Latest React JS Interview Questions & Answer for 2024
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Here are some latest React Js interview questions and answers to help you prepare:
1. What is JSX in React?
1. A JavaScript library
2. A syntax extension for JavaScript
3. A CSS preprocessor
4. A database
Answer: 2
2. What is the virtual DOM in React?
1. A copy of the real DOM
2. An exact replica of the DOM
3. A lightweight representation of the real DOM
4. None of the above
Answer: 3
3. How do you create a component in React?
1. Using HTML tags
2. Using a function or a class
3. Using CSS
4. Using a database
Answer: 2
4. What are props in React?
1. Properties used to pass data between components
2. A type of component
3. A way to style components
4. A debugging tool
Answer: 1
5. What is the purpose of the `key` prop in React?
1. To style elements
2. To uniquely identify elements in an array
3. To trigger re-renders
4. To bind event listeners
Answer: 2
6. What is a higher-order component (HOC) in React?
1. A component that renders higher on the page
2. A component that manages state
3. A function that takes a component and returns a new component
4. A way to fetch data from APIs
Answer: 3
7. What is the use of the `useState` hook in React?
1. To fetch data from APIs
2. To manage local component state
3. To apply styles
4. To handle events
Answer: 2
8. What does the `useEffect` hook do in React?
1. Applies styles to components
2. Manages side effects like data fetching
3. Handles form validation
4. Creates custom hooks
Answer: 2
9. How do you handle forms in React?
1. Using jQuery
2. Using controlled or uncontrolled components
3. Using CSS
4. Using local storage
Answer: 2
10. What is Redux used for in React applications?
1. Styling components
2. Managing state
3. Fetching data
4. Routing
Answer: 2
11. What is the Context API in React?
1. A state management tool
2. A way to manage global state
3. A method for styling components
4. A way to optimize performance
Answer: 2
12. What are React portals used for?
1. To create animations
2. To render children into a different part of the DOM
3. To fetch data
4. To handle events
Answer: 2
13. What is server-side rendering (SSR) in React?
1. Rendering the initial HTML on the server
2. Rendering the initial HTML on the client
3. Using server components
4. Using client components
Answer: 1
14. What is React Router used for?
1. Managing state
2. Managing routes in single-page applications
3. Fetching data
4. Styling components
Answer: 2
15. How do you optimize performance in React applications?
1. Using `useCallback` and `useMemo` hooks
2. Using CSS preprocessors
3. Using inline styles
4. Using local storage
Answer: 1
16. What is the primary benefit of the virtual DOM?
1. Eliminates the need for the actual DOM
2. Completely eliminates re-renders
3. Reduces updates to the actual DOM
4. Reduces API fetch times
Answer: 3
17. What is a React fragment?
1. A way to fetch data
2. A way to return multiple elements without a wrapper node
3. A method for state management
4. A CSS tool
Answer: 2
18. What is lazy loading in React?
1. Loading components asynchronously
2. Loading styles asynchronously
3. Fetching data lazily
4. Managing state lazily
Answer: 1
19. What are controlled components in React forms?
1. Components that control their own state
2. Components where form data is handled by the DOM
3. Components that handle data through state
4. Components with no state
Answer: 3
20. How do you handle errors in React?
1. Using error boundaries
2. Using try-catch in render methods
3. Using CSS for error handling
4. Using `useState` for errors
Answer: 1
21. What is the difference between `componentDidMount` and `componentDidUpdate`?
1. Both are used for data fetching
2. `componentDidMount` runs after initial render, `componentDidUpdate` runs after updates
3. Both run after every render
4. Both are deprecated
Answer: 2
22. What is the purpose of the `useRef` hook in React?
1. To manage state
2. To create mutable object references
3. To fetch data
4. To apply styles
Answer: 2
23. What does the `setState` method do?
1. Directly mutates the state
2. Schedules an update to the component's state
3. Fetches data
4. Applies styles
Answer: 2
24. What are synthetic events in React?
1. Native browser events
2. Cross-browser wrapper of native events
3. Custom user-defined events
4. Deprecated event system
Answer: 2
25. What is `React.createElement` used for?
1. Creating DOM elements
2. Creating React elements
3. Fetching data
4. Applying styles
Answer: 2
26. What are stateful components?
1. Components with no state
2. Components that manage their own state
3. Components that manage global state
4. Components that fetch data
Answer: 2
27. What is the difference between props and state?
1. Both are mutable
2. Props are read-only, state is mutable
3. State is read-only, props are mutable
4. Both are immutable
Answer: 2
28. What are refs used for in React?
1. Storing mutable data
2. Fetching data
3. Styling components
4. Handling events
Answer: 1
29. What is the `render` method in React?
1. Method to render components
2. Method to fetch data
3. Method to apply styles
4. Method to handle events
Answer: 1
30. What is `PropTypes` in React?
1. A library for managing state
2. A library for type-checking props
3. A CSS tool
4. A debugging tool
Answer: 2
31. What is the `useReducer` hook used for?
1. Fetching data
2. Managing complex state logic
3. Styling components
4. Handling events
Answer: 2
32. What is a pure component in React?
1. A component that fetches data
2. A component that prevents unnecessary re-renders
3. A component that manages state
4. A component that applies styles
Answer: 2
33. What is ReactDOM?
1. A CSS library
2. A library for rendering React components to the DOM
3. A state management tool
4. A data fetching library
Answer: 2
34. What is a memoized component in React?
1. A component that always re-renders
2. A component wrapped with `React.memo` to prevent unnecessary re-renders
3. A component that manages global state
4. A component that handles side effects
Answer: 2
35. What is the purpose of the `defaultProps` property in React?
1. To define default values for props
2. To define global state
3. To apply styles
4. To fetch data
Answer: 1
36. How do you handle routing in a React application?
1. Using the `context` API
2. Using the `useState` hook
3. Using `React Router`
4. Using `Redux`
Answer: 3
37. What does `shouldComponentUpdate` do?
1. Forces the component to re-render
2. Determines if the component should re-render
3. Handles side effects
4. Fetches data
Answer: 2
38. How do you handle asynchronous operations in React?
1. Using `fetch` or `axios` with `useEffect`
2. Using `setInterval`
3. Using CSS
4. Using synchronous functions
Answer: 1
39. What is the difference between `React.Component` and `React.PureComponent`?
1. `React.Component` implements `shouldComponentUpdate` by default
2. `React.PureComponent` implements `shouldComponentUpdate` with shallow prop and state comparison
3. `React.Component` does not support state
4. `React.PureComponent` is deprecated
Answer: 2
40. What is the role of the `render` method in class components?
1. To apply styles
2. To return the component's HTML
3. To handle events
4. To manage state
Answer: 2
41. What does `componentWillUnmount` do in React?
1. Handles side effects
2. Cleans up before the component is removed from the DOM
3. Renders the component
4. Fetches data
Answer: 2
42. What is a React hook?
1. A way to manage CSS in JS
2. Functions that let you use state and other React features in functional components
3. A new type of component
4. A debugging tool
Answer: 2
43. What is the purpose of the `useCallback` hook?
1. To fetch data
2. To memoize functions and prevent unnecessary re-renders
3. To apply styles
4. To manage state
Answer: 2
44. How do you pass data between React components?
1. Using CSS
2. Using local storage
3. Using props
4. Using the DOM
Answer: 3
45. What is the purpose of `React.StrictMode`?
1. To apply strict CSS rules
2. To highlight potential problems in an application
3. To fetch data strictly
4. To manage state strictly
Answer: 2
46. What does `useEffect` with an empty dependency array `[]` do?
1. Runs the effect after every render
2. Runs the effect only once after the initial render
3. Prevents the effect from running
4. Causes an error
Answer: 2
47. How do you create a context in React?
1. Using `React.createElement`
2. Using `React.createContext`
3. Using `React.useEffect`
4. Using `React.createRef`
Answer: 2
48. What is the difference between `useState` and `useReducer`?
1. `useState` is used for complex state logic, `useReducer` for simple state logic
2. `useState` is used for simple state logic, `useReducer` for complex state logic
3. Both are used for the same purpose
4. Both are deprecated
Answer: 2
49. What does `componentDidCatch` do in React?
1. Handles events
2. Catches errors in components
3. Fetches data
4. Applies styles
Answer: 2
50. What is the primary benefit of React's component-based architecture?
1. Easier styling
2. Code reusability and maintainability
3. Faster data fetching
4. Improved security
Answer: 2
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