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
Hard
50 questions, 45–90 minutes each
Senior-level correctness, architecture and production constraints.
Advanced React & rendering
Reconciliation, hooks internals, concurrent rendering and SSR edge cases.
- 111Implement a minimal React-like renderer with virtual DOM diffing and keyed reconciliation
- 112Implement a mini
useStateanduseEffecthooks engineFree - 113Implement a fine-grained external state store using
useSyncExternalStorewithout tearing - 114Debug React 18 concurrent rendering inconsistencies involving mutable external data
- 115Build a React scheduler demonstrating urgent updates versus
startTransition()updates - 116Implement a virtualized grid with variable row heights, overscan, and scroll restoration
- 117Build a nested drag-and-drop tree editor with optimistic reordering
- 118Implement SSR hydration mismatch detection and a reproduction/fix exercise
- 119Build a Suspense-based data-loading example with streaming SSR boundaries
- 120Build a fault-tolerant React checkout flow with idempotent submission, recovery, and persistent state