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React Top 25 Interview Questions

Last Updated on September 19, 2023 by Mayank Dham

React, the popular JavaScript library for building user interfaces, has gained widespread adoption in the world of web development. As a React developer, whether you’re preparing for a job interview or simply looking to deepen your knowledge, it’s essential to understand some of the most common and challenging questions that may come up during an interview. In this article, we’ve compiled the top 25 React interview questions and provided comprehensive answers to help you succeed.

React Top 25 Interview Questions

1. What is React, and why is it used?
React is a JavaScript library used to build user interfaces. It’s known for its component-based architecture and efficient rendering, making it suitable for building dynamic web applications.

2. Explain the concept of Virtual DOM in React.
The Virtual DOM is a lightweight copy of the actual DOM. React uses it to optimize updates by minimizing direct manipulation of the real DOM, resulting in improved performance.

3. What is JSX, and how does it differ from HTML?
JSX is a JavaScript extension that allows you to write HTML-like code within JavaScript. It is transpiled into regular JavaScript code, making it possible to use HTML-like syntax within React components.

4. Describe the key differences between class components and functional components.
Class components are ES6 classes that can have state and lifecycle methods. Functional components are simpler, stateless functions that can use React Hooks to manage state and lifecycle.

5. What are props in React, and how do you use them?
Props (short for properties) are used to pass data from parent to child components in React. They are read-only and help in creating reusable and dynamic components.

6. Explain React component lifecycle methods and their order of execution.
React component lifecycle methods include componentDidMount, componentDidUpdate, and componentWillUnmount. They define when and how components are created, updated, and destroyed.

7. What is state in React? How is it different from props?
State is an internal data store within a component that can be changed over time. It is mutable and used for managing component-specific data. Props, on the other hand, are read-only and passed from parent to child components.

8. What is React Router, and why is it used?
React Router is a library used for adding client-side routing to React applications. It allows developers to create single-page applications with multiple views.

9. What is Redux, and how does it work with React?
Redux is a state management library for JavaScript applications. It helps manage application state in a predictable way and can be used with React via the react-redux library.

10. Explain the purpose of keys in React lists.
Keys are used to identify and differentiate elements in a list of React components. They are essential for optimizing rendering and maintaining component state.

11. What is React Context, and when would you use it?
React Context is an API for sharing the state between components without having to pass props through every level of the component tree. It’s useful for managing the global application state.

12. What are React Hooks, and what are some commonly used hooks?
React Hooks are functions that allow you to use state and other React features in functional components. Commonly used hooks include useState, useEffect, and useContext.

13. What is lazy loading in React, and why is it important?
Lazy loading is a technique that loads components or resources asynchronously when they are needed, enhancing application performance by reducing initial load times.

14. How can you optimize the performance of a React application?
Performance optimization techniques in React include code splitting, memoization, minimizing unnecessary re-renders, and using production builds.

15. What are controlled and uncontrolled components in React forms?
Controlled components are components whose form elements are controlled by React’s state. Uncontrolled components rely on the DOM for their state.

16. What are React Fragments, and why are they used?
React Fragments are used to group multiple elements without adding an extra node to the DOM. They help improve component structure and maintainability.

17. Explain the concept of error boundaries in React.
Error boundaries are components that catch and handle errors that occur during rendering, preventing the entire application from crashing.

18. How can you conditionally render components in React?
Conditional rendering in React can be achieved using if statements, the ternary operator, or logical operators like && and || in JSX.

19. What is the purpose of the shouldComponentUpdate method?
shouldComponentUpdate is a lifecycle method used to optimize rendering by determining whether a component should re-render based on changes in its props or state.

20. What is the significance of the key prop when rendering lists, and what happens if it’s not used?
The key prop is used to identify and track individual elements in a list. Without it, React may have difficulty efficiently updating the list and may lead to unexpected behavior.

21. How does React handle forms, and what are controlled components?
React manages form elements using controlled components, where form element values are controlled by React’s state. This allows React to update and validate form inputs easily.

22. What is the purpose of the useEffect hook in React?
useEffect is used for managing side effects in functional components, such as data fetching, DOM manipulation, and subscribing to data sources. It replaces lifecycle methods like componentDidMount and componentDidUpdate.

23. What are portals in React, and why are they useful?
Portals allow you to render a component’s children at a different location in the DOM, which can be useful for creating modals, tooltips, or popovers that are not confined to the component’s parent hierarchy.

24. Explain the concept of context providers and consumers in React.
Context providers and consumers are part of the React Context API. Providers supply data to the context, while consumers access that data from any part of the component tree, making it easier to share data between components.

25. How can you secure a React application against common security vulnerabilities?
Securing a React application involves practices like input validation, avoiding cross-site scripting (XSS) attacks, implementing proper authentication and authorization, and protecting against cross-site request forgery (CSRF) attacks.

Mastering React and performing well in React interviews requires a solid understanding of the library’s fundamentals and best practices. These top 25 React interview questions and answers should serve as a valuable resource to help you prepare and demonstrate your expertise in React development during interviews. Additionally, consider exploring more advanced topics and keeping up with the latest React developments to stay at the forefront of web development.

FAQs related to React Top 25 Interview Questions

Below are some of the React Top 25 Interview questions:

1. What is JSX, and why is it used in React?
JSX is a syntax extension for JavaScript used in React to describe the structure of UI components. It allows developers to write HTML-like code within JavaScript.

2. Explain the concept of the Virtual DOM and how it contributes to React’s performance.
The Virtual DOM is a lightweight representation of the actual DOM. React uses it to optimize updates by minimizing direct manipulation of the real DOM, resulting in improved performance.

3. What are React components, and what are the benefits of using them?
React components are reusable, self-contained units of code that encapsulate UI elements and behavior. They promote modularity, reusability, and maintainability in applications.

4. What are props in React, and how are they used to pass data between components?
Props (short for properties) are used to pass data from parent to child components in React. They are read-only and help in creating dynamic and reusable components.

5. the difference between state and props in React.
State is used to manage component-specific data that can change over time and is mutable within the component. Props are read-only and are used for passing data from parent to child components.

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