100 JavaScript Interview Questions !!

1. Beginner-Level JavaScript Questions

   1. What is JavaScript, and how is it different from Java?

   2. How do you declare a variable in JavaScript?

   3. What are the different ways to define a function in JavaScript?

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

   5. What are JavaScript data types?

   6. What is type coercion in JavaScript?

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

   8. What are truthy and falsy values in JavaScript?

   9. What is an array, and how do you create one in JavaScript?

   10. How do you loop through an array in JavaScript?

   11. What is the difference between null and undefined?

   12. How do you check if a variable is an array in JavaScript?

   13. What is the difference between slice() and splice()?

   14. What are template literals in JavaScript?

   15. How do you convert a string to a number in JavaScript?

   16. What is the difference between push() and pop()?

   17. What is the difference between unshift() and shift()?

   18. What is the purpose of the typeof operator?

   19. What is a JavaScript object?

   20. How do you access object properties?

Intermediate-Level JavaScript Questions

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

22. What is an arrow function?

23. What is a callback function?

24. What is the difference between synchronous and asynchronous code?

25. What is the event loop in JavaScript?

26. What is a closure in JavaScript?

27. How do you clone an object in JavaScript?

28. What is the difference between forEach(), map(), filter(), and reduce()?

29. What are JavaScript promises?

30. What are async/await functions?

31. What is the difference between localStorage, sessionStorage, and cookies?

32. How does prototypal inheritance work in JavaScript?

33. What is the this keyword in JavaScript?

34. How do you bind this in JavaScript?

35. What is the call(), apply(), and bind() method in JavaScript?

36. How do you handle errors in JavaScript using try...catch?

37. What are JavaScript modules, and how do you use them?

38. What is destructuring in JavaScript?

39. What is the spread/rest operator?

40. What is hoisting in JavaScript?

Advanced-Level JavaScript Questions

41. What is the difference between deep copy and shallow copy?

42. How does the JavaScript execution context work?

43. What is a higher-order function?

44. What are generators in JavaScript?

45. What are WeakMap and WeakSet in JavaScript?

46. What are ES6 classes, and how do they work?

47. How does the new keyword work in JavaScript?

48. What are getters and setters in JavaScript?

49. What is the difference between mutable and immutable objects?

50. How does event delegation work?

51. What is function currying in JavaScript?

52. What are Symbols in JavaScript?

53. How do you optimize performance in JavaScript?

54. What is the difference between setTimeout() and setInterval()?

55. What are microtasks and macrotasks in JavaScript?

56. How does debouncing and throttling work in JavaScript?

57. What is memoization in JavaScript?

58. How do you create a singleton pattern in JavaScript?

59. What is tail call optimization?

60. What are JavaScript proxies?

JavaScript DOM & Event Questions

61. What is the DOM in JavaScript?

62. How do you select elements in JavaScript?

63. What is the difference between innerHTML, innerText, and textContent?

64. How do you create and append elements to the DOM?

65. What is event bubbling and event capturing?

66. How do you stop event propagation in JavaScript?

67. What are event listeners in JavaScript?

68. What is the difference between addEventListener and onclick?

69. How do you remove an event listener?

70. What are synthetic events in JavaScript?

JavaScript Async Programming Questions

71. What is AJAX in JavaScript?

72. How do you make an HTTP request using fetch()?

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

74. What is CORS in JavaScript?

75. How do WebSockets work in JavaScript?

76. What is a Service Worker?

77. What are Web Workers?

78. How does JavaScript handle concurrency?

79. What are Promise.all(), Promise.any(), and Promise.race()?

80. What is the difference between async and defer attributes in script tags?

JavaScript Security Questions

81. What is Cross-Site Scripting (XSS), and how do you prevent it?

82. What is Cross-Site Request Forgery (CSRF), and how do you prevent it?

83. What are Content Security Policies (CSP)?

84. How do you prevent SQL injection in JavaScript?

85. What are HTTP-only cookies?

86. What is CORS, and how does it work?

87. How do you handle security issues in JWT authentication?

88. What is sandbox in iframes?

89. What are security best practices for handling user input?

90. How do you prevent clickjacking attacks?

Miscellaneous Advanced JavaScript Questions

91. What is the difference between document.ready and window.onload?

92. What is the difference between console.log(), console.warn(), and console.error()?

93. What are template engines in JavaScript?

94. How do you lazy load images in JavaScript?

95. What is the difference between npm and yarn?

96. What is the difference between require and import?

97. What is the Intl API in JavaScript?

98. How do you handle large datasets efficiently in JavaScript?

99. What is functional programming, and how does JavaScript support it?

100. What is the difference between imperative and declarative programming in JavaScript?