React Js MCQs with answers Page - 12

Dear candidates you will find MCQ questions of React Js here. Learn these questions and prepare yourself for coming examinations and interviews. You can check the right answer of any question by clicking on any option or by clicking view answer button.
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Q. Which attribute is used in React to give CSS classes?

  • (A) class
  • (B) className
  • (C) css
  • (D) styleName
💬 Discuss
✅ Correct Answer: (B) className
Explanation: In JSX, 'className' is used instead of 'class' to avoid conflicts with JavaScript reserved keywords.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. What is the main advantage of using keys in React lists?

  • (A) Faster search
  • (B) Easy sorting
  • (C) Helps React identify which items have changed
  • (D) Avoids duplicate rendering
💬 Discuss
✅ Correct Answer: (C) Helps React identify which items have changed
Explanation: Keys help React identify which items have changed, been added, or removed.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. Which method is used to change the state in a React class component?

  • (A) this.setChange()
  • (B) this.changeState()
  • (C) this.setState()
  • (D) this.updateState()
💬 Discuss
✅ Correct Answer: (C) this.setState()
Explanation: this.setState() is used to update the state in class components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. How many elements can a React component return?

  • (A) Only one element
  • (B) Only two elements
  • (C) Multiple elements using an array or fragment
  • (D) None
💬 Discuss
✅ Correct Answer: (C) Multiple elements using an array or fragment
Explanation: React components can return multiple elements using React fragments or arrays.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. Which of the following is used for performance optimization in React?

  • (A) React.delay()
  • (B) React.cache()
  • (C) React.memo()
  • (D) React.optimize()
💬 Discuss
✅ Correct Answer: (C) React.memo()
Explanation: React.memo() is used to prevent unnecessary re-renders of functional components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. How do you pass data from parent to child component in React?

  • (A) Using setState
  • (B) Using props
  • (C) Using refs
  • (D) Using context
💬 Discuss
✅ Correct Answer: (B) Using props
Explanation: Props are used to pass data from parent to child components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. What will `useEffect(() => {}, [])` do?

  • (A) Run after every render
  • (B) Run only once after the initial render
  • (C) Never run
  • (D) Run before every render
💬 Discuss
✅ Correct Answer: (B) Run only once after the initial render
Explanation: An empty dependency array means the effect runs only once after the initial render.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. Which hook is best for accessing DOM elements directly?

  • (A) useEffect
  • (B) useMemo
  • (C) useRef
  • (D) useState
💬 Discuss
✅ Correct Answer: (C) useRef
Explanation: useRef can be used to access DOM elements directly using ref.current.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. What is a React fragment?

  • (A) A single root element
  • (B) A placeholder for props
  • (C) A tool for debugging
  • (D) A way to group elements without extra nodes
💬 Discuss
✅ Correct Answer: (D) A way to group elements without extra nodes
Explanation: React fragments let you group multiple elements without adding extra nodes to the DOM.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

Q. Which React component lifecycle method is called before rendering?

  • (A) componentDidMount
  • (B) componentWillUnmount
  • (C) render
  • (D) getDerivedStateFromProps
💬 Discuss
✅ Correct Answer: (D) getDerivedStateFromProps
Explanation: getDerivedStateFromProps is called before render and helps update state based on props.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:17 pm in React Js

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