REACT JS MCQ Questions 100 MCQ

REACT JS MCQ Questions 100 MCQ. These 100 Multiple Choice Questions on React JavaScript will help you crack exams and interview at ease.

React Basics (MCQ 1 to 20)

Introduction to React

Question 1: What is React primarily used for?
A. To manage databases
B. To create dynamic user interfaces
C. To optimize server performance
D. To handle large datasets efficiently

   

Question 2: How is React different from other JavaScript frameworks like Angular and Vue?
A. React uses a real DOM
B. React uses a virtual DOM
C. React operates on a backend server
D. React doesn’t support component-based architecture

   

Question 3: What does the virtual DOM in React do?
A. It updates synchronously with the real DOM
B. It is a lightweight copy of the real DOM and updates asynchronously
C. It mirrors the real DOM in real-time
D. It is only used for server-side rendering

   

Question 4: Which of the following best describes JSX?
A. A JavaScript library
B. A syntax extension for writing HTML within JavaScript
C. A method for handling events
D. A way to style React components

   

JSX (JavaScript XML)

Question 5: What does JSX stand for?
A. JavaScript Extra
B. JavaScript XML
C. JavaScript Execution
D. JavaScript Extension

   

Question 6: How can you embed JavaScript expressions in JSX?
A. Using square brackets [ ]
B. Using double curly braces {{ }}
C. Using parentheses ( )
D. Using single curly braces { }

   

Question 7: Which of the following is an advantage of using JSX?
A. It allows for more efficient DOM manipulation
B. It provides better performance than JavaScript
C. It allows writing HTML elements directly inside JavaScript
D. It removes the need for JavaScript entirely

   

Components

Question 8: What is a functional component in React?
A. A class that returns HTML elements
B. A function that returns HTML elements using JSX
C. A method used to handle events
D. A class that manages state

   

Question 9: What is the primary difference between functional and class components in React?
A. Functional components can handle state
B. Class components can use lifecycle methods
C. Functional components can directly manipulate the DOM
D. Class components are stateless

   

Question 10: What are props in React used for?
A. To manage component lifecycle
B. To handle events in a component
C. To pass data between components
D. To manipulate the DOM

   

Question 11: Which method is required in a React class component?
A. render
B. componentDidMount
C. constructor
D. getDerivedStateFromProps

   

Question 12: What is the main purpose of state in a React component?
A. To pass data to child components
B. To manage dynamic data within a component
C. To define static properties
D. To handle user inputs

   

Events in React

Question 13: How does React handle events?
A. React uses the browser’s native event system
B. React uses its own synthetic event system
C. React handles events asynchronously
D. React does not support events

   

Question 14: Which of the following is an example of event binding in React?
A. onClick={this.handleClick.bind(this)}
B. onClick={this.handleClick()}
C. onClick=”this.handleClick()”
D. onclick={this.handleClick}

   

Question 15: How can you prevent the default behavior of an event in React?
A. Using stopPropagation()
B. Using event.preventDefault()
C. Using return false
D. Using a callback function

   

Question 16: What is event delegation in React?
A. Handling multiple events in one component
B. Handling events on the parent component instead of individual child elements
C. Using events to manipulate state
D. Using event listeners directly on child components

   

Question 17: Which of the following is the correct way to handle an event in React?
A. onClick=”handleClick()”
B. onClick={this.handleClick()}
C. onClick=”this.handleClick.bind(this)”
D. onClick={this.handleClick}

   

Question 18: How does React handle form inputs using events like onChange?
A. By using native browser events
B. By using a synthetic event system
C. By automatically updating the state
D. By binding the input value to the DOM

   

Question 19: Which of the following is a correct example of using the onChange event in React?
A. <input onChange=”handleChange()” />
B. <input onChange={this.handleChange()} />
C. <input onChange={this.handleChange} />
D. <input onChange=”this.handleChange” />

   

Question 20: How can you bind an event handler to ensure it has the correct ‘this’ context in class components?
A. By using this.methodName.bind(this) in the constructor
B. By using arrow functions inside the render method
C. By assigning the method to a variable
D. By using setState inside the method

   

React Advanced Concepts (MCQ 21 to 40)

State and Lifecycle

Question 21: What is the purpose of the state in React?
A. To store dynamic data that affects how the component renders
B. To pass data between components
C. To trigger events in the DOM
D. To define static variables for a component

   

Question 22: Which lifecycle method is called when a component is first rendered to the DOM?
A. componentDidMount
B. componentDidUpdate
C. componentWillUnmount
D. shouldComponentUpdate

   

Question 23: How do functional components manage state in React?
A. By using the useState hook
B. By using the this.state object
C. By directly modifying the DOM
D. By calling lifecycle methods

   

Question 24: What is the role of the componentWillUnmount lifecycle method?
A. To initialize state
B. To clean up resources before the component is unmounted
C. To handle side effects after rendering
D. To update the component state

   

Question 25: What is the correct syntax for updating state in a React class component?
A. this.state = { value: newValue }
B. this.setState({ value: newValue })
C. state = { value: newValue }
D. setState({ value: newValue })

   

React Hooks

Question 26: What is the useState hook used for in React?
A. To manage side effects in a functional component
B. To set and update the state in functional components
C. To handle lifecycle methods in class components
D. To manage props between components

   

Question 27: What does the useEffect hook allow you to do?
A. Handle side effects like data fetching or subscriptions
B. Manage local component state
C. Pass data to child components
D. Access the component lifecycle methods in class components

   

Question 28: Which of the following is a correct example of using the useState hook?
A. const [value, setValue] = setState(0);
B. const [value, setValue] = useState(0);
C. const [value, setValue] = state(0);
D. const [value, setValue] = updateState(0);

   

Question 29: What does the useContext hook allow you to do?
A. Access the global state across all components
B. Consume context values without prop drilling
C. Directly update the parent component’s state
D. Set initial state for functional components

   

Question 30: How does the useReducer hook differ from the useState hook?
A. useReducer is used for handling complex state logic, while useState is for simple state management
B. useReducer can only be used in class components
C. useReducer is for managing side effects
D. useState is asynchronous, but useReducer is synchronous

   

Context API

Question 31: What is the main purpose of the Context API in React?
A. To optimize component performance
B. To share global data across multiple components without prop drilling
C. To handle event propagation
D. To manage lifecycle methods

   

Question 32: How do you create a Context in React?
A. By using useState
B. By using React.createContext()
C. By using the useEffect hook
D. By defining a new component

   

Question 33: What is the main difference between Context API and Redux?
A. Context API is for managing global state, Redux is for styling components
B. Context API is built-in to React, while Redux is an external library
C. Redux uses the virtual DOM, while Context API doesn’t
D. Redux is synchronous, while Context API is asynchronous

   

Question 34: How do you consume values from a Context in functional components?
A. By using the useEffect hook
B. By using the useContext hook
C. By using the useState hook
D. By directly accessing the context object

   

Forms in React

Question 35: What is a controlled component in React?
A. A component that manages its own state
B. A component where form data is handled by the DOM
C. A component where form data is controlled by React through state
D. A component that updates asynchronously

   

Question 36: How do you handle form submission in React?
A. By using the submit event of the form
B. By manually updating the state
C. By preventing the default form behavior using event.preventDefault()
D. By using a synthetic event handler

   

Question 37: What is the key difference between controlled and uncontrolled components in React?
A. Controlled components are more performant
B. Uncontrolled components manage form data through the DOM, while controlled components manage it through React state
C. Controlled components do not need state
D. Uncontrolled components can directly modify props

   

Question 38: Which of the following is an example of a controlled component?
A. <input defaultValue=”text” />
B. <input value={this.state.value} onChange={this.handleChange} />
C. <input type=”submit” />
D. <input ref={inputRef} />

   

Question 39: How do you handle validation in forms in React?
A. By writing validation logic inside the onSubmit handler
B. By using the componentWillUpdate lifecycle method
C. By attaching validation to the form tag
D. By using context to pass validation rules

   

Question 40: Which of the following is an advantage of using controlled components in forms?
A. They allow for direct DOM manipulation
B. They make it easier to handle form validation and control user input
C. They reduce the need for event handling
D. They eliminate the need for state

   

Routing and Navigation (MCQ 41 to 50)

React Router

Question 41: What is React Router used for in a React application?
A. To manage component state
B. To handle navigation and routing between different components
C. To optimize performance
D. To fetch data from APIs

   

Question 42: How do you set up routing in a React application?
A. By importing and using the BrowserRouter, Route, and Switch components
B. By using a state variable to track routes
C. By writing custom functions to handle navigation
D. By embedding links inside components

   

Question 43: What is the purpose of the Switch component in React Router?
A. To load the styles for the active route
B. To group multiple routes and render only the first matching route
C. To manage global state between components
D. To switch between different components based on user inputs

   

Question 44: What is a common use case for route parameters in React Router?
A. To pass dynamic values through the URL
B. To store user data in local storage
C. To track user session information
D. To update the component state

   

Question 45: How do you define a route with a parameter in React Router?
A. <Route path=”/user/:id” component={UserComponent} />
B. <Route path=”/user?id” component={UserComponent} />
C. <Route param=”/user/:id” component={UserComponent} />
D. <Route query=”/user?id” component={UserComponent} />

Question 46: How do you access route parameters in a component?
A. Through the props object using props.match.params
B. By reading from local storage
C. By using the useState hook
D. Through the state object using state.params

   

Question 47: What is the purpose of the Link component in React Router?
A. To handle API requests
B. To create navigation links that update the URL without refreshing the page
C. To render a new component
D. To store data in session storage

   

Question 48: How can you redirect users programmatically in React Router?
A. By modifying the URL directly
B. By using the history object in combination with history.push()
C. By setting a new state value
D. By using the onClick event

   

Question 49: What is the purpose of the useHistory hook in React Router?
A. To manage state transitions
B. To give access to the history object for navigation purposes
C. To access route parameters
D. To handle form submissions

   

Question 50: How can you handle nested routes in React Router?
A. By using a single Route component
B. By placing child Route components inside a parent Route component
C. By defining routes in the state
D. By using the Link component inside each route

   

State Management (MCQ 51 to 60)

Introduction to Redux

Question 51: What is the main purpose of Redux in a React application?
A. To handle routing
B. To manage global state across the entire application
C. To handle form submissions
D. To manage local component styles

   

Question 52: Which of the following is a core concept of Redux?
A. Props and Context
B. State and Effects
C. Actions, Reducers, and Store
D. Components and Hooks

   

Question 53: What is an action in Redux?
A. A function that modifies the state directly
B. A plain JavaScript object that describes an event or change in state
C. A function that fetches data from an API
D. A method for rendering components

   

Question 54: What is the purpose of a reducer in Redux?
A. To fetch data from APIs
B. To update the component tree
C. To specify how the application’s state changes in response to an action
D. To dispatch actions to components

   

Question 55: How is the Redux store created in a React application?
A. By calling createStore and passing in the root reducer
B. By using useState
C. By importing the store from the component file
D. By setting state manually in the constructor

   

Redux with React

Question 56: How do you connect a React component to the Redux store?
A. By using the useState hook
B. By using the connect function from react-redux
C. By importing the store directly into the component
D. By using the setState function

   

Question 57: What does the mapStateToProps function do in Redux?
A. It dispatches actions to the store
B. It maps the state from the Redux store to the props of the component
C. It initializes the component’s state
D. It handles API calls in Redux

   

Question 58: What is the purpose of the mapDispatchToProps function in Redux?
A. To map component state to the store
B. To map action dispatchers to the component props
C. To handle side effects
D. To update the Redux store automatically

   

Question 59: Which of the following is a common use case for Redux middleware?
A. To manage component state
B. To handle asynchronous actions like API calls
C. To handle form validation
D. To manage routing in the application

   

Question 60: What does Redux Thunk allow you to do?
A. Write action creators that return functions instead of action objects
B. Manage routing in a React application
C. Render components conditionally
D. Fetch data from APIs synchronously

   

Error Handling and Debugging (MCQ 61 to 70)

Error Boundaries in React

Question 61: What are error boundaries in React used for?
A. To catch JavaScript errors in the entire application
B. To catch errors in a component’s child tree during rendering
C. To prevent re-rendering of a component
D. To handle routing errors

   

Question 62: Which lifecycle method is used to catch errors in an error boundary?
A. componentDidCatch
B. componentDidMount
C. componentWillUnmount
D. componentWillUpdate

   

Question 63: Can error boundaries catch errors in event handlers?
A. Yes, error boundaries catch all types of errors
B. No, error boundaries do not catch errors in event handlers
C. Only if the error handler is asynchronous
D. Only when combined with Redux

   

Question 64: What happens if an error boundary catches an error?
A. It silently logs the error and continues rendering
B. It displays a fallback UI instead of crashing the application
C. It automatically fixes the error
D. It stops the component from rendering and shows a warning

   

Handling Errors in Async Code

Question 65: What is the best way to handle errors in async code in React?
A. By using error boundaries
B. By wrapping async code in a try-catch block
C. By using componentWillUnmount
D. By preventing state updates

   

Question 66: How can you handle errors in Promises in React?
A. By adding error handling in componentDidMount
B. By using .catch() at the end of the Promise chain
C. By using preventDefault in the Promise
D. By updating the state with the error message

   

Debugging React Applications

Question 67: Which of the following tools is most commonly used for debugging React applications?
A. Chrome DevTools
B. Node.js
C. React Developer Tools
D. Redux DevTools

   

Question 68: How can you inspect the state and props of a React component during development?
A. By using the console.log method
B. By using the React Developer Tools
C. By directly accessing the component’s state in the DOM
D. By using componentDidCatch

   

Question 69: What does the profiler feature in React Developer Tools do?
A. It allows you to directly modify state values
B. It helps identify performance bottlenecks by recording renders and updates
C. It displays errors in your component tree
D. It tracks state changes in Redux

   

Question 70: How can you view performance optimizations or re-renders in React?
A. By using the console.log method
B. By using the performance tab in React Developer Tools
C. By using setState
D. By using the Network tab in Chrome DevTools

   

Performance Optimization (MCQ 71 to 80)

React Performance Techniques

Question 71: What is the purpose of memoization in React?
A. To increase the size of the DOM
B. To prevent unnecessary re-renders by caching the results of function calls
C. To automatically handle API requests
D. To simplify the component lifecycle

   

Question 72: Which hook in React can be used to memoize values?
A. useEffect
B. useState
C. useMemo
D. useContext

   

Question 73: What is the purpose of the useCallback hook?
A. To memoize function definitions and prevent them from being recreated on every render
B. To trigger a component re-render
C. To handle side effects in functional components
D. To update the state in class components

   

Question 74: How can React.memo help optimize component performance?
A. By preventing a component from re-rendering unless its props change
B. By preventing the component tree from updating
C. By automatically handling state updates
D. By preventing side effects in functional components

   

Question 75: What is the purpose of code splitting in React?
A. To load all JavaScript files at once
B. To load only the necessary JavaScript files when needed, improving load times
C. To merge CSS and JavaScript files
D. To prevent re-renders

   

Question 76: Which of the following methods can be used for lazy loading components in React?
A. useState
B. useEffect
C. React.lazy
D. React.memo

   

Question 77: How does the useMemo hook improve performance in React?
A. By memoizing values and preventing expensive recalculations on each render
B. By preventing component re-renders
C. By fetching data automatically
D. By handling lifecycle methods in functional components

   

Question 78: What is the purpose of the shouldComponentUpdate lifecycle method in class components?
A. To force a component to always update
B. To allow React to decide whether to re-render a component based on changes to props or state
C. To prevent state updates in a component
D. To handle form submissions

   

Question 79: What is the role of the React Profiler?
A. To track and visualize the performance of components in terms of rendering time
B. To store component data
C. To automatically fix performance issues
D. To handle error boundaries

   

Question 80: Which of the following is a way to fix memory leaks in React applications?
A. By clearing intervals and timeouts in the componentWillUnmount lifecycle method
B. By updating the state on each render
C. By using inline styles instead of CSS
D. By preventing the component from rendering

   

React with APIs (MCQ 81 to 90)

Fetching Data

Question 81: Which method is commonly used in React to fetch data from an API?
A. useState
B. fetch or Axios
C. useEffect
D. React.memo

   

Question 82: Where is the best place to fetch data in a React component?
A. Inside the render method
B. Inside a useEffect hook
C. Inside the constructor
D. Inside the event handler

   

Question 83: How can you handle asynchronous data fetching in React?
A. By using synchronous functions only
B. By using Promises or async/await inside useEffect
C. By directly manipulating the DOM
D. By using the useState hook alone

   

Question 84: What is the purpose of handling loading states when fetching data in React?
A. To prevent re-rendering
B. To display a loading indicator while waiting for the data
C. To automatically update the state
D. To cache the API response

   

Question 85: How do you handle errors when fetching data from an API in React?
A. By using try-catch blocks in async/await functions or .catch() in Promises
B. By ignoring the API call if it fails
C. By automatically retrying the API call
D. By wrapping the component with an error boundary

   

RESTful APIs

Question 86: Which HTTP methods are commonly used for CRUD operations in RESTful APIs?
A. GET, POST, PUT, DELETE
B. HEAD, PATCH, TRACE, OPTIONS
C. CONNECT, UPDATE, DELETE, FETCH
D. POST, GET, PATCH, UPDATE

   

Question 87: How can you perform a GET request in React using Axios?
A. axios.get(‘/url’)
B. fetch(‘/url’)
C. useEffect()
D. axios.post(‘/url’)

   

Question 88: What is the purpose of using async/await in API calls in React?
A. To handle synchronous operations
B. To make asynchronous code easier to write and read
C. To replace Promises entirely
D. To handle form validation

   

Question 89: What is the main advantage of using Axios over the fetch API in React?
A. Axios is synchronous by default
B. Axios automatically handles JSON responses and has a more user-friendly API
C. Axios only supports POST requests
D. Axios is a built-in feature of React

   

Question 90: How do you perform a POST request in React using the fetch API?
A. fetch(‘/url’, { method: ‘POST’, body: JSON.stringify(data) })
B. axios.post(‘/url’, data)
C. fetch(‘/url’)
D. axios.get(‘/url’, data)

   

Testing in React (MCQ 91 to 95)

Unit Testing React Components

Question 91: What is the purpose of unit testing in React?
A. To test the entire application as a whole
B. To test individual components in isolation
C. To test the performance of React applications
D. To handle asynchronous operations

   

Question 92: Which library is commonly used for testing React components?
A. Axios
B. Redux
C. Jest and React Testing Library
D. Mocha

   

Question 93: What is snapshot testing in React?
A. A type of testing that compares a rendered component’s output to a previously stored snapshot
B. A testing method that tracks state changes
C. A method of testing API requests
D. A tool for monitoring performance

   

Question 94: How can you mock API calls in unit tests for React components?
A. By making real API requests
B. By using Jest or other testing libraries to simulate API responses
C. By testing the API directly in the component
D. By calling the API in the constructor

   

Question 95: What is the primary advantage of using Jest for testing React applications?
A. Jest is faster than other testing tools
B. Jest has built-in support for mocking, snapshot testing, and easy configuration for React apps
C. Jest automatically generates tests for components
D. Jest is a feature of React itself

   

---

CSS in React (MCQ 96 to 100)

Styling Components in React

Question 96: What is CSS-in-JS in React?
A. A way to write JavaScript inside CSS files
B. A method for writing styles within JavaScript files using libraries like styled-components or Emotion
C. A way to include external CSS files in JavaScript
D. A feature that eliminates the need for styling in React

   

Question 97: Which of the following is a benefit of using CSS-in-JS in React?
A. It makes styles global across the application
B. It allows for scoped styles within components
C. It eliminates the need for state management
D. It only works in class components

   

Question 98: What is the difference between inline styles and external stylesheets in React?
A. Inline styles are written directly in the component’s JSX, while external stylesheets are stored separately and linked to the component
B. Inline styles perform better than external stylesheets
C. External stylesheets cannot be used in React components
D. Inline styles are only for functional components

   

Question 99: What are CSS modules in React?
A. A way to include JavaScript logic inside CSS files
B. A method for writing locally scoped CSS classes
C. A replacement for inline styles
D. A method for combining multiple CSS files into one

   

Question 100: Which of the following is a best practice when styling components in React?
A. Use inline styles for all components
B. Use globally scoped styles for better control
C. Use scoped or modular styles to prevent style conflicts across components
D. Avoid using external stylesheets

   

Read Also: Quantum Computing MCQs

Most Asked Questions on React JS