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JavaScript Coding Questions
As a Front-End developer, JavaScript is the core skill of everything
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1. implement curry()
JavaScript
easy
32539 accepted
3. implement Array.prototype.flat()
JavaScript
medium
24329 accepted
4. implement basic throttle()
JavaScript
Lodash
medium
17883 accepted
6. implement basic debounce()
JavaScript
Lodash
easy
17541 accepted
19. find corresponding node in two identical DOM tree
JavaScript
easy
10735 accepted
16. create an Event Emitter
JavaScript
medium
10697 accepted
11. what is Composition? create a pipe()
JavaScript
easy
9921 accepted
2. implement curry() with placeholder support
JavaScript
medium
9278 accepted
17. Create a simple store for DOM element
JavaScript
easy
8387 accepted
32. implement `Promise.all()`
JavaScript
medium
8385 accepted
14. Implement a general memoization function - `memo()`
JavaScript
medium
8376 accepted
18. Improve a function
JavaScript
easy
7620 accepted
8. can you shuffle() an array?
JavaScript
medium
7425 accepted
28. implement clearAllTimeout()
JavaScript
easy
7227 accepted
176. undefined to null
JavaScript
easy
6754 accepted
23. create a sum()
JavaScript
medium
6567 accepted
7. implement debounce() with leading & trailing option
JavaScript
Lodash
medium
6433 accepted
9. decode message
JavaScript
medium
6307 accepted
5. implement throttle() with leading & trailing option
JavaScript
Lodash
medium
6178 accepted
10. first bad version
JavaScript
Algorithm
medium
6128 accepted
167. Intersection of unsorted arrays
JavaScript
Algorithm
easy
5655 accepted
58. get DOM tree height
JavaScript
Algorithm
DOM
medium
5454 accepted
151. implement Array.prototype.map()
JavaScript
medium
5347 accepted
25. Reorder array with new indexes
JavaScript
Algorithm
easy
5284 accepted
15. implement a simple DOM wrapper to support method chaining like jQuery
JavaScript
easy
5265 accepted
162. find the single integer
JavaScript
Algorithm
easy
4824 accepted
35. implement `Promise.race()`
JavaScript
easy
4694 accepted
33. implement `Promise.allSettled()`
JavaScript
medium
4581 accepted
29. implement async helper - `sequence()`
JavaScript
medium
4558 accepted
34. implement `Promise.any()`
JavaScript
medium
4406 accepted
165. remove characters
Algorithm
medium
4386 accepted
155. create a count function
JavaScript
easy
4359 accepted
64. auto-retry Promise on rejection
JavaScript
medium
4341 accepted
159. implement promisify()
JavaScript
easy
4250 accepted
92. throttle Promises
JavaScript
medium
4029 accepted
148. create a counter object
JavaScript
easy
3938 accepted
113. Virtual DOM I
JavaScript
Algorithm
DOM
medium
3843 accepted
13. Implement a Queue by using Stack
JavaScript
Algorithm
medium
3539 accepted
161. toBe() or not.toBe()
JavaScript
medium
3519 accepted
154. Two-way binding
JavaScript
DOM
easy
3247 accepted
39. implement range()
JavaScript
easy
3244 accepted
146. implement Array.prototype.reduce()
JavaScript
medium
3103 accepted
57. create an Observable
JavaScript
medium
3096 accepted
104. Traverse DOM level by level
JavaScript
Algorithm
DOM
medium
3032 accepted
68. get DOM tags
JavaScript
Algorithm
DOM
medium
2976 accepted
91. invert a binary tree
JavaScript
Algorithm
easy
2961 accepted
30. implement async helper - `parallel()`
JavaScript
medium
2927 accepted
20. Detect data type in JavaScript
JavaScript
medium
2908 accepted
67. create your own Promise
JavaScript
medium
2878 accepted
26. implement Object.assign()
JavaScript
medium
2848 accepted
12. implement Immutability helper
JavaScript
medium
2791 accepted
37. implement Binary Search (unique)
JavaScript
easy
2735 accepted
89. Next Right Sibling
JavaScript
DOM
easy
2687 accepted
157. semver compare
JavaScript
easy
2654 accepted
31. implement async helper - `race()`
JavaScript
easy
2608 accepted
46. implement `_.once()`
JavaScript
Lodash
medium
2605 accepted
63. create `_.cloneDeep()`
JavaScript
Algorithm
Lodash
medium
2591 accepted
168. move zeros
JavaScript
Algorithm
medium
2582 accepted
60. create your own `new` operator
JavaScript
easy
2564 accepted
110. serialize and deserialize binary tree
JavaScript
Algorithm
medium
2464 accepted
47. reverse a linked list
JavaScript
Algorithm
easy
2444 accepted
40. implement Bubble Sort
JavaScript
Algorithm
easy
2388 accepted
21. implement JSON.stringify()
JavaScript
hard?
2278 accepted
145. most frequently occurring character
JavaScript
easy
2256 accepted
56. call APIs with pagination
JavaScript
medium
2251 accepted
85. implement `_.get()`
JavaScript
Lodash
medium
2178 accepted
61. create your own `Function.prototype.call`
JavaScript
medium
2166 accepted
118. Virtual DOM II - createElement
JavaScript
easy
2104 accepted
125. implement classNames()
JavaScript
medium
2082 accepted
133. roman numerals to integer
JavaScript
easy
2078 accepted
69. implement deep equal `_.isEqual()`
JavaScript
Lodash
medium
2070 accepted
123. implement Promise.prototype.finally()
JavaScript
medium
2027 accepted
103. implement Math.sqrt()
JavaScript
Algorithm
medium
2011 accepted
163. integer to roman numerals
JavaScript
Algorithm
easy
1979 accepted
81. merge sorted arrays
JavaScript
Algorithm
easy
1937 accepted
121. A number sequence
JavaScript
easy
1862 accepted
83. create an interval
JavaScript
medium
1854 accepted
107. Find the largest difference
JavaScript
Algorithm
easy
1853 accepted
105. find the first duplicate character in a string
JavaScript
string
easy
1844 accepted
38. implement `jest.spyOn()`
JavaScript
easy
1835 accepted
130. create LazyMan()
JavaScript
medium
1748 accepted
48. search first index with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1742 accepted
102. validate string of parentheses
JavaScript
Algorithm
string
easy
1716 accepted
173. uncompress string
JavaScript
string
algorithm
medium
1695 accepted
94. implement your own `Object.create`
JavaScript
easy
1691 accepted
106. Find two numbers that sum up to 0
JavaScript
Algorithm
easy
1685 accepted
53. write your own `extends` in es5
JavaScript
medium
1669 accepted
120. create `isPrime()`
JavaScript
Algorithm
easy
1668 accepted
87. longest substring with unique characters
JavaScript
Algorithm
easy
1660 accepted
138. Intersection of two sorted arrays
JavaScript
Algorithm
easy
1654 accepted
158. Previous Left Sibling
JavaScript
DOM
medium
1634 accepted
54. flatten Thunk
JavaScript
easy
1602 accepted
122. implement memoizeOne()
JavaScript
medium
1582 accepted
131. implement _.chunk()
JavaScript
Lodash
medium
1573 accepted
140. Virtual DOM III - Functional Component
JavaScript
easy
1571 accepted
86. Generate Fibonacci Number
JavaScript
Algorithm
medium
1561 accepted
97. compress a string
JavaScript
string
easy
1547 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
1418 accepted
116. implement Object.is()
JavaScript
easy
1407 accepted
109. implement `Math.pow()`
JavaScript
Algorithm
easy
1400 accepted
42. implement Insertion Sort
JavaScript
Algorithm
easy
1382 accepted
36. create a fake timer(setTimeout)
JavaScript
medium
1364 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
1251 accepted
152. Find Top k Elements
JavaScript
Algorithm
medium
1241 accepted
147. Pick up stones
JavaScript
easy
1237 accepted
55. highlight keywords in HTML string
JavaScript
Algorithm
medium
1224 accepted
100. detect circle in linked list
JavaScript
Algorithm
easy
1217 accepted
43. implement Quick Sort
JavaScript
Algorithm
medium
1215 accepted
22. implement JSON.parse()
JavaScript
medium
1201 accepted
44. implement Selection Sort
JavaScript
Algorithm
easy
1189 accepted
27. implement completeAssign()
JavaScript
medium
1179 accepted
50. search element right before target with Binary Search(possible duplicate array)
JavaScript
Algorithm
easy
1171 accepted
41. implement Merge Sort
JavaScript
Algorithm
medium
1163 accepted
101. merge identical API calls
JavaScript
medium
1142 accepted
52. create a middleware system
JavaScript
medium
1111 accepted
139. implement _.partial()
JavaScript
Lodash
medium
1093 accepted
95. implement String.prototype.trim()
JavaScript
medium
1027 accepted
82. find available meeting slots
JavaScript
Algorithm
medium
1021 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
1001 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
908 accepted
88. support negative Array index in JavaScript
JavaScript
medium
903 accepted
45. find the K-th largest element in an unsorted array
JavaScript
Algorithm
medium
902 accepted
166. validate number string
JavaScript
Algorithm
string
medium
866 accepted
117. event delegation
JavaScript
medium
849 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
108. Implement a Stack by using Queue
JavaScript
Algorithm
medium
740 accepted
177. Implement Object.groupBy()
JavaScript
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
685 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
602 accepted
172. implement `Math.clz32()`
JavaScript
medium
595 accepted
80. implement your own URLSearchParams
JavaScript
hard?
585 accepted
84. create a fake timer (setInterval)
JavaScript
medium
569 accepted
137. binary tree vertical traversal
JavaScript
Algorithm
hard?
561 accepted
71. implement Observable Subject
JavaScript
medium
543 accepted
99. extract all anchor element from HTML string
JavaScript
medium
509 accepted
72. implement Observable interval()
JavaScript
easy
504 accepted
75. implement BigInt subtraction
JavaScript
Algorithm
easy
498 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
255 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