1. What is React.js?
a) A JavaScript framework
b) A JavaScript library
c) A CSS preprocessor
d) A programming language
Answer: b) A JavaScript library
2. Which virtual DOM does React use?
a) Real DOM
b) Shadow DOM
c) Virtual DOM
d) Light DOM
Answer: c) Virtual DOM
3. What is JSX in React?
a) JavaScript Extension
b) JavaScript XML
c) JavaScript XML Extension
d) JavaScript Syntax eXtension
Answer: b) JavaScript XML
4. How can you create a React element?
a) React.createElement()
b) React.create()
c) React.makeElement()
d) React.newElement()
Answer: a) React.createElement()
5. What is the purpose of state in React?
a) To store properties for a component
b) To manage the rendering of a component
c) To store local component data that may change
d) To manage global application state
Answer: c) To store local component data that may change
6. What lifecycle method is invoked after a component is rendered for the first time?
a) componentDidMount()
b) componentWillMount()
c) componentWillUpdate()
d) componentDidUpdate()
Answer: a) componentDidMount()
7. How can you pass data from a parent component to a child component in React?
a) Using props
b) Using state
c) Using refs
d) Using context
Answer: a) Using props
8. Which method is used to change the state of a component in React?
a) setState()
b) changeState()
c) modifyState()
d) updateState()
Answer: a) setState()
9. What is the purpose of key in React lists?
a) To uniquely identify elements in a list
b) To set a specific order for list elements
c) To determine the length of the list
d) To specify the data type of the list elements
Answer: a) To uniquely identify elements in a list
10. What is the purpose of React fragments?
a) To group multiple elements without adding extra nodes to the DOM
b) To create shadow DOMs
c) To optimize rendering performance
d) To hide elements from the DOM
Answer: a) To group multiple elements without adding extra nodes to the DOM
11. What is the purpose of PropTypes in React?
a) To define the types of properties that a component can accept
b) To validate CSS properties in a component
c) To handle errors in a component
d) To define default values for component properties
Answer: a) To define the types of properties that a component can accept
12. How can you prevent the default behavior of an event in React?
a) event.preventDefault()
b) event.stopDefault()
c) event.stopPropagation()
d) event.cancelDefault()
Answer: a) event.preventDefault()
13. What is the purpose of React refs?
a) To reference DOM elements or React components directly
b) To prevent memory leaks in React applications
c) To handle routing in React applications
d) To optimize rendering performance
Answer: a) To reference DOM elements or React components directly
14. In React, what is the recommended way to fetch data from an API?
a) componentDidMount() using fetch()
b) componentWillMount() using fetch()
c) componentDidUpdate() using axios
d) render() using XMLHttpRequest
Answer: a) componentDidMount() using fetch()
15. What is a higher-order component (HOC) in React?
a) A component that renders other components
b) A function that takes a component and returns a new component with additional props
c) A component with high performance
d) A component with a higher rendering priority
Answer: b) A function that takes a component and returns a new component with additional props
16. What is Redux in React?
a) A state management library
b) A routing library
c) A testing library
d) A UI component library
Answer: a) A state management library
17. What is the purpose of mapStateToProps in React-Redux?
a) To map state properties to component props
b) To define the initial state of a component
c) To map dispatch actions to component props
d) To connect a component to the Redux store
Answer: a) To map state properties to component props
18. What is the purpose of mapDispatchToProps in React-Redux?
a) To map dispatch actions to component props
b) To map state properties to component props
c) To connect a component to the Redux store
d) To define the initial state of a component
Answer: a) To map dispatch actions to component props
19. What is the purpose of React Router?
a) To manage state in a React application
b) To handle routing in a React application
c) To create animations in a React application
d) To manage forms in a React application
Answer: b) To handle routing in a React application
20. What is the purpose of PureComponent in React?
a) To create pure functions in React
b) To optimize rendering performance of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: b) To optimize rendering performance of a component
21. What is the purpose of shouldComponentUpdate in React?
a) To determine if a component should be updated and re-rendered
b) To handle user input in a component
c) To define the initial state of a component
d) To update the state of a component
Answer: a) To determine if a component should be updated and re-rendered
22. What is the purpose of componentDidCatch in React?
a) To catch JavaScript errors in a component tree
b) To handle user input in a component
c) To define the initial state of a component
d) To update the state of a component
Answer: a) To catch JavaScript errors in a component tree
23. What is the purpose of forwardRef in React?
a) To create a reference to a DOM element
b) To pass props from a parent component to a child component
c) To create a reference to a functional component
d) To handle user input in a component
Answer: a) To create a reference to a DOM element
24. What is the purpose of useCallback in React?
a) To memoize functions and prevent unnecessary renders
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To memoize functions and prevent unnecessary renders
25. What is the purpose of useReducer in React?
a) To manage complex state logic in a component
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To manage complex state logic in a component
26. What is the purpose of useContext in React?
a) To access context values in a functional component
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To access context values in a functional component
27. What is the purpose of useImperativeHandle in React?
a) To customize the instance value that is exposed to parent components when using refs
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To customize the instance value that is exposed to parent components when using refs
28. What is the purpose of useMemo in React?
a) To memoize the result of a computation and prevent unnecessary renders
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To memoize the result of a computation and prevent unnecessary renders
29. What is the purpose of useLayoutEffect in React?
a) To perform side effects after the browser has painted
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To perform side effects after the browser has painted
30. What is the purpose of useEffect in React?
a) To perform side effects in a functional component
b) To update the state of a component
c) To handle user input in a component
d) To define the initial state of a component
Answer: a) To perform side effects in a functional component
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