React js interview questions

REACT JS INTERVIEW QUESTIONS

React JS, Blog, Must Read / By / July 25, 2024

The Ultimate Guide to React JS Interview Questions and answer

Looking for a job in front-end development? You’ll likely need to ace an interview focused on React JS. Whether you’re a fresher just starting out, have a few years of experience, or are a seasoned developer, being prepared is crucial. In this comprehensive guide, we will cover various React JS interview questions, provide insightful answers, and give you the confidence to succeed. Let’s dive in!

Table of Contents

Sr#Headings
1Introduction
2Basic React Interview Questions
3Advanced React JS Interview Questions
4React JS Interview Questions for Freshers
5React JS Interview Questions for Experienced Developers
6React JS Interview Questions for 5 Years Experience
7How to Prepare for a React JS Interview
8Common Mistakes to Avoid
9React JS Interview Questions on GitHub
10React JS Interview Questions PDF
11Conclusion
12FAQs

Introduction

React JS has become a staple in modern web development due to its efficiency and flexibility. But when it comes to job interviews, knowing React isn’t enough. You need to be prepared to answer a range of questions that test your understanding and application of the framework. This article will help you navigate these questions, from the basics to more advanced topics, ensuring you’re ready for your next interview.

Basic React Interview Questions

Let’s start with some fundamental questions you might encounter:

1. What is React JS?

React JS is a JavaScript library developed by Facebook for building user interfaces, particularly single-page applications. It allows developers to create large web applications that can update and render efficiently in response to data changes.

2. Why use React JS?

React JS offers numerous advantages:

  • Reusable Components: Allows for the reuse of components, reducing redundancy.
  • Virtual DOM: Enhances performance by updating only the parts of the DOM that need to change.
  • One-Way Data Binding: Provides a unidirectional data flow, which makes debugging easier.
  • Large Ecosystem: A vast array of tools, libraries, and community support.

3. What are the main features of React JS?

Key features include:

  • JSX: A syntax extension that allows mixing HTML with JavaScript.
  • Components: The building blocks of a React application.
  • State and Props: Mechanisms to manage and pass data.
  • Lifecycle Methods: Hooks to manage component lifecycle events.

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Advanced React JS Interview Questions

4. What are React components?

React components are the core building blocks of a React application. They encapsulate logic and UI, making code more modular and reusable.

5. Types of React Components

  • Functional Components: Simple JavaScript functions that return JSX.
  • Class Components: ES6 classes that extend React.Component and can manage state and lifecycle methods.

6. What are the differences between Functional and Class Components?

  • Syntax: Functional components use functions, while class components use ES6 classes.
  • State Management: Functional components use hooks like useState, whereas class components use this.state.
  • Lifecycle Methods: Class components have built-in lifecycle methods; functional components use hooks like useEffect.

7. What is JSX?

JSX stands for JavaScript XML. It is a syntax extension that allows writing HTML elements in JavaScript and placing them in the DOM.

Advantages of Using JSX

  • Readability: Makes the code more readable and easier to understand.
  • Efficiency: Compiles to JavaScript, enabling performance optimizations.

JSX Syntax and Examples

const element = <h1>Hello, world!</h1>;

In the example above, JSX allows HTML-like syntax in JavaScript, which will be compiled to React.createElement.

8. What are the state and props in React?

  • State: An object that determines how that component renders and behaves.
  • Props: Short for properties, these are read-only attributes passed from parent to child components.

9. Differences between State and Props

  • Mutability: State is mutable and can change over time, while props are immutable.
  • Usage: State is used for local component data, props are used to pass data between components.

10. How to Use State and Props

Example of using state:

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }
  render() {
    return <h1>{this.state.count}</h1>;
  }
}

11. What is the difference between state and props in React?

State is a data structure that starts with a default value when a component mounts. It is mutable and can be changed over time. Props (short for properties) are a component’s configuration. Props are immutable and are passed down from parent components to child components.

12. Can you explain the lifecycle methods of React components?

React components have several lifecycle methods that you can override to run code at particular times in the process:

  • componentDidMount(): Executed after the first render.
  • componentDidUpdate(prevProps, prevState): Called after updating takes place.
  • componentWillUnmount(): Used for cleanup, like clearing timers or canceling network requests.

13. How to Handle Events in React

React events are handled similarly to HTML events but use camelCase. Event handlers are passed as functions.

Example of Event Handling

class Toggle extends React.Component {
  constructor(props) {
    super(props);
    this.state = { isToggleOn: true };
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState(state => ({
      isToggleOn: !state.isToggleOn
    }));
  }

  render() {
    return (
      <button onClick={this.handleClick}>
        {this.state.isToggleOn ? 'ON' : 'OFF'}
      </button>
    );
  }
}

14. What is Conditional Rendering in React?

Conditional rendering allows components to render differently based on certain conditions.

Techniques for Conditional Rendering

  • Ternary Operator: condition ? <ComponentA /> : <ComponentB />
  • Logical AND Operator: condition && <Component />
  • If-Else Statements: Using traditional if-else within the render method.

15. How to Render Lists in React?

Lists are rendered using the map() method to iterate over an array and return a list of elements.

Importance of Keys in Lists

Keys help React identify which items have changed, are added, or are removed. They should be unique among siblings.

Best Practices for Using Keys

  • Use unique identifiers.
  • Avoid using indexes as keys if items can be reordered.

16. Handling Forms in React

Forms in React can be controlled (where form data is handled by React state) or uncontrolled (where form data is handled by the DOM).

17. Controlled vs. Uncontrolled Components

  • Controlled Components: Form data is handled by React through state.
  • Uncontrolled Components: Form data is handled by the DOM itself.

18. What is React Router?

React Router is a standard library for routing in React. It enables navigation among views of various components in a React application.

19. Importance of React Router

Allows for dynamic routing and helps manage URLs and rendering of components based on the route.

Basic Usage and Examples

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

function App() {
  return (
    <Router>
      <div>
        <nav>
          <ul>
            <li>
              <Link to="/">Home</Link>
            </li>
            <li>
              <Link to="/about">About</Link>
            </li>
          </ul>
        </nav>

        <Route path="/" exact component={Home} />
        <Route path="/about" component={About} />
    </div>
<Router>
)}

20. React JS Interview Questions for Freshers

If you’re just starting out, here are some questions tailored for you:

21. What is JSX?

JSX stands for JavaScript XML. It allows you to write HTML elements in JavaScript and place them in the DOM without using functions like createElement() or appendChild().

22. How do you create a React component?

There are two ways to create a React component:

  • Function Component: A simple JavaScript function that returns JSX.
  • Class Component: A more complex component created using ES6 classes.

23. What is a state in React and how is it used?

State is an object that determines how a component renders and behaves. State is managed within the component (similar to variables declared within a function).

React JS Interview Questions for Experienced Developers

24. How do you manage state in a React application?

State can be managed in various ways:

  • Local State: Managed within a component using useState or this.setState in class components.
  • Global State: Managed using context or state management libraries like Redux or MobX.

25. What is Redux and how does it work with React?

Redux is a state management library that provides a centralized store for all the components in an application. It works with React by using actions and reducers to manage state changes predictably.

26. Can you explain React Hooks?

React Hooks are functions that let you use state and lifecycle features in functional components. Key hooks include:

  • useState: For managing state.
  • useEffect: For performing side effects in function components.
  • useContext: For accessing context within a component.

React JS Interview Questions for 5 Years Experience

27. How do you optimize a React application?

Optimizations can include:

  • Memoization: Using React.memo to prevent unnecessary re-renders.
  • Code-Splitting: Using React.lazy and Suspense for dynamic imports.
  • Use of PureComponent: To implement a shallow comparison on props and state.

28. Explain the concept of Higher-Order Components (HOC).

HOCs are functions that take a component and return a new component. They are used for reusing component logic.

29. What is the Context API and when would you use it?

The Context API is used to pass data through the component tree without having to pass props down manually at every level. It’s useful for global data like themes, user information, etc.

How to Prepare for a React JS Interview

30. Study the Fundamentals

Ensure you understand the core concepts of React, such as components, state, props, and lifecycle methods. Websites like the React documentation are great resources.

31. Practice Coding

Implement various projects and solve problems on platforms like GitHub. Practice common algorithms and data structures as they are often part of technical interviews.

32. Mock Interviews

Participate in mock interviews to get a feel for the types of questions that might be asked. Use platforms like Pramp or LeetCode for practice.

Common Mistakes to Avoid

33. Overcomplicating Solutions

Stick to simple and clean code. Avoid the temptation to over-engineer your solutions.

34. Neglecting Performance Optimization

Understand and implement best practices for performance optimization to make your applications efficient.

35. Ignoring the Basics

Don’t overlook the fundamentals in favor of advanced topics. Strong foundational knowledge is crucial.

React JS Interview Questions on GitHub

Many developers share interview questions on GitHub. You can find repositories with a compilation of questions that can help you prepare. Simply search for “React JS interview questions” on GitHub to find these resources.

React JS Interview Questions PDF

We offer downloadable PDFs with interview questions and answers. These can be handy for offline study. Look for reputable sources to ensure the information is accurate and up-to-date.

React JS Interview QuestionsDownload

Conclusion

Preparing for a React JS interview requires a mix of understanding the basics, diving into more advanced concepts, and practicing coding problems. Whether you’re a fresher or an experienced developer, this guide should give you a solid foundation to tackle your interview with confidence.

FAQs

1. What are the most common React JS interview questions?

Common questions include: What is React? What is JSX? How does the virtual DOM work? Explain the differences between state and props.

2. How can I prepare for a React JS interview as a fresher?

Focus on understanding basic concepts, building small projects, and reviewing fundamental interview questions. Utilize resources like GitHub and online coding platforms.

3. What advanced topics should I study for a React JS interview?

Study state management (Redux), React hooks, performance optimization techniques, and the Context API.

4. Where can I find React JS interview questions online?

Websites like GitHub, LeetCode, and various coding forums often have extensive lists of interview questions and answers.

5. Is it helpful to download React JS interview questions PDFs?

Yes, PDFs can be a convenient way to study, especially if they come from reliable sources. They allow you to review questions and answers offline.

Some useful link:
react js job support –https://tekody.com/services/react-js-job-support/
How to setup react project: https://tekody.com/blogs/setup-react-project-using-create-react-app/
Learn React – https://react.dev/learn

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