Top 90+ JavaScript Interview Questions and Answers(Updated 2024)

JavaScript: Important Interview Questions

Top 90+ javascript questions handpicked by us to succeed in any interview. You should go through each of this question before appearing for frontend developer interviews.

1. What are falsy values in JavaScript?
2. Data Types in Javascript
3. ForEach, Map, Filter and Reduce in Javascript
4. What is Prototypal inheritance in javascript?
5. What is Generator Function in Javascript
6. Caching related questions (Headers, Expiry, Types etc)
7. PWA related concepts ( Service Workers, Manifest etc)
8. Difference between Server Side Rendering vs Client side rendering
9. Throttle & Debounce in Javascript
10. What is Iterators in Javascript?
11. Pollyfills for in built methods(Array methods, Call, bind, apply, promise etc)
12. Difference between Split, Replace, Splice, Slice?
13. Query Selector in Javascript
14. String related methods in javascript (substring, trim etc)
15. Datatypes and Typeof related output questions in javascript
16. HTML5 new features(Semantic elements)
17. What is Web worker in Javascript and how it works?
18. What is This in Javascript?
19. What is Closure in javascript?
20. Memoization in javascript
21. Hoisting in javascript?
22. What is Design Patterns and its uses in Javascript( Modular, Factory, Observer, Pub Sub, Singleton etc)
23. Currying in javascript and related questions?
24. What is Call, Apply, Bind in Javascript?
25. What is Prototype Chain in Javascript?
26. Declaring and extending classes using functions in Javascript(Difference between ES6 and ES5)
27. What is Promises in javascript?
28. What is arrow functions in Javascript?
29. What is ES6 and it's features;
30. Anonymous function in Javascript?
31. How to flatten a nested array in Javascript?
32. How to declare private variable in Javascript?
33. Destructing of objects in Javascript.
34. How Async and defer works in script tag?
35. Difference between rest operator and spread operator?
36. How Fetch() works in Javascript?
37. Single page application architecture
38. SEO related concepts
39. What is XHR requests and how it's works?
40. How Javascript works under the hood?
41. Message Queue in JS
42. Job Queue in JS
43. Call Stack in JS
44. event loop and JS Engine
45. Decimal to Hexadecimal conversions
46. Why do we use “use strict” in javascript?
47. What is pure function in Javascript?
48. let, var and const in javascript
49. What is IIFE?
50. Data-ng attributes
51. Dom tree implementation and traversal?
52. What is reactive programming?
53. React based javascript interview questions
54. Virtual DOM Implementation of React
55. Hooks – Usestate, useeffect, useref, useCallback, useMemo
56. Pure Components in React
57. Higher Order Components in React
58. Styled Components in React
59. Context API in React
60. Redux based javascript interview questions
61. How redux works and Design Pattern behind redux?
62. What is Shadow DOM?
63. Frameworks specific questions based on your resume and previous experience.
64. What is Event propagation, capturing, bubbling ?
65. Event listner in javascript and how it work?
66. Web Storage in javascript
67. How to access nested objects and listing all key value pairs in javascript?
68. Load balancers working
69. How to scale applications?
70. How does CDN works?
71. Implementation of linked lists in javascript?
72. All ES6 features
73. JSON parse, stringify etc
74. How does webpack works(dependency graph, chunk formation etc)?
75. How does babel works?
76. Node JS based basic javascript interview questions
77. Deprecated react lifecycles and their drawbacks?
78. Optimization of the problems that you are going to solve?
79. Frameworks vs VanillaJS, advantages and disadvantages?
80. What is Promises in javascript?
81. How to create Deep vs Shallow Copy in Javascript?
82. Binary Search related questions in javascript.
83. How to delete Object Keys in javascript?
84. HasOwnProperty in Javascript Objects
85. Two way binding implementation in javascript.
86. Binding and it's types(Implicit/Hard/Explicit/New)
87. Callback vs Promise in javascript
88. What is callback hell?
89. Async/Await over Promise
90. Eval Function in JS
91. Javascript Object methods (isExtensible, freeze, sealed)
92. What is the use of setTimeout, setInterval and related output question?
93. Output based tricky questions based on javascript concepts
94. What is the purpose of void 0?
95. How to create table using object oriented javascript
96. Frontend Interview Guide