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 application patterns
Search, optimistic UI, pagination, forms and virtualization done right.
- 66Build search-as-you-type with debounce and
AbortControllerFree - 67Implement optimistic UI updates with rollback on failure
- 68Build infinite scrolling using
IntersectionObserver - 69Implement server-side pagination with sorting and filtering
- 70Build a controlled form with dynamic validation
- 71Implement dependent dropdowns with asynchronous options
- 72Build a reusable React modal using portals
- 73Implement an error boundary with retry/reset behavior
- 74Implement undo/redo history for a React state editor
- 75Implement a virtualized list rendering 100,000 items efficiently