React JS MCQs with answers Page - 9

Here, you will find a collection of MCQ questions on React JS. Go through these questions to enhance your preparation for upcoming examinations and interviews.

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Q. Which React feature helps break the UI into independent pieces?

  • (A) Fragments
  • (B) Components
  • (C) Hooks
  • (D) Keys

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Q. What is a React Fragment used for?

  • (A) To return multiple elements without a wrapper
  • (B) To create reusable logic
  • (C) To import multiple files
  • (D) To define state

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Q. Which of the following is true about useRef?

  • (A) It causes re-render on change
  • (B) It preserves a mutable reference
  • (C) It creates a new state
  • (D) It is used for performance optimization only

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Q. What is the difference between useMemo and useCallback?

  • (A) useMemo memoizes functions, useCallback memoizes values
  • (B) useCallback is used for memoizing values
  • (C) useMemo memoizes values, useCallback memoizes functions
  • (D) They do the same thing

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Q. Which one is a correct way to create a functional component?

  • (A) function MyComponent() {}
  • (B) class MyComponent extends Component {}
  • (C) component MyComponent = () => {}
  • (D) def MyComponent() {}

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Q. What is the correct syntax to pass a function as a prop?

  • (A) <MyComp func='doSomething' />
  • (B) <MyComp func={doSomething} />
  • (C) <MyComp func={doSomething()} />
  • (D) <MyComp func=doSomething />

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Q. Which hook allows you to share logic between components?

  • (A) useShared
  • (B) useGlobal
  • (C) Custom Hooks
  • (D) useEffect

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Q. Which attribute is required when using map to render lists?

  • (A) ref
  • (B) name
  • (C) key
  • (D) id

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Q. What is the default behavior of React's `useEffect` without a dependency array?

  • (A) It runs only once
  • (B) It runs on every render
  • (C) It runs only on component unmount
  • (D) It never runs

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Q. What does `ReactDOM.render()` do?

  • (A) It defines a React component
  • (B) It adds props to components
  • (C) It renders a React element into the DOM
  • (D) It creates a virtual DOM

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