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JavaScript Coding Questions
As a Front-End developer, JavaScript is the core skill of everything
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Difficulty
Solved status
Company
Sort: most accepted
1. implement curry()
JavaScript
easy
21232 accepted
3. implement Array.prototype.flat()
JavaScript
easy
17254 accepted
4. implement basic throttle()
JavaScript
Lodash
medium
12830 accepted
6. implement basic debounce()
JavaScript
Lodash
easy
11752 accepted
19. find corresponding node in two identical DOM tree
JavaScript
easy
8513 accepted
16. create an Event Emitter
JavaScript
medium
8226 accepted
11. what is Composition? create a pipe()
JavaScript
easy
6586 accepted
2. implement curry() with placeholder support
JavaScript
medium
6447 accepted
17. Create a simple store for DOM element
JavaScript
easy
6343 accepted
14. Implement a general memoization function - `memo()`
JavaScript
medium
6150 accepted
32. implement `Promise.all()`
JavaScript
medium
5860 accepted
28. implement clearAllTimeout()
JavaScript
easy
5510 accepted
18. Improve a function
JavaScript
easy
5485 accepted
8. can you shuffle() an array?
JavaScript
medium
5053 accepted
176. undefined to null
JavaScript
easy
4884 accepted
9. decode message
JavaScript
medium
4600 accepted
7. implement debounce() with leading & trailing option
JavaScript
Lodash
medium
4570 accepted
10. first bad version
JavaScript
Algorithm
medium
4566 accepted
58. get DOM tree height
JavaScript
Algorithm
DOM
medium
4564 accepted
23. create a sum()
JavaScript
easy
4464 accepted
5. implement throttle() with leading & trailing option
JavaScript
Lodash
medium
4410 accepted
167. Intersection of unsorted arrays
JavaScript
Algorithm
easy
4375 accepted
151. implement Array.prototype.map()
JavaScript
medium
4176 accepted
162. find the single integer
JavaScript
Algorithm
easy
3937 accepted
15. implement a simple DOM wrapper to support method chaining like jQuery
JavaScript
easy
3848 accepted
165. remove characters
Algorithm
medium
3740 accepted
25. Reorder array with new indexes
JavaScript
Algorithm
easy
3701 accepted
155. create a count function
JavaScript
easy
3482 accepted
159. implement promisify()
JavaScript
easy
3227 accepted
33. implement `Promise.allSettled()`
JavaScript
medium
3180 accepted
35. implement `Promise.race()`
JavaScript
easy
3144 accepted
29. implement async helper - `sequence()`
JavaScript
medium
3138 accepted
148. create a counter object
JavaScript
easy
3093 accepted
113. Virtual DOM I
JavaScript
Algorithm
DOM
medium
3092 accepted
34. implement `Promise.any()`
JavaScript
medium
3060 accepted
161. toBe() or not.toBe()
JavaScript
medium
2784 accepted
154. Two-way binding
JavaScript
DOM
easy
2729 accepted
92. throttle Promises
JavaScript
medium
2694 accepted
64. auto-retry Promise on rejection
JavaScript
medium
2628 accepted
13. Implement a Queue by using Stack
JavaScript
Algorithm
medium
2553 accepted
68. get DOM tags
JavaScript
Algorithm
DOM
medium
2526 accepted
104. Traverse DOM level by level
JavaScript
Algorithm
DOM
medium
2524 accepted
57. create an Observable
JavaScript
medium
2471 accepted
91. invert a binary tree
JavaScript
Algorithm
easy
2436 accepted
146. implement Array.prototype.reduce()
JavaScript
medium
2338 accepted
39. implement range()
JavaScript
easy
2338 accepted
89. Next Right Sibling
JavaScript
DOM
easy
2276 accepted
157. semver compare
JavaScript
easy
2185 accepted
67. create your own Promise
JavaScript
medium
2114 accepted
26. implement Object.assign()
JavaScript
medium
2111 accepted
110. serialize and deserialize binary tree
JavaScript
Algorithm
medium
2071 accepted
30. implement async helper - `parallel()`
JavaScript
medium
2014 accepted
12. implement Immutability helper
JavaScript
medium
2014 accepted
168. move zeros
JavaScript
Algorithm
medium
1997 accepted
20. Detect data type in JavaScript
JavaScript
medium
1994 accepted
60. create your own `new` operator
JavaScript
easy
1952 accepted
37. implement Binary Search (unique)
JavaScript
easy
1924 accepted
47. reverse a linked list
JavaScript
Algorithm
easy
1823 accepted
145. most frequently occurring character
JavaScript
easy
1813 accepted
63. create `_.cloneDeep()`
JavaScript
Algorithm
Lodash
medium
1810 accepted
46. implement `_.once()`
JavaScript
Lodash
easy
1793 accepted
21. implement JSON.stringify()
JavaScript
medium
1768 accepted
31. implement async helper - `race()`
JavaScript
easy
1762 accepted
56. call APIs with pagination
JavaScript
medium
1699 accepted
163. integer to roman numerals
JavaScript
Algorithm
easy
1645 accepted
133. roman numerals to integer
JavaScript
easy
1604 accepted
123. implement Promise.prototype.finally()
JavaScript
medium
1589 accepted
61. create your own `Function.prototype.call`
JavaScript
medium
1580 accepted
118. Virtual DOM II - createElement
JavaScript
easy
1570 accepted
40. implement Bubble Sort
JavaScript
Algorithm
easy
1570 accepted
103. implement Math.sqrt()
JavaScript
Algorithm
medium
1542 accepted
158. Previous Left Sibling
JavaScript
DOM
medium
1489 accepted
85. implement `_.get()`
JavaScript
Lodash
medium
1462 accepted
125. implement classNames()
JavaScript
medium
1444 accepted
121. A number sequence
JavaScript
easy
1425 accepted
105. find the first duplicate character in a string
JavaScript
string
easy
1418 accepted
107. Find the largest difference
JavaScript
Algorithm
easy
1408 accepted
81. merge sorted arrays
JavaScript
Algorithm
easy
1375 accepted
138. Intersection of two sorted arrays
JavaScript
Algorithm
easy
1357 accepted
94. implement your own `Object.create`
JavaScript
easy
1351 accepted
53. write your own `extends` in es5
JavaScript
medium
1347 accepted
69. implement deep equal `_.isEqual()`
JavaScript
Lodash
medium
1339 accepted
38. implement `jest.spyOn()`
JavaScript
easy
1314 accepted
120. create `isPrime()`
JavaScript
Algorithm
easy
1288 accepted
131. implement _.chunk()
JavaScript
Lodash
medium
1284 accepted
130. create LazyMan()
JavaScript
medium
1278 accepted
106. Find two numbers that sum up to 0
JavaScript
Algorithm
easy
1278 accepted
102. validate string of parentheses
JavaScript
Algorithm
string
easy
1271 accepted
122. implement memoizeOne()
JavaScript
medium
1269 accepted
48. search first index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1205 accepted
86. Generate Fibonacci Number
JavaScript
Algorithm
medium
1187 accepted
97. compress a string
JavaScript
string
easy
1184 accepted
140. Virtual DOM III - Functional Component
JavaScript
easy
1177 accepted
87. longest substring with unique characters
JavaScript
Algorithm
easy
1166 accepted
83. create an interval
JavaScript
medium
1162 accepted
66. remove duplicates from an array
JavaScript
Algorithm
medium
1149 accepted
173. uncompress string
JavaScript
string
algorithm
medium
1140 accepted
54. flatten Thunk
JavaScript
easy
1137 accepted
36. create a fake timer(setTimeout)
JavaScript
medium
1084 accepted
152. Find Top k Elements
JavaScript
Algorithm
medium
1081 accepted
156. implement `_.set()`
JavaScript
Lodash
medium
1077 accepted
109. implement `Math.pow()`
JavaScript
Algorithm
easy
1064 accepted
116. implement Object.is()
JavaScript
easy
1061 accepted
90. write your own `instanceof`
JavaScript
medium
1022 accepted
24. create a Priority Queue in JavaScript
JavaScript
Algorithm
medium
1008 accepted
49. search last index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1006 accepted
65. add comma to number
JavaScript
medium
1002 accepted
55. highlight keywords in HTML string
JavaScript
Algorithm
medium
1000 accepted
22. implement JSON.parse()
JavaScript
medium
987 accepted
59. create a browser history
JavaScript
medium
963 accepted
93. Generate Fibonacci Number with recursion
JavaScript
easy
956 accepted
147. Pick up stones
JavaScript
easy
942 accepted
100. detect circle in linked list
JavaScript
Algorithm
easy
938 accepted
27. implement completeAssign()
JavaScript
medium
933 accepted
42. implement Insertion Sort
JavaScript
Algorithm
easy
932 accepted
135. localStorage with expiration
JavaScript
medium
914 accepted
43. implement Quick Sort
JavaScript
Algorithm
medium
896 accepted
101. merge identical API calls
JavaScript
medium
888 accepted
139. implement _.partial()
JavaScript
Lodash
medium
878 accepted
52. create a middleware system
JavaScript
medium
853 accepted
79. convert snake_case to camelCase
JavaScript
medium
829 accepted
95. implement String.prototype.trim()
JavaScript
medium
820 accepted
170. Generate CSS Selector for target element
JavaScript
medium
808 accepted
41. implement Merge Sort
JavaScript
Algorithm
medium
805 accepted
44. implement Selection Sort
JavaScript
Algorithm
easy
797 accepted
50. search element right before target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
794 accepted
82. find available meeting slots
JavaScript
Algorithm
medium
776 accepted
88. support negative Array index in JavaScript
JavaScript
medium
735 accepted
166. validate number string
JavaScript
Algorithm
string
medium
728 accepted
51. search element right after target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
725 accepted
117. event delegation
JavaScript
medium
723 accepted
149. interpolation
JavaScript
medium
714 accepted
136. find median of two sorted array
JavaScript
Algorithm
medium
693 accepted
96. count "1" in binary form
JavaScript
easy
693 accepted
45. find the K-th largest element in an unsorted array
JavaScript
Algorithm
medium
669 accepted
62. implement BigInt addition
JavaScript
Algorithm
easy
653 accepted
111. Count palindromic substrings
JavaScript
Algorithm
string
medium
632 accepted
132. the angle between hour hand and minute hand of a clock
JavaScript
medium
627 accepted
108. Implement a Stack by using Queue
JavaScript
Algorithm
medium
601 accepted
119. create a tokenizer
JavaScript
medium
551 accepted
153. uglify CSS class names
JavaScript
medium
541 accepted
112. remove duplicate characters in a string
JavaScript
Algorithm
string
medium
532 accepted
142. lit-html 1 - tagged templates
JavaScript
lit-html
easy
522 accepted
172. implement `Math.clz32()`
JavaScript
medium
507 accepted
70. implement Observable.from()
JavaScript
medium
506 accepted
80. implement your own URLSearchParams
JavaScript
hard?
504 accepted
134. create your own Cookie
JavaScript
medium
470 accepted
84. create a fake timer (setInterval)
JavaScript
medium
467 accepted
137. binary tree vertical traversal
JavaScript
Algorithm
hard?
463 accepted
71. implement Observable Subject
JavaScript
medium
442 accepted
99. extract all anchor element from HTML string
JavaScript
medium
431 accepted
171. create callback on message channel
JavaScript
medium
400 accepted
164. implement Immer produce()
JavaScript
medium
395 accepted
72. implement Observable interval()
JavaScript
easy
395 accepted
75. implement BigInt subtraction
JavaScript
Algorithm
medium
369 accepted
74. implement Observable Transformation Operators
JavaScript
easy
368 accepted
73. implement Observable fromEvent()
JavaScript
easy
359 accepted
98. validate an IP address
JavaScript
medium
336 accepted
169. LRU - Chrome storage automatic eviction
JavaScript
Algorithm
medium
308 accepted
78. convert HEX color to RGBA
JavaScript
medium
290 accepted
143. Virtual DOM IV - JSX 1
JavaScript
medium
265 accepted
141. implement btoa()
JavaScript
easy
228 accepted
124. calculate arithmetic expression
JavaScript
Algorithm
medium
195 accepted
76. implement BigInt addition with sign
JavaScript
medium
176 accepted
160. implement atob()
JavaScript
medium
167 accepted
144. serialize and deserialize data types not supported in JSON
JavaScript
medium
145 accepted
150. Virtual DOM V - JSX 2
JavaScript
medium
129 accepted
114. implement BigInt multiplication
JavaScript
medium
129 accepted
77. implement BigInt subtraction with sign
JavaScript
medium
103 accepted
115. implement BigInt division
JavaScript
medium
61 accepted
126. BigDecimal addition
JavaScript
Algorithm
medium
54 accepted
174. CSS Grid Layout auto-placement algorithm - sparse
JavaScript
CSS
hard?
47 accepted
129. BigDecimal Division
JavaScript
Algorithm
medium
34 accepted
128. BigDecimal multiplication
JavaScript
Algorithm
medium
33 accepted
127. BigDecimal subtraction
JavaScript
Algorithm
few challengers
27 accepted
175. CSS Grid Layout auto-placement algorithm - dense
JavaScript
CSS
medium
13 accepted