React.js has become the go-to library for building dynamic user interfaces on the web. With its vast popularity comes a high demand for skilled React developers. If you’re preparing for a React.js interview, this blog post is your one-stop guide!

We’ve compiled the top 20 React.js interview questions you’re likely to encounter, along with clear and concise answers to help you showcase your knowledge and understanding.

Let’s get started!

1.  Differentiate between Real DOM and Virtual DOM.

Ans :

Real DOM	Virtual  DOM
1. It updates slowly.	1. It updates faster.
2. Can directly update HTML.	2. Can’t directly update HTML.
3. Creates a new DOM if element updates.	3. Updates the JSX if element updates.
4. DOM manipulation is very expensive.	4. DOM manipulation is very easy.
5. Too much memory wastage.	5. No memory wastage.

2. What is React?

• React is a front-end JavaScript library developed by Facebook in 2011.
• It follows the component based approach which helps in building reusable UI components.
• It is used for developing complex and interactive web and mobile UI.
• Even though it was open-sourced only in 2015, it has one of the largest communities supporting it.

3. What are the features of React?

Ans. Major features of React are listed below:

1. It uses the virtual DOM instead of the real DOM.
2. It uses server-side rendering.
3. It follows uni-directional data flow or data binding.

4. List some of the major advantages of React.

Ans: Some of the major advantages of React are:

1. It increases the application’s performance
2. It can be conveniently used on the client as well as server side
3. Because of JSX, code’s readability increases
4. React is easy to integrate with other frameworks like Meteor, Angular, etc
5. Using React, writing UI test cases become extremely easy.

5. What are the limitations of React?

Ans: Limitations of React are listed below:

1. React is just a library, not a full-blown framework
2. Its library is very large and takes time to understand
3. It can be little difficult for the novice programmers to understand
4. Coding gets complex as it uses inline templating and JSX

6. What is JSX?

Ans: JSX is a shorthand for JavaScript XML. This is a type of file used by React which utilizes the expressiveness of JavaScript along with HTML like template syntax. This makes the HTML file really easy to understand. This file makes applications robust and boosts its performance.

7. What do you understand by Virtual DOM? Explain its works.

Ans: A virtual DOM is a lightweight JavaScript object which originally is just a copy of the real DOM. It is a node tree that lists the elements, their attributes and content as Objects and their properties. React’s render function creates a node tree out of the React components. It then updates this tree in response to the mutations in the data model which is caused by various actions done by the user or by the system. Check out this Full stack developer course online to learn more about react.

8. Why can’t browsers read JSX?

Ans: Browsers can only read JavaScript objects but JSX in not a regular JavaScript object. Thus to enable a browser to read JSX, first, we need to transform JSX file into a JavaScript object using JSX transformers like Babel and then pass it to the browser.

9. How is React different from Angular?

Ans:

TOPIC	REACT	ANGULAR
1. ARCHITECTURE	Only the View of MVC	Complete MVC
2. RENDERING	Server-side rendering	Client-side rendering
3. DOM	Uses virtual DOM	Uses real DOM
4. DATA BINDING	One-way data binding	Two-way data binding
5. DEBUGGING	Compile time debugging	Runtime debugging
6. AUTHOR	Facebook	Google

10. “In React, everything is a component.” Explain.

Ans: Components are the building blocks of a React application’s UI. These components split up the entire UI into small independent and reusable pieces. Then it renders each of these components independent of each other without affecting the rest of the UI.

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