React Js MCQ Questions with answers and solutions Page 9

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

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

💬 Discuss

✅ Correct Answer: (B) Components

Explanation: React uses components to encapsulate and reuse UI pieces.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

💬 Discuss

✅ Correct Answer: (A) To return multiple elements without a wrapper

Explanation: Fragments allow grouping elements without adding extra nodes to the DOM.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

💬 Discuss

✅ Correct Answer: (B) It preserves a mutable reference

Explanation: useRef keeps a persistent mutable value that does not cause re-render when updated.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

💬 Discuss

✅ Correct Answer: (C) useMemo memoizes values, useCallback memoizes functions

Explanation: useMemo is for expensive value computations; useCallback is for memoizing functions.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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() {}

💬 Discuss

✅ Correct Answer: (A) function MyComponent() {}

Explanation: Functional components are created using JavaScript functions.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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 />

💬 Discuss

✅ Correct Answer: (B) <MyComp func={doSomething} />

Explanation: Functions are passed as props using curly braces without invoking them.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

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

💬 Discuss

✅ Correct Answer: (C) Custom Hooks

Explanation: Custom hooks let you reuse stateful logic across components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

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

💬 Discuss

✅ Correct Answer: (C) key

Explanation: The key prop helps React identify individual items in lists efficiently.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:15 pm in React Js

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

💬 Discuss

✅ Correct Answer: (B) It runs on every render

Explanation: Without a dependency array, useEffect runs after every render.

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

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

💬 Discuss

✅ Correct Answer: (C) It renders a React element into the DOM

Explanation: `ReactDOM.render()` mounts a React component to a specific DOM node.

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

React Js MCQs with answers Page - 9

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

Q. What is a React Fragment used for?

Q. Which of the following is true about useRef?

Q. What is the difference between useMemo and useCallback?

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

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

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

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

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

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

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