JavaScript Objective Questions and Answers

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.

31

What will be logged? console.log(typeof undefined == typeof null);

Medium
32

Which pattern helps prevent memory leaks with event listeners?

High
33

What does Promise.all() do if one Promise rejects?

High
34

Which scenario creates a closure?

Medium
35

What is the output? console.log(+true);

Medium
36

Which statement about async/await is true?

High
37

What is the output? console.log([] === []);

Medium
38

Which structure is most likely to cause a memory leak?

High
39

What does the call stack manage?

Medium
40

Which operation is synchronous?

Medium
41

What will be logged? console.log(typeof function(){});

Medium
42

Which can prevent accidental global variables?

Medium
43

What happens if await is used outside async?

Medium
44

What is the output? console.log(null + 1);

Medium
45

Which tool helps avoid memory leaks in key-value storage?

High