JavaScript MCQ Questions with answers and solutions Page 160

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Q. Which keyword prevents object modification?

(A) const
(B) Object.seal()
(C) Object.freeze()
(D) Object.prevent()

💬 Discuss

✅ Correct Answer: (C) Object.freeze()

Explanation: Object.freeze() prevents adding, removing, or modifying properties.

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Q. What is the result?

Code:

let a = [1,2,3];
a.length = 0;
console.log(a);

(A) []
(B) [1,2,3]
(C) undefined
(D) null

💬 Discuss

✅ Correct Answer: (A) []

Explanation: Setting length = 0 clears the array.

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Q. Which keyword is used to handle errors?

(A) handle
(B) try
(C) check
(D) error

💬 Discuss

✅ Correct Answer: (B) try

Explanation: The try...catch statement is used to handle errors.

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Q. What is the output?

Code:

let x = [1,2,3];
console.log(x instanceof Array);

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

💬 Discuss

✅ Correct Answer: (A) true

Explanation: Array is the constructor for arrays, so instanceof returns true.

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Q. What does the spread operator (...) do?

(A) Deletes properties
(B) Merges arrays or objects
(C) Freezes variables
(D) Compiles code

💬 Discuss

✅ Correct Answer: (B) Merges arrays or objects

Explanation: Spread syntax expands elements of iterable objects like arrays or objects.

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Q. What will this output?

Code:

let name = 'John';
console.log(`Hello ${name}`);

(A) Hello ${name}
(B) Hello name
(C) Hello John
(D) undefined

💬 Discuss

✅ Correct Answer: (C) Hello John

Explanation: Template literals use ${} to interpolate variables.

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Q. Which object method is used to get object keys?

(A) Object.getKeys()
(B) Object.keys()
(C) Object.values()
(D) Object.entries()

💬 Discuss

✅ Correct Answer: (B) Object.keys()

Explanation: Object.keys(obj) returns an array of a given object's keys.

JavaScript MCQs with answers Page - 160

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