2 JavaScript Stopwatches

Build a precise JavaScript stopwatch from scratch, mastering core time-based logic. The key technique shown here isn’t just a simple counter; it uses setInterval to trigger UI updates. On each tick, the elapsed time is accurately calculated by subtracting a stored start timestamp from the current Date.now(). This approach ensures the timer doesn’t drift and makes implementing robust start, stop, and reset functionality straightforward. These demos cover state management, formatting milliseconds into a readable display, and direct DOM manipulation - all with pure, dependency-free JavaScript.

Last updated: December 25, 2025