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Javascript MCQ With Answers

41 practice questions · Last updated on Aug 25, 2026

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JavaScript interviews concentrate on the parts of the language that behave unexpectedly. Expect closures, hoisting and the temporal dead zone, how the event loop orders microtasks and macrotasks, promises and async/await, prototypal inheritance, and how this is determined by the call site. Interviewers also test practical judgement around shallow versus deep copies, debouncing and throttling, and where to store an authentication token. The questions below cover the language fundamentals and the browser APIs that accompany them.

Javascript MCQ

1.What is the output of typeof null in JavaScript?

3.What is the difference between == and ===?

6.What is a closure?

7.How do arrow functions handle the this keyword?

8.What does Array.prototype.map() return?

9.Which method creates a deep copy handling Dates, Maps and circular references?

10.What is the temporal dead zone?

11.Which Promise combinator waits for all promises and reports each outcome, never rejecting?

12.What does the spread operator (...) do with an array?

13.What is event bubbling?

14.Which statement about hoisting is correct?

15.What does the reduce() method do?

16.How do you correctly check whether a value is NaN?

17.What is the difference between null and undefined?

18.Which of these correctly runs two async operations in parallel?

19.What does the async keyword do to a function?

20.What is event delegation?

22.What is the prototype chain?

23.What does the optional chaining operator ?. do?

24.What is the difference between the nullish coalescing operator (??) and the logical OR operator?

25.Which array method returns the first element satisfying a condition?

26.What is a JavaScript Map compared to a plain object?

27.What does 'use strict' do?

28.What is the difference between debounce and throttle?

29.Which storage mechanism is safest for an authentication token?

30.What does Array.prototype.slice() do?

31.What is the result of [1,2,3] + [4,5]?

32.What is a Promise in JavaScript?

33.What does the DOMContentLoaded event indicate?

34.What is the difference between function declarations and function expressions regarding hoisting?

35.What does JSON.stringify() do with a function property in an object?

36.Which of these creates a shallow copy of an object?

37.What is the purpose of the finally block in a try/catch/finally?

38.What does the every() array method return?

39.What is the main difference between localStorage and sessionStorage?

40.What does preventDefault() do on an event object?

41.In an ES module, which statement is true?

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