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.
15 of 150 questions
Medium
75 questions, 25–45 minutes each
Implement, then defend your edge cases, performance and tests.
Browser, network & performance
Fetch wrappers, routers, workers, caching and Web Vitals in practice.
- 86Implement a fetch wrapper with timeout and
AbortControllerFree - 87Implement request and response interceptors similar to Axios
- 88Implement retry with exponential backoff and jitter
- 89Implement a basic client-side router using the History API
- 90Implement synchronization between browser tabs using
BroadcastChannel - 91Implement browser storage with TTL and schema-version migration
- 92Build a lazy image loader using
IntersectionObserver - 93Implement an accessible focus trap for a dialog
- 94Implement an analytics SDK with event batching and
sendBeaconfallback - 95Implement a Web Worker for CPU-intensive computation
- 96Implement a simple Service Worker caching strategy
- 97Implement a responsive masonry layout using measured item heights
- 98Implement a DOM-based text highlighter that preserves existing markup
- 99Build a lightweight client-side search index for 10,000 records
- 100Implement a performance monitor measuring Web Vitals and reporting metrics