JavaScript MCQ Questions with answers and solutions Page 159

Q. What is the output?

Code:

console.log('5' === 5);

(A) true
(B) false
(C) undefined
(D) Error

💬 Discuss

✅ Correct Answer: (B) false

Explanation: Triple equals (===) checks both value and type; string !== number.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. Which method is used to add elements at the beginning of an array?

(A) push()
(B) unshift()
(C) shift()
(D) concat()

💬 Discuss

✅ Correct Answer: (B) unshift()

Explanation: unshift() adds elements to the beginning of an array.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What will the following return?

Code:

console.log(typeof null);

(A) null
(B) object
(C) undefined
(D) function

💬 Discuss

✅ Correct Answer: (B) object

Explanation: typeof null returns 'object' (a long-standing bug in JS).

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. Which of these is not a primitive data type?

(A) String
(B) Number
(C) Boolean
(D) Object

💬 Discuss

✅ Correct Answer: (D) Object

Explanation: Object is not a primitive; it's a complex data type.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What is the result?

Code:

console.log(0 === -0);

(A) true
(B) false
(C) TypeError
(D) undefined

💬 Discuss

✅ Correct Answer: (A) true

Explanation: 0 and -0 are considered equal in strict comparison.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What is returned by JSON.parse('true')?

(A) true
(B) 'true'
(C) SyntaxError
(D) undefined

💬 Discuss

✅ Correct Answer: (A) true

Explanation: JSON.parse can parse valid JSON values, including booleans.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What will be the output?

Code:

console.log(!!0);

(A) true
(B) false
(C) 0
(D) undefined

💬 Discuss

✅ Correct Answer: (B) false

Explanation: 0 is falsy, so !!0 results in false.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. Which function executes a function after a specified time?

(A) setInterval()
(B) clearTimeout()
(C) setTimeout()
(D) delay()

💬 Discuss

✅ Correct Answer: (C) setTimeout()

Explanation: setTimeout() executes a function once after the delay.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What does isNaN('hello') return?

(A) true
(B) false
(C) NaN
(D) undefined

💬 Discuss

✅ Correct Answer: (A) true

Explanation: isNaN('hello') returns true because 'hello' is not a number.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

Q. What is the default scope of variables declared with var?

(A) Block
(B) Function
(C) Global
(D) Module

💬 Discuss

✅ Correct Answer: (B) Function

Explanation: Variables declared with var are function-scoped.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:41 am in JavaScript

JavaScript MCQs with answers Page - 159

Q. What is the output?

Q. Which method is used to add elements at the beginning of an array?

Q. What will the following return?

Q. Which of these is not a primitive data type?

Q. What is the result?

Q. What is returned by JSON.parse('true')?

Q. What will be the output?

Q. Which function executes a function after a specified time?

Q. What does isNaN('hello') return?

Q. What is the default scope of variables declared with var?

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