React Js MCQ Questions with answers and solutions Page 26

Q. How can you force a re-render in a functional component?

(A) By updating state using useState hook
(B) By calling render() manually
(C) By refreshing the browser
(D) By modifying props directly

💬 Discuss

✅ Correct Answer: (A) By updating state using useState hook

Explanation: Changing state triggers a re-render.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:33 pm in React Js

Q. Which lifecycle method is called when a component is first added to the DOM in class components?

(A) componentDidMount
(B) componentWillUnmount
(C) shouldComponentUpdate
(D) render

💬 Discuss

✅ Correct Answer: (A) componentDidMount

Explanation: componentDidMount runs after the first render.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. How do you update the state in React functional components?

(A) Using the setter function returned by useState
(B) Directly assigning to the state variable
(C) Using this.setState()
(D) Using useEffect

💬 Discuss

✅ Correct Answer: (A) Using the setter function returned by useState

Explanation: useState returns a state variable and a function to update it.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. What is the use of the useCallback hook?

(A) To memoize functions to prevent unnecessary re-creation
(B) To store mutable values
(C) To fetch data from APIs
(D) To manage side effects

💬 Discuss

✅ Correct Answer: (A) To memoize functions to prevent unnecessary re-creation

Explanation: useCallback returns a memoized callback.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. How can you optimize performance in React when passing functions to child components?

(A) Use useCallback to memoize the functions
(B) Define functions inside the render method
(C) Use inline functions in JSX
(D) Avoid using functions in props

💬 Discuss

✅ Correct Answer: (A) Use useCallback to memoize the functions

Explanation: Memoizing functions prevents unnecessary re-renders.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. What is the purpose of keys in React lists?

(A) They help React identify which items have changed, are added, or removed
(B) They set the HTML id attribute
(C) They are used for CSS styling
(D) They are required for accessibility

💬 Discuss

✅ Correct Answer: (A) They help React identify which items have changed, are added, or removed

Explanation: Keys improve React's reconciliation performance.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. What does the ReactDOM.render() method do?

(A) Renders React elements into the DOM
(B) Creates new React components
(C) Updates the virtual DOM
(D) Fetches data from a server

💬 Discuss

✅ Correct Answer: (A) Renders React elements into the DOM

Explanation: ReactDOM.render attaches React components to DOM nodes.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. How do you create a controlled component in React?

(A) By managing form input values in React state
(B) By using uncontrolled form inputs
(C) By directly modifying the DOM input value
(D) By using refs only

💬 Discuss

✅ Correct Answer: (A) By managing form input values in React state

Explanation: Controlled components have their state managed by React.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. What is the role of the Context API in React?

(A) To provide a way to pass data through the component tree without props
(B) To handle routing
(C) To style components
(D) To fetch data from APIs

💬 Discuss

✅ Correct Answer: (A) To provide a way to pass data through the component tree without props

Explanation: Context API helps avoid prop drilling.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

Q. Which of the following hooks is used to manage state in functional components?

(A) useState
(B) useEffect
(C) useContext
(D) useRef

💬 Discuss

✅ Correct Answer: (A) useState

Explanation: useState allows adding state to functional components.

Published by Mr. Dubey ⭐ 111.54K Points at 08-Jun-2025 03:59 pm in React Js

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