JavaScript Interview Questions

Prepare for JavaScript interviews with our comprehensive guide. Master key concepts, tackle challenging questions, and ace your next JavaScript interview.

1. What is JavaScript, and what is it used for?
2. What are the different data types in JavaScript?
3. What is the difference between 'null' and 'undefined' in JavaScript?
4. What is a variable in JavaScript, and how is it declared?
5. What is scope in JavaScript?
6. What is the difference between global scope and local scope in JavaScript?
7. What is hoisting in JavaScript?
8. What is the 'use strict' directive in JavaScript, and why is it used?
9. What is NaN in JavaScript, and how is it handled?
10. What is the difference between '==' and '===' operators in JavaScript?
11. What are the different operators in JavaScript?
12. What is the ternary operator in JavaScript, and how is it used?
13. What are the different loops in JavaScript?
14. What is the 'this' keyword in JavaScript, and how is it used?
15. What is the difference between 'call()' and 'apply()' methods in JavaScript?
16. What is a function in JavaScript, and how is it declared?
17. What is a callback function in JavaScript, and how is it used?
18. What is a higher-order function in JavaScript, and how is it used?
19. What is an anonymous function in JavaScript, and how is it used?
20. What is a closure in JavaScript, and how is it used?
21. What is an arrow function in JavaScript, and how is it used?
22. What is a generator function in JavaScript, and how is it used?
23. What is a Promise in JavaScript, and how is it used?
24. What is the difference between 'async' and 'await' in JavaScript?
25. What are the different types of error handling in JavaScript?
26. What is a try-catch block in JavaScript, and how is it used?
27. What is a throw statement in JavaScript, and how is it used?
28. What is the 'finally' block in JavaScript, and how is it used?
29. What is an event in JavaScript, and how is it handled?
30. What is the difference between 'addEventListener' and 'attachEvent' methods in JavaScript?
31. What is a callback function in event handling in JavaScript, and how is it used?
32. What is the difference between 'preventDefault' and 'stopPropagation' methods in JavaScript?
33. What is JSON, and how is it used in JavaScript?
34. What is the difference between 'JSON.parse()' and 'JSON.stringify()' methods in JavaScript?
35. What is AJAX, and how is it used in JavaScript?
36. What is the XMLHttpRequest object in JavaScript, and how is it used?
37. What is the fetch API in JavaScript, and how is it used?
38. What is a module in JavaScript, and how is it used?
39. What is the difference between 'export' and 'export default' statements in JavaScript?
40. What is the 'import' statement in JavaScript, and how is it used?
41. What is the difference between 'var', 'let', and 'const' keywords in JavaScript?
42. What is the difference between 'undefined' and 'null' in JavaScript?
43. What are the different types of loops in JavaScript?
44. What is the difference between 'for' and 'forEach' loops in JavaScript?
45. What is the difference between 'map()', 'filter()', 'reduce()', and 'find()' methods in JavaScript?
46. What is the difference between 'slice()' and 'splice()' methods in JavaScript?
47. What is the difference between 'indexOf()' and 'includes()' methods in JavaScript?
48. What is the difference between 'push()' and 'pop()' methods in JavaScript?
49. What is the difference between 'shift()' and 'unshift()' methods in JavaScript?
50. What is the difference between 'concat()' and 'join()' methods in JavaScript?
51. What is the difference between 'sort()' and 'reverse()' methods in JavaScript?
52. What is the difference between 'charAt()' and 'charCodeAt()' methods in JavaScript?
53. What is the difference between 'toUpperCase()' and 'toLowerCase()' methods in JavaScript?
54. What is the difference between 'trim()' and 'trimStart()/trimEnd()' methods in JavaScript?
55. What is the difference between 'split()' and 'match()' methods in JavaScript?
56. What is the difference between 'Math.random()' and 'Math.floor()' methods in JavaScript?
57. What is the difference between 'setInterval()' and 'setTimeout()' methods in JavaScript?
58. What is the difference between 'window' and 'document' objects in JavaScript?
59. What is the difference between 'innerHTML' and 'textContent' properties in JavaScript?
60. What is the difference between 'getAttribute()' and 'setAttribute()' methods in JavaScript?
61. What is the difference between 'classList' and 'className' properties in JavaScript?
62. What is the difference between 'createElement()' and 'createTextNode()' methods in JavaScript?
63. What is the difference between 'appendChild()' and 'insertBefore()' methods in JavaScript?
64. What is the difference between 'cloneNode()' and 'deepClone()' methods in JavaScript?
65. What is the difference between 'getComputedStyle()' and 'currentStyle' properties in JavaScript?
66. What is the difference between 'addEventListener()' and 'removeEventListener()' methods in JavaScript?
67. What is the difference between 'target' and 'currentTarget' properties in JavaScript?
68. What is the difference between 'stopPropagation()' and 'stopImmediatePropagation()' methods in JavaScript?
69. What is the difference between 'defaultPrevented' and 'returnValue' properties in JavaScript?
70. What is the difference between 'querySelector()' and 'getElementById()' methods in JavaScript?
71. What is the difference between 'querySelectorAll()' and 'getElementsByClassName()' methods in JavaScript?
72. What is the difference between 'matches()' and 'closest()' methods in JavaScript?
73. What is the difference between 'localStorage' and 'sessionStorage' in JavaScript?
74. What is the difference between 'get()' and 'post()' methods in AJAX?
75. What is the difference between 'onreadystatechange' and 'readystatechange()' methods in AJAX?
76. What is the difference between 'open()' and 'send()' methods in AJAX?
77. What is the difference between 'readystatechange' and 'load' events in AJAX?
78. What is the difference between 'GET' and 'POST' requests in AJAX?
79. What is the difference between 'serialize()' and 'serializeArray()' methods in AJAX?
80. What is the difference between 'async' and 'defer' attributes in script tags?
81. What is the difference between 'DOMContentLoaded' and 'load' events in JavaScript?
82. What is the difference between 'setTimeout()' and 'setImmediate()' methods in JavaScript?
83. What is the difference between 'Symbol.iterator' and 'for...of' loop in JavaScript?
84. What is the difference between 'Promise.resolve()' and 'Promise.reject()' methods in JavaScript?
85. What is the difference between 'Promise.all()' and 'Promise.race()' methods in JavaScript?
86. What is the difference between 'async/await' and 'Promise' methods in JavaScript?
87. What is the difference between 'super()' and 'super' keywords in JavaScript?
88. What is the difference between 'Object.keys()' and 'Object.getOwnPropertyNames()' methods in JavaScript?
89. What is the difference between 'Object.create()' and 'new' keyword in JavaScript?
90. What is the difference between 'Object.freeze()' and 'Object.seal()' methods in JavaScript?
91. What is the difference between 'Function.call()' and 'Function.apply()' methods in JavaScript?
92. What is the difference between 'bind()' and 'call()' methods in JavaScript?
93. What is the difference between 'prototype' and 'proto' properties in JavaScript?
94. What is the difference between 'Object.create()' and 'proto' property in JavaScript?
95. What is the difference between 'Promise' and 'Observable' in JavaScript?
96. What is the difference between 'Generator' and 'Async' functions in JavaScript?
97. What is the difference between 'Object.assign()' and 'spread operator(...)' in JavaScript?
98. What is the difference between 'ES6' and 'ES5' in JavaScript?
99. What is 'this' keyword in JavaScript?
100. How to use 'this' keyword in JavaScript?
101. What is the difference between 'call()', 'apply()', and 'bind()' methods in JavaScript?
102. How to use 'call()', 'apply()', and 'bind()' methods in JavaScript?
103. What is 'window' object in JavaScript?
104. What is 'document' object in JavaScript?
105. What is 'event' object in JavaScript?
106. What is 'target' property in 'event' object in JavaScript?
107. What is 'currentTarget' property in 'event' object in JavaScript?
108. What is 'preventDefault()' method in 'event' object in JavaScript?
109. What is 'stopPropagation()' method in 'event' object in JavaScript?
110. What is 'capturing' and 'bubbling' in 'event' object in JavaScript?
111. What is 'addEventListener()' method in JavaScript?
112. How to use 'addEventListener()' method in JavaScript?
113. What is 'removeEventListener()' method in JavaScript?
114. How to use 'removeEventListener()' method in JavaScript?
115. What is 'setTimeout()' method in JavaScript?
116. How to use 'setTimeout()' method in JavaScript?
117. What is 'setInterval()' method in JavaScript?
118. How to use 'setInterval()' method in JavaScript?
119. What is 'clearTimeout()' method in JavaScript?
120. How to use 'clearTimeout()' method in JavaScript?
121. What is 'clearInterval()' method in JavaScript?
122. How to use 'clearInterval()' method in JavaScript?
123. What is 'JSON' in JavaScript?
124. How to parse JSON string in JavaScript?
125. How to stringify JSON object in JavaScript?
126. What is 'XMLHttpRequest' in JavaScript?
127. How to use 'XMLHttpRequest' in JavaScript?
128. What is 'fetch()' in JavaScript?
129. How to use 'fetch()' in JavaScript?
130. What is 'Promise' in JavaScript?
131. How to use 'Promise' in JavaScript?
132. What is 'async/await' in JavaScript?
133. How to use 'async/await' in JavaScript?
134. What is 'callback' function in JavaScript?
135. How to use 'callback' function in JavaScript?
136. What is 'closure' in JavaScript?
137. How to use 'closure' in JavaScript?
138. What is 'prototype' in JavaScript?
139. How to use 'prototype' in JavaScript?
140. What is 'inheritance' in JavaScript?
141. How to use 'inheritance' in JavaScript?
142. What is 'ES6 class' in JavaScript?
143. What is 'arrow function' in JavaScript?
144. How to use 'arrow function' in JavaScript?
145. What is 'template literal' in JavaScript?
146. How to use 'template literal' in JavaScript?
147. What is 'destructuring' in JavaScript?
148. How to use 'destructuring' in JavaScript?