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Top 15 React Js Interview Questions 2020

by Priyanka Arora, May 17, 2020, 1053 Views, 1
Learning about React Js Interview Questions would only challenge your skillset and help to improve more. React Js is among the most in-demand technology in 2020 and still perceived to be growing in a couple of years. Mastering react js also pave out the path for react native which introduces application development as well. So, we will look at the top 15 such questions so let’s get started.

1.Explain the concept of Virtual DOM in React js

This is among the most asked react as interview question. render() in react js creates a blueprint of every object and updates every jsx element which is pretty faster as we are not dealing with dom directly. Then, changes are compared with the dom and updation process takes place on the dom with only changed nodes than checking the changes in dom and updating every single node that used to happen otherwise.

2. What is Redux?

Redux is also a js library used with react to write applications on either client side, server end to test the application better, and works in a unidirectional way like react.

3. What is next js?

React js is a library whereas next js is react js framework used to build server-side rendered application providing control over babel and webpack.

4.Explain Server Side Rendering in React Js

In client-side rendering, HTML gets loaded first, and then the content is drawn using js and API hits from the server whereas in server-side rendering, the components are loaded at server-side and the output is HTML code.

5.Explain render()

React apps call once ReactDom.render() where the root element is loaded into the dom And doesn’t modifies the container node but only the children nodes. Below index.js calls app.js which has our landing page component attached to it.

Top 15 React Js Interview Questions 2020

6. What do you understand by props and state in react js

State are variables that can be accessed only inside the component whereas props are parameters that are passed into components so that the same components can be reused with different parameters.

class AppComponent extends React.component{
 constructor(props) {

    this.state = {value: ''}
      return <input type="text" value={this.state.value}>Enter Name
class AppComponent extends React.component{
    return <div>Hello {}</div>
// passing the props
<AppComponent name='Priyanka' />
<AppComponent name='Arora' />

7. What is Flux?

Flux is an architecture that Facebook follows while developing react application for the unidirectional flow of data that react js uses via using dispatcher library along with NodeJs EventEmitter.

8. Have you heard about Jest?

Jest is a  module that is used to test react js applications.

yarn add –dev react-test-renderer

9.Explain one-way binding in react js

Unlike Angular which supports two-way data binding, in react js the state is passed onto the view where changes are reflected. There is one single source truth to it. What it means is that the container holding the value of object can only be changed/added/rendered from the component and its value would be reflected everywhere, unlike in Angular that you could change the value of object from both view and controller.

10. How would you implement loop in jsx?

render: function() {
  const elements = ['one', 'two', 'three'];
  return (
      {, index) => {
        return <li key={index}>{value}</li>

11. Do you know what is shadow dom?

Shadow dom are the implementation of elements you hide. Root is detached from children which can be accessed publically, but not the root.

var div = document.createElement('div');
var shadowRoot = div.attachShadow({mode: 'open'});
shadowRoot.innerHTML = '<h1>Hello Shadow DOM</h1>';


12. What are 3 limitations you see in react js

The reason to choose react js is that its faster, but now angular applications with new features have outdrawn that also. Angular has two-way data binding, which react doesn’t and just transition for ajax developer to js requires a lot of effort

Note: Carefully answer as this is a trick question among other react js interview questions

13.Which one you consider better react js or angular

React js is better when the application size is smaller and for new developers learning curve of react js is way smaller than angular as angular is a full-fledged framework with MVC structure. Also with react js transition to react native is possible.

14. Why react is separated from react dom?

They both are separated because the fact react has extended application for mobile via react-native language so react library is for both mobile and web applications whereas react-dom is limited to web applications only.

15. What would you be comfortable in migrating from react js to react native or from react js to angular?

This is a tricky among the all react js interview questions. React Native would open the pathways for mobile application development whereas with angular one can master front-end web development. At the end of the day a developer must be comfortable to grasp faster and implement the skills on the project to come.

So, these were among the most asked react js interview questions. Do checkout similar Posts.

Frequently Asked Questions

Its better to take few months and develop an app first.

Well atleast you can become a part of the present atleast.

Angular as its a framework, not a library and pretty easy to scale.

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Comments Section:


Nov 13, 2020

Just what I needed