If anyone wants to try out MicroQuickJS in a browser here's a simple playground interface for executing a WebAssembly compiled version of it: https://tools.simonwillison.net/microquickjs
It's a variant of my QuickJS playground here: https://tools.simonwillison.net/quickjs
The QuickJS page loads 2.28 MB (675 KB transferred). The MicroQuickJS one loads 303 KB (120 KB transferred).
Nice. Got it down from 229KB to 148KB! Thanks for the tips.
https://github.com/simonw/research/pull/5
Thats now live on https://tools.simonwillison.net/microquickjs
Thanks for sharing! The link to the PR looks like a wrong paste. I found https://github.com/simonw/tools/pull/181 which seems to be what was intended to be shared instead.
I was interested to try Date.now() since this is mentioned as being the only part of the Date implementation that is supported but was surprised to find it always returns 0 for your microquickjs version - your quickjs variant appears to return the current unix time.
The most important thing about any new JS runtime in 2025, how do I use it from JS? /s
Looks like those sizes could be improved significantly, as the builds include names etc. I would suggest linking with
emcc -O3
(and maybe even adding --closure 1 )
edit: actually the QuickJS playground looks already optimized - just the MicroQuickJS one could be improved.