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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.

46.
What does setTimeout(fn, 0) guarantee?
High
47.
Which is NOT a primitive type?
Medium
48.
What will be logged? console.log(typeof []);
Medium
49.
Which scenario causes callback hell?
Medium
50.
What is the output? console.log('5' - 2);
Medium
51.
Which causes implicit type coercion?
Medium
52.
What will be logged? console.log(Promise.resolve() === Promise.resolve());
High
53.
Which avoids blocking the UI thread?
High
54.
What happens when an exception is thrown inside async?
High
55.
Which prevents prototype pollution?
High
56.
What will be logged? console.log(typeof class A {});
Medium
57.
Which pattern reduces memory usage?
High
58.
What is the output? console.log(+'');
Medium
59.
Which structure allows garbage collection of keys?
High
60.
Why should deep cloning be handled carefully in JavaScript?
High
Answered: 0 / 15

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