JavaScript Objective Questions and Answers - Set 3

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. This is part 3 of the series.

Practice JavaScript MCQs with Detailed Explanations

Answer at least 12 questions to submit and verify answers.

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