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.

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.

Good catch. WebAssembly doesn't have access to the current time unless the JavaScript host provides it through injecting a function, so the WASM build would need to be hooked up specially to support that.

At last, I can run JavaScript in my browser. The world is now complete.

The most important thing about any new JS runtime in 2025, how do I use it from JS? /s