A stopwatch is one of the most deceptively tricky components in frontend interviews. It looks simple — start, stop, reset — but the moment you reach for useState to track elapsed time with setInterval, you run into stale closure bugs that silently produce wrong results.
Build a fully functional stopwatch displaying elapsed time in MM:SS.cs format. Users can start, pause, and reset. The display must update at ~10ms intervals without memory leaks when the component unmounts.
The core challenge is timer management: use useRef to anchor to wall-clock time via Date.now() instead of accumulating ticks. This is a perfect question for demonstrating senior-level React timer patterns.