10 common React Js interview questions.
Tags: react, interview, webdev, javascript
Published: 2023-09-21 06:35:57

**What is React.js, and what are its key features?**

**Answer:** React is an open-source JavaScript library for building user interfaces. Its key features include a virtual DOM for efficient rendering, component-based architecture, one-way data flow, and a strong developer community.

**Explain the concept of Virtual DOM in React.**

**Answer:** The Virtual DOM is a lightweight copy of the real DOM. React uses it to improve performance by minimizing direct manipulation of the actual DOM. When there's a change in the state of a component, React creates a new Virtual DOM representation and compares it with the previous one to determine the minimal set of changes needed to update the real DOM.

**What is JSX in React, and why is it used?**

**Answer:** JSX (JavaScript XML) is a syntax extension for JavaScript used in React to describe what the UI should look like. It allows you to write HTML-like code within JavaScript, making it more readable and intuitive. JSX is later transpiled to JavaScript using tools like Babel.

**Explain the difference between functional components and class components in React.**

**Answer:** Functional components are stateless and are defined as JavaScript functions. They receive props and return a rendered JSX. Class components, on the other hand, are ES6 classes that can hold state and have lifecycle methods. With React Hooks, functional components can also manage state and side effects, blurring the distinction further.

**What are React Props?**

**Answer:** Props (short for properties) are a mechanism for passing data from parent to child components in React. They are read-only and help make components reusable and customizable.

**What is the significance of setState() in React, and how does it work?**

**Answer:** setState() is a method used to update the state of a React component. When setState() is called, React re-renders the component and its child components. It takes an object as an argument, merging it with the current state, and then re-renders the component.

**Explain React Hooks.**

**Answer:** React Hooks are functions that let you "hook into" state and lifecycle features from functional components. They provide a way to use state and other React features without writing class components. Commonly used hooks include useState, useEffect, useContext, and useReducer.

**What is the purpose of the use effect hook in React?**

**Answer:** The useEffect hook is used for handling side effects in functional components. It can be used to perform actions like data fetching, DOM manipulation, or setting up subscriptions after the component has rendered. It replaces lifecycle methods like componentDidMount and componentDidUpdate in class components.

**What is React Router, and why is it used?**

**Answer:** React Router is a popular routing library for React applications. It allows you to create client-side navigation and handle routing in a single-page application. React Router is used to define routes, route parameters, and navigation between different views/components in a React application.

**Explain the concept of props drilling in React.**

**Answer:** Props drilling occurs when you need to pass data through multiple levels of nested components. It can lead to messy and less maintainable code. To avoid props drilling, you can use state management libraries like Redux or Context API to share data between distant components.

**These are the 10 questions I've found also I've faced on my own interviews**

**Check out this blog where I've suggested [10 Exciting Projects for Junior Developers to Level Up Their Skills](https://dev.to/mahfuzurrahman01/10-exciting-projects-for-junior-developers-to-level-up-their-skills-1h5l)**