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JavaScript Coding Questions
As a Front-End developer, JavaScript is the core skill of everything
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tag: JavaScript
1. implement curry()
JavaScript
easy
32629 accepted
3. implement Array.prototype.flat()
JavaScript
medium
24386 accepted
4. implement basic throttle()
JavaScript
Lodash
medium
17915 accepted
6. implement basic debounce()
JavaScript
Lodash
easy
17596 accepted
19. find corresponding node in two identical DOM tree
JavaScript
easy
10749 accepted
16. create an Event Emitter
JavaScript
medium
10709 accepted
11. what is Composition? create a pipe()
JavaScript
easy
9953 accepted
2. implement curry() with placeholder support
JavaScript
medium
9295 accepted
17. Create a simple store for DOM element
JavaScript
easy
8416 accepted
32. implement `Promise.all()`
JavaScript
medium
8406 accepted
14. Implement a general memoization function - `memo()`
JavaScript
medium
8395 accepted
18. Improve a function
JavaScript
easy
7633 accepted
8. can you shuffle() an array?
JavaScript
medium
7456 accepted
28. implement clearAllTimeout()
JavaScript
easy
7241 accepted
176. undefined to null
JavaScript
easy
6762 accepted
23. create a sum()
JavaScript
medium
6572 accepted
7. implement debounce() with leading & trailing option
JavaScript
Lodash
medium
6445 accepted
9. decode message
JavaScript
medium
6325 accepted
5. implement throttle() with leading & trailing option
JavaScript
Lodash
medium
6184 accepted
10. first bad version
JavaScript
Algorithm
medium
6148 accepted
167. Intersection of unsorted arrays
JavaScript
Algorithm
easy
5660 accepted
58. get DOM tree height
JavaScript
Algorithm
DOM
medium
5460 accepted
151. implement Array.prototype.map()
JavaScript
medium
5360 accepted
25. Reorder array with new indexes
JavaScript
Algorithm
easy
5300 accepted
15. implement a simple DOM wrapper to support method chaining like jQuery
JavaScript
easy
5280 accepted
162. find the single integer
JavaScript
Algorithm
easy
4827 accepted
35. implement `Promise.race()`
JavaScript
easy
4704 accepted
33. implement `Promise.allSettled()`
JavaScript
medium
4591 accepted
29. implement async helper - `sequence()`
JavaScript
medium
4569 accepted
34. implement `Promise.any()`
JavaScript
medium
4413 accepted
155. create a count function
JavaScript
easy
4366 accepted
64. auto-retry Promise on rejection
JavaScript
medium
4345 accepted
159. implement promisify()
JavaScript
easy
4256 accepted
92. throttle Promises
JavaScript
medium
4030 accepted
148. create a counter object
JavaScript
easy
3946 accepted
113. Virtual DOM I
JavaScript
Algorithm
DOM
medium
3849 accepted
13. Implement a Queue by using Stack
JavaScript
Algorithm
medium
3543 accepted
161. toBe() or not.toBe()
JavaScript
medium
3523 accepted
154. Two-way binding
JavaScript
DOM
easy
3254 accepted
39. implement range()
JavaScript
easy
3249 accepted
146. implement Array.prototype.reduce()
JavaScript
medium
3108 accepted
57. create an Observable
JavaScript
medium
3106 accepted
104. Traverse DOM level by level
JavaScript
Algorithm
DOM
medium
3034 accepted
68. get DOM tags
JavaScript
Algorithm
DOM
medium
2983 accepted
91. invert a binary tree
JavaScript
Algorithm
easy
2967 accepted
30. implement async helper - `parallel()`
JavaScript
medium
2942 accepted
20. Detect data type in JavaScript
JavaScript
medium
2921 accepted
67. create your own Promise
JavaScript
medium
2878 accepted
26. implement Object.assign()
JavaScript
medium
2854 accepted
12. implement Immutability helper
JavaScript
medium
2798 accepted
37. implement Binary Search (unique)
JavaScript
easy
2742 accepted
89. Next Right Sibling
JavaScript
DOM
easy
2693 accepted
157. semver compare
JavaScript
easy
2654 accepted
31. implement async helper - `race()`
JavaScript
easy
2619 accepted
46. implement `_.once()`
JavaScript
Lodash
medium
2612 accepted
63. create `_.cloneDeep()`
JavaScript
Algorithm
Lodash
medium
2596 accepted
168. move zeros
JavaScript
Algorithm
medium
2583 accepted
60. create your own `new` operator
JavaScript
easy
2567 accepted
110. serialize and deserialize binary tree
JavaScript
Algorithm
medium
2468 accepted
47. reverse a linked list
JavaScript
Algorithm
easy
2448 accepted
40. implement Bubble Sort
JavaScript
Algorithm
easy
2397 accepted
21. implement JSON.stringify()
JavaScript
hard?
2280 accepted
145. most frequently occurring character
JavaScript
easy
2258 accepted
56. call APIs with pagination
JavaScript
medium
2257 accepted
85. implement `_.get()`
JavaScript
Lodash
medium
2182 accepted
61. create your own `Function.prototype.call`
JavaScript
medium
2171 accepted
118. Virtual DOM II - createElement
JavaScript
easy
2115 accepted
125. implement classNames()
JavaScript
medium
2093 accepted
133. roman numerals to integer
JavaScript
easy
2081 accepted
69. implement deep equal `_.isEqual()`
JavaScript
Lodash
medium
2073 accepted
123. implement Promise.prototype.finally()
JavaScript
medium
2031 accepted
103. implement Math.sqrt()
JavaScript
Algorithm
medium
2012 accepted
163. integer to roman numerals
JavaScript
Algorithm
easy
1979 accepted
81. merge sorted arrays
JavaScript
Algorithm
easy
1938 accepted
121. A number sequence
JavaScript
easy
1871 accepted
83. create an interval
JavaScript
medium
1860 accepted
107. Find the largest difference
JavaScript
Algorithm
easy
1853 accepted
105. find the first duplicate character in a string
JavaScript
string
easy
1846 accepted
38. implement `jest.spyOn()`
JavaScript
easy
1840 accepted
130. create LazyMan()
JavaScript
medium
1756 accepted
48. search first index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1746 accepted
102. validate string of parentheses
JavaScript
Algorithm
string
easy
1717 accepted
173. uncompress string
JavaScript
string
algorithm
medium
1696 accepted
94. implement your own `Object.create`
JavaScript
easy
1695 accepted
106. Find two numbers that sum up to 0
JavaScript
Algorithm
easy
1685 accepted
120. create `isPrime()`
JavaScript
Algorithm
easy
1677 accepted
53. write your own `extends` in es5
JavaScript
medium
1670 accepted
87. longest substring with unique characters
JavaScript
Algorithm
easy
1660 accepted
138. Intersection of two sorted arrays
JavaScript
Algorithm
easy
1655 accepted
158. Previous Left Sibling
JavaScript
DOM
medium
1634 accepted
54. flatten Thunk
JavaScript
easy
1606 accepted
122. implement memoizeOne()
JavaScript
medium
1585 accepted
131. implement _.chunk()
JavaScript
Lodash
medium
1573 accepted
140. Virtual DOM III - Functional Component
JavaScript
easy
1572 accepted
86. Generate Fibonacci Number
JavaScript
Algorithm
medium
1563 accepted
97. compress a string
JavaScript
string
easy
1549 accepted
66. remove duplicates from an array
JavaScript
Algorithm
medium
1475 accepted
49. search last index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1423 accepted
116. implement Object.is()
JavaScript
easy
1409 accepted
109. implement `Math.pow()`
JavaScript
Algorithm
easy
1403 accepted
42. implement Insertion Sort
JavaScript
Algorithm
easy
1391 accepted
36. create a fake timer(setTimeout)
JavaScript
medium
1365 accepted
65. add comma to number
JavaScript
medium
1352 accepted
24. create a Priority Queue in JavaScript
JavaScript
Algorithm
medium
1350 accepted
156. implement `_.set()`
JavaScript
Lodash
medium
1327 accepted
135. localStorage with expiration
JavaScript
medium
1323 accepted
59. create a browser history
JavaScript
medium
1318 accepted
90. write your own `instanceof`
JavaScript
medium
1267 accepted
93. Generate Fibonacci Number with recursion
JavaScript
easy
1252 accepted
152. Find Top k Elements
JavaScript
Algorithm
medium
1241 accepted
147. Pick up stones
JavaScript
easy
1238 accepted
55. highlight keywords in HTML string
JavaScript
Algorithm
medium
1225 accepted
43. implement Quick Sort
JavaScript
Algorithm
medium
1218 accepted
100. detect circle in linked list
JavaScript
Algorithm
easy
1218 accepted
22. implement JSON.parse()
JavaScript
medium
1201 accepted
44. implement Selection Sort
JavaScript
Algorithm
easy
1193 accepted
27. implement completeAssign()
JavaScript
medium
1180 accepted
50. search element right before target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1174 accepted
41. implement Merge Sort
JavaScript
Algorithm
medium
1166 accepted
101. merge identical API calls
JavaScript
medium
1142 accepted
52. create a middleware system
JavaScript
medium
1114 accepted
139. implement _.partial()
JavaScript
Lodash
medium
1093 accepted
95. implement String.prototype.trim()
JavaScript
medium
1030 accepted
82. find available meeting slots
JavaScript
Algorithm
medium
1022 accepted
79. convert snake_case to camelCase
JavaScript
medium
1017 accepted
51. search element right after target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1004 accepted
170. Generate CSS Selector for target element
JavaScript
medium
962 accepted
96. count "1" in binary form
JavaScript
easy
936 accepted
62. implement BigInt addition
JavaScript
Algorithm
easy
914 accepted
88. support negative Array index in JavaScript
JavaScript
medium
907 accepted
45. find the K-th largest element in an unsorted array
JavaScript
Algorithm
medium
903 accepted
166. validate number string
JavaScript
Algorithm
string
medium
866 accepted
117. event delegation
JavaScript
medium
850 accepted
136. find median of two sorted array
JavaScript
Algorithm
medium
834 accepted
149. interpolation
JavaScript
medium
807 accepted
111. Count palindromic substrings
JavaScript
Algorithm
string
medium
752 accepted
177. Implement Object.groupBy()
JavaScript
medium
744 accepted
108. Implement a Stack by using Queue
JavaScript
Algorithm
medium
740 accepted
132. the angle between hour hand and minute hand of a clock
JavaScript
medium
707 accepted
142. lit-html 1 - tagged templates
JavaScript
lit-html
easy
706 accepted
119. create a tokenizer
JavaScript
medium
689 accepted
112. remove duplicate characters in a string
JavaScript
Algorithm
string
medium
641 accepted
134. create your own Cookie
JavaScript
medium
632 accepted
153. uglify CSS class names
JavaScript
medium
612 accepted
70. implement Observable.from()
JavaScript
medium
607 accepted
172. implement `Math.clz32()`
JavaScript
medium
595 accepted
80. implement your own URLSearchParams
JavaScript
hard?
587 accepted
84. create a fake timer (setInterval)
JavaScript
medium
570 accepted
137. binary tree vertical traversal
JavaScript
Algorithm
hard?
561 accepted
71. implement Observable Subject
JavaScript
medium
549 accepted
99. extract all anchor element from HTML string
JavaScript
medium
509 accepted
72. implement Observable interval()
JavaScript
easy
506 accepted
75. implement BigInt subtraction
JavaScript
Algorithm
medium
500 accepted
171. create callback on message channel
JavaScript
medium
496 accepted
164. implement Immer produce()
JavaScript
medium
488 accepted
74. implement Observable Transformation Operators
JavaScript
easy
451 accepted
73. implement Observable fromEvent()
JavaScript
easy
436 accepted
98. validate an IP address
JavaScript
medium
411 accepted
169. LRU - Chrome storage automatic eviction
JavaScript
Algorithm
medium
389 accepted
78. convert HEX color to RGBA
JavaScript
medium
356 accepted
143. Virtual DOM IV - JSX 1
JavaScript
medium
314 accepted
141. implement btoa()
JavaScript
easy
286 accepted
124. calculate arithmetic expression
JavaScript
Algorithm
medium
259 accepted
76. implement BigInt addition with sign
JavaScript
medium
236 accepted
160. implement atob()
JavaScript
medium
200 accepted
114. implement BigInt multiplication
JavaScript
medium
179 accepted
144. serialize and deserialize data types not supported in JSON
JavaScript
medium
176 accepted
150. Virtual DOM V - JSX 2
JavaScript
medium
167 accepted
77. implement BigInt subtraction with sign
JavaScript
medium
140 accepted
115. implement BigInt division
JavaScript
medium
86 accepted
126. BigDecimal addition
JavaScript
Algorithm
medium
82 accepted
174. CSS Grid Layout auto-placement algorithm - sparse
JavaScript
CSS
hard?
59 accepted
128. BigDecimal multiplication
JavaScript
Algorithm
medium
46 accepted
129. BigDecimal Division
JavaScript
Algorithm
medium
44 accepted
127. BigDecimal subtraction
JavaScript
Algorithm
medium
39 accepted
175. CSS Grid Layout auto-placement algorithm - dense
JavaScript
CSS
medium
21 accepted