React JS MCQs with answers Page - 23

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. How can you prevent a component from rendering in React?

  • (A) Return null from the render method or functional component
  • (B) Call event.preventDefault()
  • (C) Use componentDidMount lifecycle method
  • (D) Remove the component from the DOM manually

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Q. Which of these is NOT a valid way to create a React component?

  • (A) function MyComponent() { return <div />; }
  • (B) class MyComponent extends React.Component {}
  • (C) const MyComponent = () => <div />;
  • (D) createComponent(() => <div />);

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Q. What is the difference between controlled and uncontrolled components in React?

  • (A) Controlled components have their value controlled by React state, uncontrolled components manage their own state
  • (B) Controlled components are class components, uncontrolled are functional
  • (C) Controlled components do not have state, uncontrolled do
  • (D) There is no difference

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Q. How can you optimize performance by avoiding unnecessary re-renders in React?

  • (A) Use React.memo for functional components and shouldComponentUpdate for class components
  • (B) Avoid using props
  • (C) Disable JavaScript
  • (D) Use inline styles

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Q. What does the term 'prop drilling' mean in React?

  • (A) Passing props through many levels of components unnecessarily
  • (B) Drilling holes in the UI
  • (C) Using CSS selectors in props
  • (D) Deep cloning props

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Q. Which React feature helps avoid prop drilling?

  • (A) Context API
  • (B) useState
  • (C) useEffect
  • (D) Redux

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Q. What is the correct syntax to create a React Fragment?

  • (A) <> ... </>
  • (B) <fragment> ... </fragment>
  • (C) <React.Fragment> ... </React.Fragment>
  • (D) Both option1 and option3

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Q. What is the purpose of the useCallback hook?

  • (A) To memoize functions to prevent unnecessary re-creations
  • (B) To memoize values
  • (C) To manage state
  • (D) To fetch data

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Q. Which of the following is a feature of React?

  • (A) Virtual DOM
  • (B) Direct DOM manipulation
  • (C) Two-way data binding
  • (D) Server-side rendering only

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Q. What is the difference between useEffect and useLayoutEffect?

  • (A) useLayoutEffect fires synchronously after all DOM mutations, useEffect fires asynchronously after paint
  • (B) useEffect is only for class components
  • (C) useLayoutEffect is deprecated
  • (D) There is no difference

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