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JavaScript Objective Questions and Answers

Practice JavaScript objective questions with answers and clear explanations. Covers core JavaScript, ES6+, closures, scope, hoisting, async programming, promises, event loop, prototypes, memory management, and advanced language concepts.

This JavaScript quiz contains carefully curated objective questions with correct answers and clear explanations. It is designed for frontend and backend developers, interview preparation, and deep understanding of modern JavaScript concepts including ES6+, asynchronous behavior, scope, closures, and performance pitfalls.

Practice JavaScript MCQs with Detailed Explanations

Answer at least 12 questions to submit.

16.
Which queue executes first in the event loop?
High
17.
What is the output? Promise.resolve(1) .then(x => x + 1) .then(x => { throw x; }) .catch(err => console.log(err));
High
18.
Which statement about prototypes is correct?
Medium
19.
What does this keyword refer to inside an arrow function?
Medium
20.
What is the output? console.log(typeof (() => {}));
Medium
21.
What will be the output order? console.log('A'); setTimeout(() => console.log('B')); Promise.resolve().then(() => console.log('C')); console.log('D');
High
22.
What is the output? async function test() { return 5; } console.log(test());
Medium
23.
What does await do internally?
High
24.
Which causes a memory leak in JavaScript?
High
25.
What is the output? let a = { x: 1 }; let b = a; a = null; console.log(b.x);
Medium
26.
Which comparison avoids type coercion?
Medium
27.
What will be logged? console.log(1 + '2' + 3);
Medium
28.
What is the output? console.log(true + false);
Medium
29.
Which object is responsible for garbage collection?
High
30.
What happens if a Promise is neither resolved nor rejected?
Medium
Answered: 0 / 15

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