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JavaScript Coding Questions
As a Front-End developer, JavaScript is the core skill of everything
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Sort: most accepted
tag: JavaScript
1. implement curry()
JavaScript
easy
21065 accepted
3. implement Array.prototype.flat()
JavaScript
easy
17131 accepted
4. implement basic throttle()
JavaScript
Lodash
medium
12752 accepted
6. implement basic debounce()
JavaScript
Lodash
easy
11635 accepted
19. find corresponding node in two identical DOM tree
JavaScript
easy
8476 accepted
16. create an Event Emitter
JavaScript
medium
8177 accepted
11. what is Composition? create a pipe()
JavaScript
easy
6544 accepted
2. implement curry() with placeholder support
JavaScript
medium
6406 accepted
17. Create a simple store for DOM element
JavaScript
easy
6319 accepted
14. Implement a general memoization function - `memo()`
JavaScript
medium
6080 accepted
32. implement `Promise.all()`
JavaScript
medium
5795 accepted
28. implement clearAllTimeout()
JavaScript
easy
5482 accepted
18. Improve a function
JavaScript
easy
5458 accepted
8. can you shuffle() an array?
JavaScript
medium
5033 accepted
176. undefined to null
JavaScript
easy
4802 accepted
9. decode message
JavaScript
medium
4578 accepted
58. get DOM tree height
JavaScript
Algorithm
DOM
medium
4550 accepted
10. first bad version
JavaScript
Algorithm
medium
4540 accepted
7. implement debounce() with leading & trailing option
JavaScript
Lodash
medium
4538 accepted
23. create a sum()
JavaScript
easy
4433 accepted
5. implement throttle() with leading & trailing option
JavaScript
Lodash
medium
4382 accepted
167. Intersection of unsorted arrays
JavaScript
Algorithm
easy
4339 accepted
151. implement Array.prototype.map()
JavaScript
medium
4148 accepted
162. find the single integer
JavaScript
Algorithm
easy
3901 accepted
15. implement a simple DOM wrapper to support method chaining like jQuery
JavaScript
easy
3816 accepted
25. Reorder array with new indexes
JavaScript
Algorithm
easy
3679 accepted
155. create a count function
JavaScript
easy
3461 accepted
159. implement promisify()
JavaScript
easy
3196 accepted
33. implement `Promise.allSettled()`
JavaScript
medium
3154 accepted
29. implement async helper - `sequence()`
JavaScript
medium
3129 accepted
35. implement `Promise.race()`
JavaScript
easy
3116 accepted
113. Virtual DOM I
JavaScript
Algorithm
DOM
medium
3086 accepted
148. create a counter object
JavaScript
easy
3077 accepted
34. implement `Promise.any()`
JavaScript
medium
3038 accepted
161. toBe() or not.toBe()
JavaScript
medium
2781 accepted
154. Two-way binding
JavaScript
DOM
easy
2724 accepted
92. throttle Promises
JavaScript
medium
2681 accepted
64. auto-retry Promise on rejection
JavaScript
medium
2604 accepted
13. Implement a Queue by using Stack
JavaScript
Algorithm
medium
2539 accepted
68. get DOM tags
JavaScript
Algorithm
DOM
medium
2517 accepted
104. Traverse DOM level by level
JavaScript
Algorithm
DOM
medium
2514 accepted
57. create an Observable
JavaScript
medium
2459 accepted
91. invert a binary tree
JavaScript
Algorithm
easy
2421 accepted
39. implement range()
JavaScript
easy
2329 accepted
146. implement Array.prototype.reduce()
JavaScript
medium
2320 accepted
89. Next Right Sibling
JavaScript
DOM
easy
2266 accepted
157. semver compare
JavaScript
easy
2174 accepted
26. implement Object.assign()
JavaScript
medium
2103 accepted
67. create your own Promise
JavaScript
medium
2094 accepted
110. serialize and deserialize binary tree
JavaScript
Algorithm
medium
2067 accepted
30. implement async helper - `parallel()`
JavaScript
medium
2003 accepted
12. implement Immutability helper
JavaScript
medium
2001 accepted
20. Detect data type in JavaScript
JavaScript
medium
1982 accepted
168. move zeros
JavaScript
Algorithm
medium
1974 accepted
60. create your own `new` operator
JavaScript
easy
1939 accepted
37. implement Binary Search (unique)
JavaScript
easy
1910 accepted
145. most frequently occurring character
JavaScript
easy
1807 accepted
47. reverse a linked list
JavaScript
Algorithm
easy
1807 accepted
63. create `_.cloneDeep()`
JavaScript
Algorithm
Lodash
medium
1793 accepted
46. implement `_.once()`
JavaScript
Lodash
easy
1777 accepted
21. implement JSON.stringify()
JavaScript
medium
1762 accepted
31. implement async helper - `race()`
JavaScript
easy
1746 accepted
56. call APIs with pagination
JavaScript
medium
1693 accepted
163. integer to roman numerals
JavaScript
Algorithm
easy
1633 accepted
133. roman numerals to integer
JavaScript
easy
1591 accepted
123. implement Promise.prototype.finally()
JavaScript
medium
1581 accepted
118. Virtual DOM II - createElement
JavaScript
easy
1565 accepted
40. implement Bubble Sort
JavaScript
Algorithm
easy
1563 accepted
61. create your own `Function.prototype.call`
JavaScript
medium
1553 accepted
103. implement Math.sqrt()
JavaScript
Algorithm
medium
1535 accepted
158. Previous Left Sibling
JavaScript
DOM
medium
1487 accepted
85. implement `_.get()`
JavaScript
Lodash
medium
1446 accepted
125. implement classNames()
JavaScript
medium
1436 accepted
121. A number sequence
JavaScript
easy
1415 accepted
105. find the first duplicate character in a string
JavaScript
string
easy
1405 accepted
107. Find the largest difference
JavaScript
Algorithm
easy
1401 accepted
81. merge sorted arrays
JavaScript
Algorithm
easy
1355 accepted
138. Intersection of two sorted arrays
JavaScript
Algorithm
easy
1347 accepted
53. write your own `extends` in es5
JavaScript
medium
1345 accepted
94. implement your own `Object.create`
JavaScript
easy
1341 accepted
69. implement deep equal `_.isEqual()`
JavaScript
Lodash
medium
1319 accepted
38. implement `jest.spyOn()`
JavaScript
easy
1306 accepted
120. create `isPrime()`
JavaScript
Algorithm
easy
1274 accepted
131. implement _.chunk()
JavaScript
Lodash
medium
1273 accepted
130. create LazyMan()
JavaScript
medium
1273 accepted
106. Find two numbers that sum up to 0
JavaScript
Algorithm
easy
1269 accepted
122. implement memoizeOne()
JavaScript
medium
1261 accepted
102. validate string of parentheses
JavaScript
Algorithm
string
easy
1254 accepted
48. search first index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1201 accepted
86. Generate Fibonacci Number
JavaScript
Algorithm
medium
1179 accepted
97. compress a string
JavaScript
string
easy
1175 accepted
140. Virtual DOM III - Functional Component
JavaScript
easy
1173 accepted
83. create an interval
JavaScript
medium
1152 accepted
87. longest substring with unique characters
JavaScript
Algorithm
easy
1149 accepted
66. remove duplicates from an array
JavaScript
Algorithm
medium
1137 accepted
54. flatten Thunk
JavaScript
easy
1135 accepted
173. uncompress string
JavaScript
string
algorithm
medium
1122 accepted
36. create a fake timer(setTimeout)
JavaScript
medium
1078 accepted
152. Find Top k Elements
JavaScript
Algorithm
medium
1074 accepted
156. implement `_.set()`
JavaScript
Lodash
medium
1069 accepted
116. implement Object.is()
JavaScript
easy
1057 accepted
109. implement `Math.pow()`
JavaScript
Algorithm
easy
1055 accepted
90. write your own `instanceof`
JavaScript
medium
1006 accepted
24. create a Priority Queue in JavaScript
JavaScript
Algorithm
medium
1004 accepted
65. add comma to number
JavaScript
medium
999 accepted
55. highlight keywords in HTML string
JavaScript
Algorithm
medium
999 accepted
49. search last index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
999 accepted
22. implement JSON.parse()
JavaScript
medium
987 accepted
59. create a browser history
JavaScript
medium
957 accepted
93. Generate Fibonacci Number with recursion
JavaScript
easy
949 accepted
147. Pick up stones
JavaScript
easy
935 accepted
27. implement completeAssign()
JavaScript
medium
932 accepted
100. detect circle in linked list
JavaScript
Algorithm
easy
927 accepted
42. implement Insertion Sort
JavaScript
Algorithm
easy
925 accepted
135. localStorage with expiration
JavaScript
medium
910 accepted
43. implement Quick Sort
JavaScript
Algorithm
medium
893 accepted
101. merge identical API calls
JavaScript
medium
878 accepted
139. implement _.partial()
JavaScript
Lodash
medium
870 accepted
52. create a middleware system
JavaScript
medium
851 accepted
79. convert snake_case to camelCase
JavaScript
medium
822 accepted
95. implement String.prototype.trim()
JavaScript
medium
813 accepted
170. Generate CSS Selector for target element
JavaScript
medium
804 accepted
41. implement Merge Sort
JavaScript
Algorithm
medium
801 accepted
44. implement Selection Sort
JavaScript
Algorithm
easy
791 accepted
50. search element right before target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
786 accepted
82. find available meeting slots
JavaScript
Algorithm
medium
771 accepted
88. support negative Array index in JavaScript
JavaScript
medium
727 accepted
166. validate number string
JavaScript
Algorithm
string
medium
722 accepted
51. search element right after target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
721 accepted
117. event delegation
JavaScript
medium
715 accepted
149. interpolation
JavaScript
medium
711 accepted
96. count "1" in binary form
JavaScript
easy
689 accepted
136. find median of two sorted array
JavaScript
Algorithm
medium
684 accepted
45. find the K-th largest element in an unsorted array
JavaScript
Algorithm
medium
668 accepted
62. implement BigInt addition
JavaScript
Algorithm
easy
648 accepted
111. Count palindromic substrings
JavaScript
Algorithm
string
medium
630 accepted
132. the angle between hour hand and minute hand of a clock
JavaScript
medium
626 accepted
108. Implement a Stack by using Queue
JavaScript
Algorithm
medium
597 accepted
119. create a tokenizer
JavaScript
medium
550 accepted
153. uglify CSS class names
JavaScript
medium
539 accepted
112. remove duplicate characters in a string
JavaScript
Algorithm
string
medium
528 accepted
142. lit-html 1 - tagged templates
JavaScript
lit-html
easy
519 accepted
172. implement `Math.clz32()`
JavaScript
medium
506 accepted
80. implement your own URLSearchParams
JavaScript
hard?
502 accepted
70. implement Observable.from()
JavaScript
medium
502 accepted
134. create your own Cookie
JavaScript
medium
469 accepted
84. create a fake timer (setInterval)
JavaScript
medium
466 accepted
137. binary tree vertical traversal
JavaScript
Algorithm
hard?
463 accepted
71. implement Observable Subject
JavaScript
medium
437 accepted
99. extract all anchor element from HTML string
JavaScript
medium
428 accepted
171. create callback on message channel
JavaScript
medium
398 accepted
164. implement Immer produce()
JavaScript
medium
395 accepted
72. implement Observable interval()
JavaScript
easy
394 accepted
75. implement BigInt subtraction
JavaScript
Algorithm
medium
368 accepted
74. implement Observable Transformation Operators
JavaScript
easy
365 accepted
73. implement Observable fromEvent()
JavaScript
easy
358 accepted
98. validate an IP address
JavaScript
medium
333 accepted
169. LRU - Chrome storage automatic eviction
JavaScript
Algorithm
medium
307 accepted
78. convert HEX color to RGBA
JavaScript
medium
284 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
128 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