent applications.

### 4\. Working with web APIs: Fetch API and XmlHttpRequest.

Working with web APIs is a crucial aspect of modern web development and JavaScript provides several ways to interact with them. Two popular options are the **Fetch API** and **XmlHttpRequest**.

**Fetch API** is a modern, promise-based API that allows you to make HTTP requests to a server. It is built into most modern browsers and is considered a replacement for XmlHttpRequest. Here's an example of how you can use the Fetch API to retrieve data from an API endpoint:

```javascript
fetch('https://jsonplaceholder.typicode.com/todos/1')
  .then(response => response.json())
  .then(data => console.log(data))
```

**XmlHttpRequest**, commonly referred to as XHR, is a legacy API that has been around since the early days of web development. It allows you to make HTTP requests to a server and receive responses. Here's an example of how you can use XmlHttpRequest to retrieve data from an API endpoint:

```javascript
var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://jsonplaceholder.typicode.com/todos/1');
xhr.onload = function() {
  if (xhr.status === 200) {
    console.log(xhr.responseText);
  }
};
xhr.send();
```

Both the Fetch API and XmlHttpRequest provide different ways to make HTTP requests, but the Fetch API is considered more modern and recommended for use. By mastering these web API request methods, you can take your JavaScript skills to the next level and build exciting and interactive web applications.

### 5\. Advanced DOM manipulation: Creating custom elements, Web Components, and shadow DOM.

One of the most exciting features of JavaScript is the ability to manipulate the Document Object Model (DOM) in real-time, giving you the power to create dynamic and interactive web pages. One of the most powerful ways to do this is by creating **custom elements**, **web components**, and **shadow DOM**.

**Custom elements** are a way to create new HTML tags that can be used on web pages. With custom elements, you can define your element and give it custom properties and methods. For example, you can create a custom element that displays a countdown timer, and use it in your HTML like this:

```javascript
<countdown-timer end-time="2022-12-31"></countdown-timer>
```

**Web components**, on the other hand, are a collection of technologies that allows you to create reusable custom elements with their behavior and styles. They allow you to create components that can be easily shared and reused across your website or even across different websites. For example, you can create a web component that displays a set of cards with different images and text and use it in your HTML like this:

```javascript
<card-deck>
  <card-element image="image1.jpg" title="Card 1"></card-element>
  <card-element image="image2.jpg" title="Card 2"></card-element>
  <card-element image="image3.jpg" title="Card 3"></card-element>
</card-deck>
```

Finally, **Shadow DOM** is a way to encapsulate the styles and behavior of a web component, so that it can be used without affecting the rest of the page. It's like a private DOM that's only accessible to the web component it belongs to. This makes it easy to keep the styles and behavior of a web component separate from the rest of the page, which makes it more predictable and easier to debug.

Creating custom elements, web components, and shadow DOM allows you to create powerful and reusable components that can be easily shared and reused across your website. It's a great way to add interactivity and dynamic content to your web pages and is a must-know for any JavaScript developer.

### 6\. JavaScript's event loop and how it works.

One of the most powerful and exciting features of JavaScript is its **event loop**. The event loop is a mechanism that allows JavaScript to handle asynchronous code execution, allowing the language to handle multiple tasks at the same time.

The event loop works by placing any asynchronous code, such as setTimeout or XHR requests, into a queue. The JavaScript engine then processes the items in the queue in the order they were added, allowing for non-blocking code execution.

For example, consider the following code:

```javascript
console.log("Start");
setTimeout(() => console.log("Timeout"), 2000);
console.log("End");
```

The output will be: "Start", "End", "Timeout"

The setTimeout function is placed in the queue and will only be processed after the synchronous code has been executed.

This mechanism is what allows JavaScript to handle multiple tasks at the same time and can lead to more responsive and performant code.

It's important to note that, the event loop is not unique to JavaScript, other programming languages like Python, Ruby, and C# also have their event loop mechanism to handle the concurrency.

In conclusion, the event loop is a powerful feature of JavaScript that enables the language to handle asynchronous code execution, improving performance and responsiveness. Understanding how the event-loop works are essential for mastering JavaScript and building efficient, high-performance applications.

### 7\. Advanced debugging and troubleshooting techniques.

**Debugging and troubleshooting** are critical skills for any developer, and JavaScript is no exception. In this blog post, we will explore some advanced techniques for debugging and troubleshooting JavaScript code.

First, let's talk about the **browser's developer tools**. Most modern web browsers come with built-in developer tools that can be used to debug JavaScript code. These tools allow you to see the values of **variables**, set **breakpoints**, and step through your code line by line. This is an essential tool for debugging JavaScript and should be the first place you look when trying to troubleshoot an issue.

Another important technique is the use of **console.log()** statements. These statements can be placed throughout your code to output the values of variables, functions, or any other data you want to inspect. This can be especially useful when working with asynchronous code, as you can use console.log() statements to see the order in which your code is executing.

Another advanced technique is the use of **JavaScript profilers**. Profilers allow you to see where your code is spending the most time and identify performance bottlenecks. This can be incredibly useful when trying to optimize your code for performance.

Finally, it's important to have a solid understanding of JavaScript's event loop and how it works. This will help you understand how your code is executing, and how different pieces of your code are interacting with each other.

By using these advanced debugging and troubleshooting techniques, you will be able to quickly identify and fix issues in your JavaScript code, making you a more effective and efficient developer.

### 8\. JavaScript Design Patterns: Module, Factory, Observer, etc.

JavaScript design patterns are reusable solutions to commonly occurring problems in code. One of the most popular design patterns in JavaScript is the **"module"** pattern, which allows you to encapsulate and organize your code in a way that is both maintainable and easy to understand. The module pattern is implemented using **closures** and **immediately-invoked function expressions (IIFEs)**.

Here is an example of the module pattern in action:

```javascript
const myModule = (function() {
  let privateVariable = "Hello";
  function privateMethod() {
    console.log(privateVariable);
  }
  return {
    publicMethod: function() {
      privateMethod();
    }
  };
})();

myModule.publicMethod(); // Outputs "Hello"
```

Another popular pattern is the **"factory"** pattern, which allows you to create objects with a similar interface, but with different implementations. This is useful when you want to create similar objects with different properties or methods.

Here is an example of the factory pattern in action:

```javascript
function createPerson(name, age) {
  return {
    name,
    age
  };
}

const person1 = createPerson("John", 30);
const person2 = createPerson("Jane", 25);
console.log(person1); // {name: "John", age: 30}
console.log(person2); // {name: "Jane", age: 25}
```

The **"observer"** pattern is a behavioral pattern that allows objects to subscribe to and receive notifications from other objects. This pattern is often used in event-driven systems.

Here is an example of the observer pattern in action:

```javascript
class Subject {
  constructor() {
    this.observers = [];
  }
  subscribe(observer) {
    this.observers.push(observer);
  }
  unsubscribe(observer) {
    this.observers = this.observers.filter(obs => obs !== observer);
  }
  fire(action) {
    this.observers.forEach(observer => {
      observer.update(action);
    });
  }
}

class Observer {
  constructor(state) {
    this.state = state;
    this.initialState = state;
  }
  update(action) {
    switch (action.type) {
      case "INCREMENT":
        this.state = ++this.state;
        break;
      case "DECREMENT":
        this.state = --this.state;
        break;
      default:
        this.state = this.initialState;
    }
  }
}

const stream$ = new Subject();
const obs1 = new Observer(1);
const obs2 = new Observer(42);

stream$.subscribe(obs1);
stream$.subscribe(obs2);
stream$.fire({ type: "INCREMENT" });
console.log(obs1.state); // 2
console.log(obs2.state); // 43
```

These design patterns are just a few examples of the many powerful techniques available to JavaScript developers. By understanding and applying these patterns, you can write more maintainable and scalable code.

Please let me know if you would like any further information on this topic.

### 9\. Working with JavaScript libraries and frameworks such as React, Angular, Vue, etc.

JavaScript libraries and frameworks are powerful tools for building complex and dynamic web applications. They provide a set of pre-built components and functionality that can save you time and effort when building your projects. Some of the most popular JavaScript libraries and frameworks such as **React**, **Angular**, and **Vue**.

**React** is a JavaScript library for building user interfaces. It is often used for building large and complex web applications. React's main strength is its ability to efficiently update the user interface based on changes to the underlying data.

**Angular** is a framework for building web applications. It provides a set of tools for creating reusable components and managing the application state. Angular is often used for building large and complex web applications with a lot of data binding.

**Vue** is a JavaScript framework for building user interfaces. It is similar to React and Angular in that it allows for building complex web applications. Vue's main strength is its ability to quickly update the user interface based on changes to the underlying data.

Each of these libraries and frameworks has its unique features and benefits, and choosing the right one for your project will depend on the specific requirements of your application. However, all of them can help you to create web applications that are fast, responsive, and easy to maintain.

### 10\. Tips and best practices for optimizing JavaScript performance and scalability.

Optimizing JavaScript performance and scalability is crucial for creating fast and efficient web applications. Here are a few tips and best practices to help you do just that:

1. **Use the latest version of JavaScript**: JavaScript is constantly evolving, and newer versions often bring performance improvements. Make sure you're using the latest version of the language, and consider using a transpiler to convert your code to an older version for better browser compatibility.
    
2. **Minimize the number of DOM operations**: The Document Object Model (DOM) is a slow and resource-intensive aspect of web development. Minimize the number of operations you perform on the DOM to improve performance.
    
3. **Use a build tool**: Tools like Webpack and Babel can help you reduce the size of your code and improve performance by minifying and transpile your code.
    
4. **Use a Content Delivery Network (CDN)**: CDNs are a great way to speed up your website by delivering your resources to the user from a server that is geographically closer to them.
    
5. **Use a Performance monitoring tool**: Performance monitoring tools like Lighthouse and Google Analytics give you insights into how your website is performing and can help you identify and fix performance bottlenecks.
    
6. **Avoid using global variables**: Global variables are a potential source of conflicts and bugs, and can slow down your application. Instead, use a module pattern or an ES6 module system for encapsulation.
    
7. **Use caching**: Caching allows you to store the results of expensive operations and reuse them later, which can significantly improve performance.
    
8. **Be mindful of memory usage**: Memory leaks can cause performance issues. Be mindful of how you're using memory in your application and use a tool like the Chrome DevTools to identify and fix memory leaks.
    

By following these tips and best practices, you can improve the performance and scalability of your JavaScript applications and create a better user experience.

### Conclusion

In conclusion, advanced JavaScript is a vast and powerful subject that can take your coding skills to the next level. From understanding the intricacies of prototype-based inheritance to working with web APIs, asynchronous JavaScript, and more, there's a wealth of knowledge to be gained from exploring the advanced features of this versatile programming language. I've covered a lot of ground in this blog post, from best practices for optimizing JavaScript performance and scalability to understanding the event loop, working with web APIs, and more. I hope that this blog post has been informative and helpful in your journey to becoming an advanced JavaScript developer. As always, practice makes perfect, so keep experimenting with these concepts, and don't be afraid to dig deeper into the topics that interest you the most. Happy coding! 💛😊