React JS Quiz - Multiple Choice Questions (MCQ)

React.js has gained immense popularity among developers due to its efficiency, reusability, and performance. If you're a React.js enthusiast or want to assess your knowledge of this JavaScript library, this quiz is for you. This quiz consists of 15+ multiple-choice questions designed to test your understanding of React.js concepts and best practices. Let's dive in and see how well you fare!

Learn React JS: React JS Tutorial for Beginners

Check out 100+ quiz questions: 100+ Quiz Questions to Test Your Java, Spring Boot, Microservices, Hibernate, REST API Skills

1. What is React.js?

a) A JavaScript framework for building user interfaces.

b) A server-side programming language.

c) A database management system.

d) A front-end CSS framework.

Answer: 

a) A JavaScript framework for building user interfaces. 

Explanation: 

React.js is a JavaScript library, not a framework, that is primarily used for building user interfaces (UIs). It allows developers to create reusable UI components and efficiently update the UI based on data changes.

2. What does JSX stand for? 

a) JavaScript XML 

b) Java Syntax Extension 

c) JSON Xchange Schema 

d) JavaScript Xerography 

Answer: 

a) JavaScript XML 

Explanation: 

JSX stands for JavaScript XML. It is an extension to JavaScript that allows you to write HTML-like syntax within your JavaScript code in React.js. JSX makes it easier to define the structure and layout of components. 

3. Which lifecycle method is invoked immediately after a component is rendered on the DOM?

a) componentDidMount 

b) componentDidUpdate 

c) componentWillMount 

d) componentWillRender 

Answer: 

a) componentDidMount 

Explanation: 

The componentDidMount lifecycle method is invoked immediately after a component is rendered on the DOM. It is commonly used to fetch data from an API, set up event listeners, or perform any necessary initialization tasks. 

4. What is the purpose of the "key" prop in React? 

a) It uniquely identifies a component in an array of components. 

b) It determines the visual styling of a component. 

c) It specifies the route for navigation within a React application. 

d) It defines the data type of a component's prop. 

Answer: 

a) It uniquely identifies a component in an array of components. 

Explanation: 

The "key" prop is used to provide a unique identifier to each component in an array of components. React uses this key to efficiently update and reconcile the components' virtual DOM when their positions or states change. 

5. What is the state of React class component? 

a) A JavaScript method for sorting arrays. 

b) A built-in object that stores component data. 

c) A CSS class used for component styling. 

d) A React component's initial render method. 

Answer: 

b) A built-in object that stores component data. 

Explanation: 

State is a built-in object in React that allows components to store and manage data. It represents the current state of a component and can be updated using the setState() method. 

6. Which method is used to update the state of a class component in React? 

a) this.updateState() 

b) this.setState() 

c) this.modifyState() 

d) this.changeState() 

Answer: 

b) this.setState() 

Explanation: 

The this.setState() method is used to update the state of a component in React. It accepts a new state object or a function that returns a new state based on the previous state. 

7. What is the purpose of the React Router library? 

a) To handle HTTP requests in React applications. 

b) To manage and synchronize component states. 

c) To manage navigation and routing in React applications. 

d) To optimize the performance of React applications. 

Answer: 

c) To manage navigation and routing in React applications. 

Explanation: 

The React Router library provides a routing solution for React applications. It allows developers to define routes, handle navigation, and render specific components based on the current URL.

8. What is the purpose of PropTypes in React? 

a) To define the expected data types of component props. 

b) To validate HTML syntax within JSX code. 

c) To handle form validation in React applications. 

d) To provide default values for component props. 

Answer: 

a) To define the expected data types of component props. 

Explanation: 

PropTypes is a mechanism in React for specifying the expected data types of component props. It helps ensure that the correct data types are passed to components and provides runtime warnings in case of type mismatches. 

9. What is the purpose of React Fragments? 

a) To group multiple components within a single parent component. 

b) To create reusable CSS styles for React components. 

c) To optimize the rendering performance of React components. 

d) To handle asynchronous operations in React applications. 

Answer: 

a) To group multiple components within a single parent component. 

Explanation: 

React Fragments allow you to group multiple components within a single parent component without introducing additional DOM elements. It helps avoid unnecessary wrapper divs and improves the component hierarchy. 

10. Which method is used to render a React component to the DOM? 

a) renderComponent() 

b) ReactDOM.render() 

c) React.render() 

d) component.render() 

Answer: 

b) ReactDOM.render() 

Explanation: 

The ReactDOM.render() method is used to render a React component to the DOM. It takes the component and a target DOM element as arguments and renders the component's output to the specified element in the DOM.

11. What is the purpose of Redux in React applications? 

a) To handle form validation and submission. 

b) To manage and synchronize component states. 

c) To define the expected data types of component props. 

d) To create reusable UI components. 

Answer: 

b) To manage and synchronize component states. 

Explanation: 

Redux is a state management library commonly used with React to manage and synchronize component states in large-scale applications. It provides a predictable state container and facilitates unidirectional data flow. 

12. What is the significance of the virtual DOM in React? 

a) It renders components on the server side. 

b) It optimizes React components for mobile devices. 

c) It provides an in-memory representation of the DOM for efficient updates. 

d) It handles animations and transitions in React applications. 

Answer: 

c) It provides an in-memory representation of the DOM for efficient updates. 

Explanation: 

The virtual DOM in React is an in-memory representation of the actual DOM. It allows React to efficiently update and reconcile changes in the UI by comparing the virtual DOM with the real DOM and updating only the necessary elements. 

13. Which hook is used to add state to functional components in React? 

a) useState 

b) useEffect 

c) useContext 

d) useReducer 

Answer: 

a) useState 

Explanation: 

The useState hook is used to add state to functional components in React. It allows you to declare a state variable and provides a way to update its value. useState hook returns an array with the current state value and a function to update the state.

14. What is the purpose of the useEffect hook in React? 

a) To add state to functional components. 

b) To handle component re-renders. 

c) To perform side effects in functional components. 

d) To handle form submissions in React applications. 

Answer: 

c) To perform side effects in functional components. 

Explanation: 

The useEffect hook is used to perform side effects in functional components. Side effects can include things like fetching data, subscribing to events, or manually updating the DOM. useEffect is called after every render and can be used to manage the side effects of a component.

15. What is the purpose of the useParams hook in React Router? 

a) To handle form validation in React.js 

b) To retrieve query parameters from the URL 

c) To extract URL parameters from a route 

d) To manage the state of route transitions 

Answer: 

c) To extract URL parameters from a route 

Explanation: 

The useParams hook in React Router is used to extract URL parameters from a route. URL parameters are dynamic parts of the URL that can be accessed and used within a component to customize its behavior based on the specific route.

16. How can you access form input values in React.js? 

a) By using the document.getElementById() method 

b) By using the event.target.value property 

c) By using the useState hook and setting the initial value 

d) By using the useRef hook and the current property 

Answer: 

b) By using the event.target.value property 

Explanation: 

In React.js, you can access form input values by using the event.target.value property within an event handler function. This property gives you the current value of the input element that triggered the event and allows you to capture and use the input data.

Conclusion

In this React JS quiz, we covered various aspects of React JS, including its basic concepts, JSX, component lifecycle, hooks, form handling, routing, and more. React JS is a powerful JavaScript library for building user interfaces, and having a good understanding of its fundamentals is essential for developing robust and efficient applications. Through the quiz questions, you had the opportunity to test your knowledge and expand your understanding of React JS. 

Learn React JS: React JS Tutorial for Beginners

Check out 100+ quiz questions: 100+ Quiz Questions to Test Your Java, Spring Boot, Microservices, Hibernate, REST API Skills

Keep practicing, experimenting, and building with React JS to become a proficient front-end developer.