React JS is one of the most popular JavaScript libraries for building user interfaces, especially single-page applications. As a result, React JS interview questions are common during tech job interviews. In this article, we'll cover the top 25 React JS interview questions to help you prepare for your next interview.

1. What is React JS?

Answer: React JS is an open-source JavaScript library developed by Facebook for building reusable UI components. It is mainly used to build single-page applications that handle user interactions efficiently and maintain a consistent look and feel across the entire application.

2. What are the main features of React JS?

Answer: Some of the main features of React JS include:

  • Virtual DOM
  • One-way data binding
  • JSX
  • Components
  • React Hooks
  • React Router

3. What is JSX?

Answer: JSX (JavaScript XML) is a syntax extension for JavaScript that allows you to write HTML-like code within your JavaScript code. This makes it easier to create and modify the UI of your application.

4. What is the difference between a functional component and a class component?

Answer: A functional component is a JavaScript function that returns JSX. It does not have state or lifecycle methods. A class component is a JavaScript class that extends React.Component and can have state and lifecycle methods.

5. What is the Virtual DOM?

Answer: The Virtual DOM is a lightweight in-memory representation of the actual DOM. React uses the Virtual DOM to determine the most efficient way to update the actual DOM when the state of a component changes.

6. What are props in React?

Answer: Props (short for "properties") are the way components receive data from their parent components. They are read-only and should not be modified within the component.

7. What is state in React?

Answer: State is an object that holds the data that is local to a component. It is mutable and can be updated using the setState method in class components or the useState hook in functional components.

8. What is the difference between state and props?

Answer: State is mutable and local to a component, while props are read-only and passed down from parent components.

9. What are React hooks?

Answer: React hooks are functions that allow you to use state and lifecycle features in functional components. Some commonly used hooks are useState, useEffect, and useContext.

10. What is the purpose of the useEffect hook?

Answer: The useEffect hook is used to perform side effects, such as fetching data or updating the DOM, in functional components. It can be thought of as a combination of `componentDidMount

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