React Js MCQs with answers Page - 11

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. What does `React.StrictMode` do?

  • (A) Disables unused components
  • (B) Highlights potential problems in an application
  • (C) Automatically fixes bugs
  • (D) Prevents side effects
💬 Discuss
✅ Correct Answer: (B) Highlights potential problems in an application
Explanation: StrictMode is used to highlight potential issues in development mode.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What is a controlled component?

  • (A) A component that controls its own rendering
  • (B) A component that manages its own state
  • (C) A component whose form input values are controlled by React
  • (D) A component that is reused
💬 Discuss
✅ Correct Answer: (C) A component whose form input values are controlled by React
Explanation: Controlled components have form elements whose values are tied to React state.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What is the purpose of `useMemo`?

  • (A) To fetch data
  • (B) To optimize performance by memoizing values
  • (C) To watch props
  • (D) To render UI elements
💬 Discuss
✅ Correct Answer: (B) To optimize performance by memoizing values
Explanation: `useMemo` prevents unnecessary recalculations of values.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. Which is true about props in React?

  • (A) Props are immutable
  • (B) Props can only be strings
  • (C) Props change during component lifetime
  • (D) Props are optional
💬 Discuss
✅ Correct Answer: (A) Props are immutable
Explanation: Props are read-only and cannot be modified by the component receiving them.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What is the return type of a functional component?

  • (A) String
  • (B) HTML
  • (C) JSX
  • (D) Object
💬 Discuss
✅ Correct Answer: (C) JSX
Explanation: Functional components return JSX, which React converts to real DOM elements.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. How does React achieve better performance?

  • (A) By using AJAX
  • (B) By caching the DOM
  • (C) By using the virtual DOM and efficient diffing
  • (D) By using CSS-in-JS
💬 Discuss
✅ Correct Answer: (C) By using the virtual DOM and efficient diffing
Explanation: React uses a virtual DOM and diffing algorithm to minimize DOM updates.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What happens if you try to render an array in JSX?

  • (A) It throws an error
  • (B) Only the first element renders
  • (C) All elements render correctly
  • (D) It ignores the array
💬 Discuss
✅ Correct Answer: (C) All elements render correctly
Explanation: JSX can render arrays of elements as long as each has a unique key.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What does `defaultValue` do in input elements?

  • (A) It sets a static initial value
  • (B) It changes the state
  • (C) It disables the input
  • (D) It binds the input to state
💬 Discuss
✅ Correct Answer: (A) It sets a static initial value
Explanation: `defaultValue` sets the initial value for uncontrolled components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:16 pm in React Js

Q. What does JSX stand for in React?

  • (A) JavaScript and XML
  • (B) Java Syntax Extension
  • (C) JavaScript XML Structure
  • (D) JavaScript eXtension
💬 Discuss
✅ Correct Answer: (A) JavaScript and XML
Explanation: JSX stands for JavaScript and XML, allowing HTML to be written inside JavaScript.

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

Q. Which of the following is not a valid React hook?

  • (A) useReducer
  • (B) useState
  • (C) useClass
  • (D) useEffect
💬 Discuss
✅ Correct Answer: (C) useClass
Explanation: useClass is not a valid React hook.

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

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