React JS Interview Questions and Answers

React JS is most popular JavaScript libraries now a days because its simple and declarative API produces highly-performant applications. If you are planing to build a robust web application, React JS can be best suit JavaScript libraries for UI development. and you are React JS developer, here we are providing mostly asked questions in interview.


What is React JS?

React JS is a front end JavaScript library for creating UI, it is developed by Facebook in 2011. It is a component based approach to create reusable UI components. It can be used for developing complex and interactive web and mobile UI.


What are the features of React?

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.


What are the advantages of using ReactJS and how it’s different from other JavaScript Frameworks? What are its limitations?

Advantages of ReactJS:

React uses virtual DOM which is JavaScript object. This improves application performance as JavaScript virtual DOM is faster than the regular DOM.

  • It increases the application’s performance
  • It can be easily used on the client as well as server side
  • Because of JSX, code’s readability increases
  • React is easy to integrate with other frameworks like Angular, etc
  • Using React, writing UI test cases become easy

Limitations of ReactJS:

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


What are Components in ReactJS? Explain the Component Lifecycle.

  • getDefaultProps and getInitialState, both methods are called only once while initially rendering of the component.
  • componentWillMount : This method is executed just before rendering on both client and server side.
  • ComponentDidMount: This method is executed after first rendering only on the client side. This is where AJAX requests and DOM or state updates usually occurs. This method is also used for integration with other JavaScript frameworks.
  • ComponentWillReceiveProps: This method is invoked as soon as the props are updated before another render is called.
  • ShouldComponentUpdate: This method  should return true or false value. This  determines whether if a component will be updated or not. Default it is set to true.
  • ComponentWillUpdate: This method  is called just before rendering.
  • ComponentDidUpdate: This method is called just after rendering.
  • ComponentWillUnmount: This method is called after the component is unmounted from the DOM.

Stateless and Stateful components

Stateless: When a component is “stateless”, it calculates state is calculated internally but it directly  never mutates it. With the same inputs, it will always produce the same output. It means it has no knowledge of the past, current or future state changes

Stateful : When a component is “stateful”, it is a central point that stores every information in memory about the app/component’s state, do has the ability to change it. It has knowledge of past, current and potential future state changes.
Stateful component  change the state, using this.setState method.


What is current stable version of React JS? 

Version: 15.5
Release on: April 7, 2017


What is JSX?

JSX is a short form of JavaScript XML. This is a type of file used by React which utilizes of JavaScript along with HTML like template syntax. This makes the HTML file really easy to understand. it  makes yours applications robust and boosts  Below is an example of JSX:


            <h1> Title from !!</h1>

What are the life Cycle of ReactJS??

  1. Initialization
  2. State/Property Updates
  3. Destruction


we will come with some more interview questions and answers on React JS

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