The Must-Solve 150.
Every question is a real implementation, debugging or architecture task. Work through the levels in order, or jump straight to what your next interview needs.
10 of 150 questions
Easy
25 questions, 10–20 minutes each
Warm-ups you should solve without help.
JavaScript fundamentals
Rebuild the core array and function methods every interviewer expects you to know cold.
- 1Implement
Array.prototype.map() - 2Implement
Array.prototype.filter() - 3Implement
Array.prototype.reduce() - 4Implement
Function.prototype.call() - 5Implement
Function.prototype.apply() - 6Implement
Function.prototype.bind(), including partial argumentsFree - 7Implement a
once()function using closures - 8Implement a function to flatten a nested array
- 9Implement
groupBy()for an array of objects - 10Implement
get(object, "a.b.c")with a default value