Top 20 ReactJS Interview Questions with Examples: Your Preparation Guide

Prepare for your next ReactJS interview with confidence by learning the answers to the top 20 most commonly asked questions. This guide provides in-depth explanations and practical examples to help you understand the fundamental concepts of ReactJS and impress your interviewer.

Top 20 ReactJS Interview Questions with Examples: Your Preparation Guide

Why do we use Keys in ReactJS lists?

Keys in ReactJS lists are used to identify unique elements in the list. Keys help React keep track of which items have changed, are added, or are removed from the list, which optimizes the rendering process. Keys should be assigned to elements inside the array to give the elements a stable identity. Example:

const todoItems = =>{todo.text});

How can the transversal of lists be achieved in ReactJS?

Transversal of lists in ReactJS can be achieved by using the map() function to loop through an array and return a list of elements. Example:

const todoList =, index) =>{todo}

What do you understand about components in React?

Components in React are reusable and self-contained units of code that return a renderable component. Components can receive data from their parent component through props and manage their own state.

Explain the two types of Components in ReactJS?

The two types of components in ReactJS are class components and functional components. Class components are written as JavaScript classes and have access to lifecycle methods and state. Functional components are written as plain JavaScript functions and have access to props only. Example of class component:

class Welcome extends React.Component {
  render() {
    return Hello, {};

Example of functional component:

const Welcome = (props) =>Hello, {};

What are Synthetic events in React?

Synthetic events in React are a cross-browser wrapper around the browser's native event. They are used to handle events in React, such as click events, mouse events, etc. Example:

 alert('Button clicked')}>
  Click me

What are Pure Components in ReactJS?

Pure Components in ReactJS are components that implement shouldComponentUpdate lifecycle method with a shallow comparison of props and state. This allows React to optimize the rendering process by skipping render if the props and state haven't changed. Example:

class TodoListItem extends React.PureComponent {
  render() {
    return (

What are some important features of Redux?

Redux is a predictable state management library for JavaScript apps. Some of its important features are:

  • Single source of truth: The state of the entire application is stored in a single object called the store.
  • State is read-only: The only way to change the state is to dispatch an action, an object describing what happened.
  • Changes are made with pure functions: Reducers, the functions that update the state, are pure functions that take the previous state and an action and return the new state.


const store = createStore(reducer);

store.dispatch({ type: 'ADD_TODO', text: 'Learn Redux' });

// Output: [{ text: 'Learn Redux', completed: false, id: 0 }]

What do you understand about Flux in React?

Flux is an architecture for building web applications with unidirectional data flow. It was developed by Facebook and is often used with React. The basic idea of Flux is to have a centralized store that holds the application state and dispatch actions to update the state. This helps to keep the code organized and predictable.

Why are Routers used in ReactJS?

Routers in ReactJS are used to handle navigation and routing in a single-page application. They allow the user to move between different routes or pages in the application and change the URL in the address bar. Example:

import {
  BrowserRouter as Router,
} from "react-router-dom";

function App() {
  return (

What are some disadvantages associated with the ReactJS framework?

Some disadvantages of ReactJS are:

  • Steep learning curve: React can be difficult to learn and understand, especially for beginners.
  • Overly complex code: React can sometimes lead to overly complex code, especially when used in combination with Redux and other libraries.
  • Poor documentation: While React has good documentation, it can be hard to find solutions to specific problems due to its large community and fast pace of development.
  • JavaScript fatigue: React requires the use of JavaScript and its ecosystem, which can be overwhelming for some developers.

Why can’t browsers read JSX? How can browsers be made to read JSX?

Browsers cannot read JSX because it is an extension of JavaScript syntax that is not supported natively by web browsers. JSX needs to be transpiled, or transformed, into JavaScript code that can be understood and executed by browsers. This can be done using a transpiler such as Babel. Example:

const element =Hello, world!;

After transpilation:

const element = React.createElement("h1", null, "Hello, world!");

What do you understand about Higher-Order Components in ReactJS?

Higher-Order Components (HOCs) in ReactJS are advanced techniques in React for reusing component logic. HOCs are functions that take a component and return a new component with additional props. Example:

const EnhancedComponent = higherOrderComponent(WrappedComponent);

What do you understand by References in ReactJS?

References in ReactJS are a way to access the properties of a DOM element in React. They are created using the React.createRef() method and attached to React elements via the ref attribute. For example, consider a component that renders an input field:

import React, { useRef } from 'react';

function InputField() {
  const inputRef = useRef(null);

  const handleClick = () => {
  return ( Focus Input
); } export default InputField;

In this example, the input field's reference is stored in the inputRef constant, which is created using useRef(). The ref attribute is then attached to the input field, allowing it to be accessed and manipulated in the handleClick function when the button is clicked.

What are Props in ReactJS?

Props, short for "properties", are inputs passed to React components. They are used to pass data and event handlers from a parent component to its children components. For example, consider a component that renders a user's name:

import React from 'react';

function UserName({ name }) {
  return {name} } export default UserName;

In this example, the UserName component accepts a name prop, which is used to render the user's name. The prop can be passed down from a parent component as follows:

import React from 'react'; import UserName from './UserName'; function App() { return (
); } export default App;

How do you modularize code in the ReactJS framework?

In ReactJS, code can be modularized by creating components. Components allow you to split your UI into reusable and independent pieces, making your code easier to manage and maintain. For example, consider a component that renders a header with a logo and a navigation bar:

import React from 'react';
import Logo from './Logo';
import Navbar from './Navbar';
function Header() {
  return (

export default Header;

In this example, the Header component is composed of two smaller components, Logo and Navbar, which can be reused in other parts of the application. This allows you to keep your code organized and maintainable.

What is the use of Webpack in React?

Webpack is a module bundler for JavaScript applications, including React. It takes modules with dependencies and generates static assets representing those modules. In the context of a React application, Webpack can be used to package the code, including the React components, and their dependencies into a single file or a few files that can be served to the browser. 


// index.js
import React from 'react';
import ReactDOM from 'react-dom';


Hello, World!

, document.getElementById('root') );

// webpack.config.js
const path = require('path');

module.exports = {
  mode: 'development',
  entry: './index.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js'

What is Babel in ReactJS?

Babel is a JavaScript compiler that can transform modern JavaScript code into a form that can be run in older JavaScript engines, including those found in web browsers. In the context of React, Babel is often used to transpile JSX, a syntax extension for JavaScript that allows for writing HTML-like elements in JavaScript.


// example.jsx
import React from 'react';
const Example = () => (

Hello, World!

export default Example;

// .babelrc
  "presets": [

What is Prop-drilling in ReactJS?

Prop drilling is a term used to describe the process of passing data from a parent component to a child component, through intermediate components that don't use the data. This is often necessary when you need to pass data that is not directly accessible to a component deep in the component tree.


// App.js
import React from 'react';
import Grandchild from './Grandchild';

const App = () => {
  const data = { name: 'John Doe' };

  return (

export default App;

// Child.js
import React from 'react';

const Child = ({ data }) => (

export default Child;

// Grandchild.js
import React from 'react';

const Grandchild = ({ data }) => (

Hello, {}!


export default Grandchild;

What are Error Boundaries in ReactJS?

Error Boundaries are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of the component tree that crashed. Error boundaries catch errors during rendering, in lifecycle methods, and in constructors of the whole tree below them. Here's an example of an Error Boundary component:

class ErrorBoundary extends React.Component {
  constructor(props) {
    this.state = { hasError: false };
  static getDerivedStateFromError(error) {
    // Update state so the next render will show the fallback UI.
    return { hasError: true };
  componentDidCatch(error, errorInfo) {
    // You can also log the error to an error reporting service
    console.error(error, errorInfo);
  render() {
    if (this.state.hasError) {
      // You can render any custom fallback UI

Something went wrong.

    return this.props.children;


What do you understand about the Strict mode in React?

Strict Mode is a development-only feature in React that enables additional checks and warnings for components and the code they call. This helps you find potential problems in your code early, before they cause issues in production. Here's an example of how you can use Strict Mode in your React app:

import React from 'react';

function App() {
  return (

export default App;

It is recommended to only use Strict Mode during development and not in production, as it might slow down the performance of your app.

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