React Interview Questions for Freshers
1. What is React and why is it used?
React is a JavaScript library for building user interfaces. It’s used for creating fast, interactive UIs for web applications.
2.What is JSX?
JSX (JavaScript XML) is a syntax extension for JavaScript that allows you to write HTML-like code in React.
3.What are components in React?
Components are the building blocks of React applications. They are reusable and independent pieces of UI.
4.Explain the concept of Virtual DOM.
Virtual DOM is a lightweight copy of the actual DOM. React uses it to improve performance by minimizing DOM manipulation operations.
5.What is the significance of keys in React?
Keys are used to identify unique Virtual DOM elements, enabling efficient updates of lists and children components.
6.What are props in React?
Props (short for properties) are a way to pass data from parent to child components in React.
7.What are the differences between class components and functional components?
Class components are ES6 classes that extend from React.Component and have their own state. Functional components are JavaScript functions that take props as input.
8.What is the useState hook used for?
useState is a hook that allows functional components to have state variables.
9.Explain the useEffect hook.
useEffect is a hook that allows functional components to perform side effects.
10.What are React fragments?
React fragments allow you to group multiple elements without adding extra nodes to the DOM.
React Interview Questions for Intermediate Level
1.What is prop drilling? How can it be avoided?
Prop drilling refers to the process of passing props down multiple levels of nested components. It can be avoided by using context or state management libraries.
2.What is the useContext hook used for?
useContext is a hook used for consuming context in functional components.
3.What are higher-order components (HOCs) and when are they used?
HOCs are functions that take a component as input and return a new component with enhanced functionality. They are used for code reuse and logic abstraction.
4.Explain the concept of controlled components.
Controlled components are components whose form elements’ values are controlled by React state.
5.What is error boundary in React?
Error boundaries are React components that catch JavaScript errors in their child component tree during rendering.
6.What is the useMemo hook used for?
useMemo is a hook that memoizes expensive computations to avoid unnecessary re-renders.
7.How does React Router work?
React Router is a library for implementing navigation and routing in React applications.
8.What are refs in React?
Refs are a way to access DOM nodes or React elements created in the render method.
9.What is the useCallback hook used for?
useCallback is a hook that memoizes callback functions to prevent unnecessary renders.
10.Explain the concept of context in React.
Context provides a way to pass data through the component tree without having to pass props manually at every level.
React Interview Questions for Experienced Level
1.What are the key differences between React class components and functional components with hooks?
Class components have their own state and lifecycle methods, while functional components with hooks are simpler and more lightweight.
2.What are the advantages of using Redux with React?
Redux provides a centralized state management solution for React applications, making it easier to manage complex state and data flow.
3.Explain server-side rendering (SSR) in React.
Server-side rendering is a technique used to render React components on the server and send the HTML to the client.
4.What are the limitations of React?
React is a view library and does not provide built-in solutions for features like routing, state management, and form validation.
5.How does React handle performance optimization?
React uses techniques like memoization, Virtual DOM, and shouldComponentUpdate to optimize performance.
6.What are the best practices for structuring a React application?
Best practices include organizing files by feature, using meaningful component names, and separating presentational and container components.
7.What are hooks in React and how do they work?
Hooks are functions that enable functional components to use state and lifecycle features previously available only in class components.
8.What is the difference between React and React Native?
React is a library for building web user interfaces, while React Native is a framework for building mobile applications using React.
9.Explain the concept of lazy loading in React.
Lazy loading is a technique used to load components or assets asynchronously when they are needed, rather than loading everything upfront.
10.What are the key considerations for optimizing React applications for SEO?
Considerations include server-side rendering, using semantic HTML, and providing metadata for search engines.
11.What are the differences between React and Angular?
React is a library, while Angular is a full-fledged framework. React uses a virtual DOM, while Angular uses a real DOM.
12.How do you handle form validation in React?
Form validation in React can be handled using libraries like Formik or by manually implementing validation logic.
13.What is the purpose of the useEffect hook’s dependency array?
The dependency array allows you to specify which values the effect depends on, triggering the effect only when those values change.
14.Explain the concept of memoization in React.
Memoization is the process of caching the results of expensive function calls to improve performance.
15.How do you handle authentication in a React application?
Authentication in React can be handled using libraries like Firebase or by implementing custom authentication logic with JWT.
16.What are the different lifecycle methods in React class components?
Lifecycle methods include componentDidMount, componentDidUpdate, componentWillUnmount, etc.
17.What are the advantages of using React Hooks?
Hooks allow for better code organization, reusability, and encapsulation of stateful logic in functional components.
18.How do you optimize the performance of React applications?
Performance optimization techniques include code splitting, lazy loading, memoization, and minimizing re-renders.
19.Explain the concept of code splitting in React.
Code splitting is a technique used to split your code into smaller bundles that can be loaded on demand, improving the initial load time of your application.
20.What are the limitations of using context in React?
Context is not suitable for passing large amounts of data, as it can lead to performance issues. It’s also less flexible than props for passing data between components.