React JS Interview Questions: A Comprehensive Guide


Are you preparing for a React.js interview? Congratulations! React js is a popular JavaScript library for building user interfaces, and nailing your interview can open doors to exciting career opportunities. To help you succeed, we’ll explore some common interview questions and provide code samples that demonstrate your React js prowess. So, let’s dive right in!

React JS Interview Questions: A Comprehensive Guide

1. What is React js, and how does it differ from other JavaScript libraries or frameworks?

This question is a classic icebreaker. React js is a JavaScript library for building user interfaces that focuses on the declarative approach. It allows you to create interactive and reusable UI components. You might answer like this:

import React from 'react';

function MyComponent() {
  return <div>Hello, React!</div>;

export default MyComponent;

Here, we’ve defined a simple functional component using React, demonstrating its core idea of reusable UI building blocks.

2. What are props in React, and how are they used?

Props (short for properties) are a fundamental concept in React js. They allow you to pass data from a parent component to a child component. Here’s a code example:

function ParentComponent() {
  const name = "John";

  return <ChildComponent name={name} />;

function ChildComponent(props) {
  return <div>Hello, {}!</div>;

In this code, the name prop is passed from ParentComponent to ChildComponent.

3. Explain state in React and how it differs from props.

State is an internal data store for a component, and it can change over time. It is used to manage data that should be dynamic and interactive. Contrasting with props, which are read-only, state is mutable and managed within the component. Here’s a simple state example:

import React, { Component } from 'react';

class Counter extends Component {
  constructor(props) {
    this.state = { count: 0 };

  render() {
    return (
        <p>Count: {this.state.count}</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>

In this example, count is maintained as the component’s internal state.

4. What is the virtual DOM, and how does React use it for performance optimization?

The virtual DOM is a lightweight copy of the actual DOM. React uses it to minimize direct manipulation of the real DOM, which can be slow. Instead, React updates the virtual DOM and calculates the most efficient way to update the real DOM, improving performance. Here’s an illustration:

const oldElement = <div>Hello, React!</div>;

const newElement = <div>Hello, React and virtual DOM!</div>;

React would identify that only a portion of the real DOM needs to be updated when transitioning from oldElement to newElement.

5. What is the significance of keys in React js lists, and how are they used?

Keys are essential when rendering dynamic lists of elements. They help React identify which items have changed, been added, or removed efficiently. For example:

function TodoList({ todos }) {
  return (
      {, index) => (
        <li key={}>{todo.text}</li>

In this code, the key attribute ensures React can track changes in the list.


Mastering React.js for interviews is not just about memorizing answers but understanding the core concepts and demonstrating your coding skills. We’ve covered some common questions and provided code samples to help you prepare. Remember to practice, explore React’s documentation, and keep up with the latest trends. Good luck with your React.js interview, and may you land that dream job!

Frequently Asked Questions (FAQs)

  1. How can I prepare for a React.js interview? Preparing for a React.js interview involves understanding the fundamental concepts of React, practicing coding exercises, and reviewing common interview questions. Utilize online resources, tutorials, and documentation to enhance your knowledge.
  2. What are some common interview questions for React.js? Common interview questions for React.js include topics like props, state, the virtual DOM, component lifecycle, and hooks. You should also be prepared to demonstrate your coding skills through hands-on exercises.

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