Show HN: Neko.js, a recreation of the first virtual pet (opens in new tab)

Hi HN,

Best wishes for the new year!

Here is a late Christmas present: I rebuilt Neko [1], the classic desktop cat that chases your mouse, as a tiny, dependency-free JavaScript library that you can embed directly in your webpages (for example I put it on my personal blog).

Live demo: https://louisabraham.github.io/nekojs/

GitHub: https://github.com/louisabraham/nekojs

Drop-in usage is a single script tag:

    <script src="https://louisabraham.github.io/nekojs/neko.js" data-autostart></script>

This is a fairly faithful recreation of Neko98: same state machine, same behaviors, same original 32×32 pixel sprites. It follows your cursor, falls asleep when idle, claws walls, and you can click it to cycle behavior modes.

What made this project interesting to me is how I built it. I started by feeding the original C++ source (from the Wayback Machine) to Claude and let it "vibe code" a first JS implementation. That worked surprisingly well as a starting point, but getting it truly accurate required a lot of manual fixes: rewriting movement logic, fixing animation timing, handling edge cases the AI missed, etc.

My takeaway: coding agents are very useful at resurrecting old codebases, and this is probably the best non-soulless use of AI for coding. It gets you 60–70% of the way there very fast, especially for legacy code that would otherwise rot unread. The last 30% still needs a human who cares about details.

The final result is ~38KB uncompressed (~14KB brotli), zero dependencies, and can be dropped into a page with a single <script> tag.

Happy to hear thoughts from desktop pets nostalgics!

[1]: https://en.wikipedia.org/wiki/Neko_(software)