[skybrian]

You need to look at serialization overhead for exchanging data. For example, I don't think web assembly has direct access to JavaScript strings? What about JSON?

Seems like you're either converting a lot of strings (which wastes memory) or calling lots of JavaScript string methods from web assembly, which is not likely to be fast in an inner loop.

[cormacrelf]

To be clear, I haven't done anything serious in WASM that would hit any limits here.