JavaScript MCQ Questions with answers and solutions Page 153

Q. Which one will return 'true'?

Code:

console.log([] == ![]);

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

💬 Discuss

✅ Correct Answer: (A) true

Explanation: [] is truthy, so ![] is false. [] == false evaluates to true due to coercion.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. Which of the following creates a new array with results of calling a function on every element?

(A) map()
(B) filter()
(C) forEach()
(D) every()

💬 Discuss

✅ Correct Answer: (A) map()

Explanation: map() returns a new array after applying a function to each element.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. What will be logged?

Code:

console.log('2' - '1');

(A) 1
(B) 11
(C) NaN
(D) Error

💬 Discuss

✅ Correct Answer: (A) 1

Explanation: The - operator coerces both strings to numbers.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. How can you prevent a default event action in JavaScript?

(A) event.block()
(B) event.preventDefault()
(C) event.stop()
(D) event.cancel()

💬 Discuss

✅ Correct Answer: (B) event.preventDefault()

Explanation: event.preventDefault() stops the default behavior of an event.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. What is the output?

Code:

console.log(typeof []);

(A) object
(B) array
(C) list
(D) undefined

💬 Discuss

✅ Correct Answer: (A) object

Explanation: Arrays are technically objects in JavaScript.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. What will this return?

Code:

[1, 2, 3].reduce((a, b) => a + b);

(A) 6
(B) 1
(C) [1, 2, 3]
(D) Error

💬 Discuss

✅ Correct Answer: (A) 6

Explanation: reduce sums the elements: 1 + 2 + 3 = 6.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:39 am in JavaScript

Q. What does the following return?

Code:

console.log(typeof null);

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

💬 Discuss

✅ Correct Answer: (B) object

Explanation: typeof null returns 'object' due to a historical bug in JavaScript.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:40 am in JavaScript

Q. Which of these is not a looping structure in JavaScript?

(A) for
(B) foreach
(C) while
(D) do...while

💬 Discuss

✅ Correct Answer: (B) foreach

Explanation: JavaScript has forEach (as a method), not a foreach loop structure.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:40 am in JavaScript

Q. What will the code output?

Code:

console.log([] + []);

(A) []
(B) undefined
(C) NaN
(D) ""

💬 Discuss

✅ Correct Answer: (D) ""

Explanation: [] + [] results in an empty string because both are coerced to strings.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:40 am in JavaScript

Q. What is the purpose of the isNaN() function?

(A) Checks if a value is NaN
(B) Checks if a value is not a number
(C) Checks if a value is null
(D) Both a and b

💬 Discuss

✅ Correct Answer: (D) Both a and b

Explanation: isNaN() returns true if the value is NaN or not a number.

Published by Chandani ⭐ 10.97K Points at 14-Jun-2025 07:40 am in JavaScript

JavaScript MCQs with answers Page - 153

Q. Which one will return 'true'?

Q. Which of the following creates a new array with results of calling a function on every element?

Q. What will be logged?

Q. How can you prevent a default event action in JavaScript?

Q. What is the output?

Q. What will this return?

Q. What does the following return?

Q. Which of these is not a looping structure in JavaScript?

Q. What will the code output?

Q. What is the purpose of the isNaN() function?

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