React MCQ - Multiple Choice Questions

Welcome to the React Quiz for Beginners! This quiz is designed to test your understanding of fundamental React concepts, from JSX syntax and state management to lifecycle methods and event handling.

React is a JavaScript library for building user interfaces. React is widely used to build single-page applications. Whether you’ve just dabbled in React or completed your first project, these 40 multiple-choice questions will challenge your knowledge and help solidify your understanding of this popular JavaScript library. Each question comes with an answer and a brief explanation to clarify core ideas and concepts.

1. What is React primarily used for?

A. Building mobile applications

B. Building server-side applications

C. Building user interfaces for web applications

D. Data analysis

Answer:

C. Building user interfaces for web applications

Explanation:

React is a JavaScript library primarily used for building user interfaces in web applications.

2. Which company developed React?

A. Google

B. Apple

C. Facebook

D. Microsoft

Answer:

C. Facebook

Explanation:

React was developed and is maintained by Facebook.

3. What is JSX in React?

A. A JavaScript extension that allows us to write HTML-like code inside JavaScript

B. A tool for transpiling ES6 to ES5

C. A built-in function to handle state in React

D. A library for adding animations in React components

Answer:

A. A JavaScript extension that allows us to write HTML-like code inside JavaScript

Explanation:

JSX stands for JavaScript XML. It is a syntax extension for JavaScript, recommended by React for describing the UI structure. It allows developers to write HTML structures in a way that looks similar to XML within their JavaScript code, making the UI code more readable and intuitive.

4. What method must every React class component implement?

A. init()

B. componentWillMount()

C. execute()

D. render()

Answer:

D. render()

Explanation:

Every React component must implement the render() method.

5. What is the name of the concept that React uses to efficiently update the user interface?

A. Bootstrap

B. AJAX

C. Virtual DOM

D. WebSockets

Answer:

C. Virtual DOM

Explanation:

React uses a concept called the Virtual DOM to efficiently update the user interface.

6. Which function allows you to create a React component?

A. React.createComponent()

B. React.makeComponent()

C. React.createClass()

D. React.buildComponent()

Answer:

C. React.createClass()

Explanation:

Before the ES6 class syntax, React.createClass() was the way to create a React component.

7. In React, which feature is used pass the data between components?

A. State

B. Properties

C. Elements

D. Props

Answer:

D. Props

Explanation:

In React, data passed into a component is referred to as "props" or properties.

8. In which lifecycle method should you make AJAX requests in a class component?

A. componentWillMount()

B. componentDidMount()

C. render()

D. componentWillUpdate()

Answer:

B. componentDidMount()

Explanation:

Making AJAX requests in the componentDidMount() lifecycle method ensures that the data is fetched as soon as the component is added to the DOM.

9. How can you access the state of a component from inside of a method?

A. this.state

B. this.props.state

C. this.getState()

D. state.this

Answer:

A. this.state

Explanation:

The state of a React component can be accessed with this.state.

10. Which of the following is a valid way to update the state in React class component?

A. this.state.value = 100;

B. this.setState({ value: 100 });

C. state.value = 100;

D. setState({ value: 100 });

Answer:

B. this.setState({ value: 100 });

Explanation:

The correct way to update the state in React is using the this.setState() method.

11. What does props.children refer to?

A. All components should have child components

B. The child components defined within the component

C. Props passed from a parent to its children

D. The DOM nodes generated by the component

Answer:

B. The child components defined within the component

Explanation:

props.children refers to the content placed between the opening and closing tags of a component.

12. Which hook can be used for performing side effects in function components?

A. useEffect

B. useState

C. useProps

D. useRender

Answer:

A. useEffect

Explanation:

The useEffect hook is used to perform side effects in function components, like data fetching, subscriptions, or manually changing the DOM.

13. Which of the following hooks allows you to use state in function components?

A. useState

B. withState

C. thisState

D. haveState

Answer:

A. useState

Explanation:

The useState hook allows function components to use state.

14. What is the primary use of Redux in a React application?

A. Component styling

B. DOM manipulation

C. Managing state

D. Handling forms

Answer:

C. Managing state

Explanation:

Redux is primarily used for managing application state in a centralized store.

15. What is a Higher Order Component (HOC)?

A. A component with a higher state value

B. A component that renders after other components

C. A component that takes another component as an argument

D. A more advanced component

Answer:

C. A component that takes another component as an argument

Explanation:

An HOC is a function that takes a component and returns a new component with additional props or functionalities.

16. What is a Fragment in React?

A. A part of the React library used for AJAX calls

B. A type of storage similar to localStorage

C. A group of components

D. A lightweight way to group multiple elements without adding an extra node to the DOM

Answer:

D. A lightweight way to group multiple elements without adding an extra node to the DOM

Explanation:

React Fragment allows grouping of multiple children without adding extra nodes to the DOM.

17. Which of the following is not a lifecycle method in React class components?

A. render()

B. componentToRender()

C. componentDidMount()

D. shouldComponentUpdate()

Answer:

B. componentToRender()

Explanation:

componentToRender() is not a lifecycle method in React. The others are valid lifecycle methods.

18. What is a key in React?

A. A method to unlock premium React features

B. A way to target CSS styles to specific components

C. A special string attribute required when creating lists of elements

D. The main method to store data in the component

Answer:

C. A special string attribute required when creating lists of elements

Explanation:

Keys in React help identify which items in a list have changed, are added, or are removed.

19. In which direction is data passed in React by default?

A. From child to parent

B. From parent to child

C. Both ways simultaneously

D. Data cannot be passed in React

Answer:

B. From parent to child

Explanation:

In React, data is passed from parent to child through props by default. If you want to pass data from a child to a parent, you'd typically use callback functions.

20. What does a constructor method in a class-based React component do?

A. Render the component

B. Mount the component

C. Initialize the state and bind methods

D. Fetch data

Answer:

C. Initialize the state and bind methods

Explanation:

In a class-based React component, the constructor method is used to initialize the component's state and bind methods.

21. Which is the right way to bind a method in a React class component?

A. this.methodName = this.methodName.bind()

B. this.methodName.bind(this.methodName)

C. this.methodName.bind(this)

D. bind(this.methodName)

Answer:

C. this.methodName.bind(this)

Explanation:

In React class components, methods are bound using .bind(this) to ensure they have the correct context.

22. Which of the following is used to define a prop's type in a component?

A. PropTypes

B. PropTypeCheck

C. ReactTypes

D. TypeProps

Answer:

A. PropTypes

Explanation:

PropTypes is a library that helps in defining and validating the types of props in a component.

23. Which hook is used for memorizing expensive computations in React?

A. useEffect

B. useMemo

C. useCallback

D. useMemory

Answer:

B. useMemo

Explanation:

The useMemo hook is used to memorize the result of an expensive computation, ensuring it doesn't get recalculated on every render unless its dependencies change.

24. What does the useReducer hook do?

A. Reduces the size of your components

B. Helps to optimize the performance of your components

C. Manages state and actions in a similar way to Redux

D. Reduces the number of hooks you can use in a component

Answer:

C. Manages state and actions in a similar way to Redux

Explanation:

useReducer is a hook that provides a way to manage state and actions in your components, similar to how Redux works.

25. What is Context in React?

A. A global state management tool

B. A way to pass data through the component tree without passing props down manually

C. A set of developer tools for debugging React applications

D. An API for creating animations

Answer:

B. A way to pass data through the component tree without passing props down manually

Explanation:

Context provides a way to share values (data or functions) between components without having to pass props manually at every level.

26. What is the purpose of the key prop in React?

A. To unlock additional React features

B. To help React identify which items have changed in a list

C. To determine the component hierarchy

D. To specify a unique identifier for a component's state

Answer:

B. To help React identify which items have changed in a list

Explanation:

The key prop helps React identify and differentiate each item in a list and determine which elements may need to be re-rendered.

27. How do you create a functional component in React?

A. Using the createComponent function

B. Using a JavaScript function or ES6 arrow function

C. Using the render method

D. By extending the React.ComponentClass

Answer:

B. Using a JavaScript function or ES6 arrow function

Explanation:

A functional component is a simple JavaScript function or ES6 arrow function that returns JSX.

28. Which lifecycle method is called once the component has been rendered to the DOM?

A. componentDidRender()

B. componentWillMount()

C. componentHasMounted()

D. componentDidMount()

Answer:

D. componentDidMount()

Explanation:

The componentDidMount() lifecycle method is called once the component has been rendered to the DOM, making it a common place to fetch data or handle other side effects.

29. Which command can you use to create a new React app?

A. create-react-app my-app

B. npm start my-app

C. npm install react

D. react new-app my-app

Answer:

A. create-react-app my-app

Explanation:

The create-react-app tool allows developers to quickly create and set up a new React project.

30. Which of the following hooks is used to execute side effects, such as data fetching, in functional components?

A. useState()

B. useEffect()

C. useMemo()

D. useProps()

Answer:

B. useEffect()

Explanation:

The useEffect() hook is used to execute side effects in functional components, and it's often used for operations like data fetching, DOM manipulation, or setting up subscriptions.

31. What does JSX stand for?

A. JavaScript Extended

B. JavaScript XML

C. JavaScript Experience

D. Java Styled Components

Answer:

B. JavaScript XML

Explanation:

JSX stands for JavaScript XML. It allows developers to write HTML structures in a way that looks similar to XML within their JavaScript code, making the UI more intuitive and visually clear.

32. In which lifecycle method should you avoid setting state in a class component to prevent unnecessary re-renders?

A. shouldComponentUpdate()

B. componentDidUpdate()

C. componentWillUpdate()

D. render()

Answer:

D. render()

Explanation:

Calling setState() directly inside the render() method will lead to an infinite loop since render() will be called every time the state updates.

33. Which of the following hooks is used for sharing logic between components?

A. useContext()

B. useSharedLogic()

C. useCustomHook()

D. useCallback()

Answer:

C. useCustomHook()

Explanation:

Developers can create their own custom hooks (there's no actual hook named useCustomHook()) to share logic between different components. By convention, custom hooks start with the word "use".

34. How can you handle events in React?

A. By adding a native HTML event attribute to an element

B. By adding an inline JavaScript within HTML tags

C. By using synthetic event handlers provided by React

D. React does not support event handling

Answer:

C. By using synthetic event handlers provided by React

Explanation:

React wraps DOM events with its own set of events called synthetic events. These provide cross-browser consistency and integrate well with React's event system.

35. 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.

36. 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.

37. 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.

38. How do you handle form input changes in React?

A. Using the onChange event

B. Using the onInput attribute

C. Using the inputChanged method

D. Using the handleForm attribute

Answer:

A. Using the onChange event

Explanation:

In React, the onChange event is commonly used to detect when the value of an input element changes.

39. What is a controlled component in React?

A. A component that does not have any state

B. A component that dictates the behavior of other components

C. An input element whose value is controlled by React state

D. A component that cannot be updated

Answer:

C. An input element whose value is controlled by React state

Explanation:

A controlled component in React refers to an input element where the value is set by the component's state and can be altered via user interactions.

40. How do you prevent a form from submitting by default in React?

A. Using event.preventDefault()

B. Using stopSubmit()

C. Setting the form's submit attribute to false

D. Removing the action attribute from the form

Answer:

A. Using event.preventDefault()

Explanation:

In React's event handling system, event.preventDefault() is used to stop the default action of an event, like preventing a form from submitting to the server.