Top 10 React JS Interview Theory Questions and Answers 🌟🔥
Tags: webdev, javascript, react, career
Published: 2024-01-21 02:30:00

### 🚀 Let's Get Started 
To successfully pass interviews it is essential to grasp the ideas and importantly, thoroughly prepare for commonly asked questions.

It's crucial to have a solid understanding of the library's principles to advance your career as a Front-End or Full-Stack Developer.

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### 😭 Why THEORY ⁉️
I understand learning theory portion is not what every developer likes.

But, this showcases that you are confident in delivering your applications and provides you with a sense of superiority.

Also, for understanding complex practical questions, a strong foundation of theory is needed.

It will enable you to express ideas demonstrate your expertise and ensure success, in the interviews.

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### 1. **What is React?**

React.js is a front-end library developed by Meta (formerly Facebook) to build interactive elements on websites.

It follows the component-based approach which helps in building reusable UI interfaces.

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### 2. **What are the main features of React?**

React uses a Virtual DOM to improve efficiency.

It uses reusable UI components to develop user interfaces.

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### 3. **What are the advantages of React?**

- It is easy to learn and use
- Excellent cross-platform support
- Provides amazing developer tools
- UI-focused designs
- Because of JSX, the code’s readability increases

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### 4. **What are the limitations of React?**

React is just a library; it is not a complete framework.

We might need to add additional packages to extend the functionality.

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### 5. **What is JSX?**

JSX is an acronym that stands for JavaScript XML.

JSX is a syntax extension to JavaScript that allows writing JavaScript code that looks similar to HTML.

It is used in React to describe what the UI should look like.

By using JSX, we can write HTML structures in the same file that contains JavaScript code.

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### 6. **What are events in React.js?**

An event is an action that triggers as a result of the user action or system-generated event like a mouse click, loading of a web page, pressing a key, window resizes, etc.

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### 7. **Why is there a need for using keys in lists?**

A key is a unique identifier and it is used to identify which items have changed, been updated or deleted from the lists.

It also helps to determine which components need to be re-rendered instead of re-rendering all the components every time; therefore increasing performance

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### 8. **Do browsers understand JSX code?**

No, browsers can't understand JSX code.

It would be best if you had a transpiler to convert your JSX to regular JavaScript browsers.

The most widely used transpiler right now is Babel.

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### 9. **What is prop drilling?**

Prop Drilling is an anti-pattern in React.

It happens when you pass data from one component to many deeply nested children components.

The solution for getting rid of props drilling is to use React Context API or Redux.

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### 10. **How many elements can a valid React component return?**

A valid React component can return only one element.

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### 🌟 Wrapping Up
To put it simply, having a grasp of the theory portion of React.js guarantees a sense of confidence and knowledge ultimately setting the stage for achievement.