Top 100+ Most Asked Javascript Interview Questions

Comprehensive collection of the most frequently asked JavaScript interview questions covering fundamentals, ES6+, async programming, DOM manipulation, objects, arrays, functions, and advanced concepts. Each answer is concise, detailed, and interview-ready.

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1.What is event bubbling in JavaScript?

2.Explain bind, call and apply methods in JavaScript

3.What is the difference between map and forEach?

4.What is hoisting in JavaScript?

5.What is the difference between bind and call?

6.What is the 'this' keyword in JavaScript?

7.What is a callback function?

8.What is callback hell?

9.What is the difference between callback, promise, and async-await?

10.Explain async-await and its advantages

11.What is a closure in JavaScript?

12.What is currying in JavaScript?

13.What is a memory leak in JavaScript?

14.Explain the internal working mechanism of JavaScript

15.What is lexical scope?

16.Explain different Promise methods and when to use them

17.What are the different ways to create objects in JavaScript?

18.What are design patterns and how do you implement them?

19.What is a higher-order function?

20.What is an event emitter and how to use it?

21.What is a prototype in JavaScript?

22.What is CORS and why is it important?

23.What is the return value of the reduce method?

24.Does JavaScript have a Map data type?

25.How do you use Object-Oriented Programming in JavaScript?

26.What is Functional Programming in JavaScript?

27.What is the difference between for loop and array.map?

28.Explain JavaScript execution stack and event loop

29.What is middleware and where is it used?

30.What are array methods like some and every?

31.What is destructuring in JavaScript?

32.What is the spread operator?

33.What is the difference between undefined and null?

34.What are template literals in JavaScript?

35.Why is Node.js single-threaded?

36.What are shallow cloning and deep cloning?

37.What is the difference between require and import?

38.What is event capturing in JavaScript?

39.What is the difference between Object.freeze and Object.seal?

40.How does the const keyword work with objects?

41.Can values be added to const arrays?

42.What is the Singleton design pattern?

43.What distinguishes arrow functions from regular functions?

44.What are ES6 features?

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

46.What is the event loop?

47.What is event delegation?

48.What is debouncing in JavaScript?

49.What is throttling in JavaScript?

50.What is memoization?

51.What is Promise.all()?

52.What is deep equality?

53.What is Array.prototype.reduce()?

54.How do you flatten arrays?

55.How do you merge objects and arrays?

56.What is getElementsByClassName?

57.What is the difference between var, let, and const?

58.What is strict mode?

59.What is the Document Object Model (DOM)?

60.What is the difference between innerHTML and innerText?

61.What is the difference between window and document objects?

62.What is the Browser Object Model (BOM)?

63.What are cookies, localStorage, and sessionStorage?

64.What is the difference between synchronous and asynchronous?

65.What is AJAX?

66.What is the difference between XMLHttpRequest and fetch()?

67.What are JavaScript data types?

68.How do you iterate over objects and arrays?

69.What is the difference between Map and plain objects?

70.What is the difference between Map/Set and WeakMap/WeakSet?

71.What is prototypal inheritance?

72.What is the difference between function declarations and expressions?

73.What is an Immediately Invoked Function Expression (IIFE)?

74.What is the rest parameter?

75.What is the difference between parameters and arguments?

76.What are default parameters?

77.What is function scope and block scope?

78.What is the temporal dead zone?

79.What is a generator function?

80.What is the difference between slice and splice?

81.What are the differences between for, forEach, and map?

82.What is the filter method?

83.What is the find method?

84.What is the difference between findIndex and indexOf?

85.What is the includes method?

86.What is method chaining?

87.What is a pure function?

88.What are side effects in JavaScript?

89.What is immutability?

90.What is composition in JavaScript?

91.What is the difference between mouseenter and mouseover?

92.What is preventDefault and stopPropagation?

93.What is the typeof operator?

94.What is the instanceof operator?

95.What is NaN and how do you check for it?

96.What is type coercion?

97.What are truthy and falsy values?

98.What is the ternary operator?

99.What is optional chaining?

100.What is nullish coalescing?

101.What are logical operators beyond AND, OR, NOT?

102.What is Symbol in JavaScript?

103.What is BigInt?

104.What are WeakMap and WeakSet use cases?

105.What is the Proxy object?

106.What is the Reflect API?

107.What are JavaScript accessors (getters and setters)?

108.What are the differences between mutable and immutable objects?