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
Medium
75 questions, 25–45 minutes each
Implement, then defend your edge cases, performance and tests.
React hooks & state
Custom hooks without stale closures, plus a store built from first principles.
- 56Implement
useDebounce()for values - 57Implement
useThrottle()for values and callbacks - 58Implement
usePrevious()without causing an additional render - 59Implement
useInterval()without stale closuresFree - 60Implement
useLocalStorage()with serialization and cross-tab updates - 61Implement
useFetch()with loading, error, and cancellation - 62Implement
useQuery()with caching, retries, and stale data - 63Implement
useIntersectionObserver()for lazy loading - 64Implement a small Redux-style store using subscriptions and reducers
- 65Debug an infinite
useEffect()loop and prevent stale asynchronous responses