The full Frankenstein stack is: SpiderMonkey compiled in arm emulation mode, to a WASI 0.1 module, adapted to a WASI 0.2 component, transpiled to the web with jco, running in some random WASI shim.

We do this because the JS runtime needs inline caches to be filled out before optimization, which requires an JIT and actual execution of machine code. Otherwise you just get a graph full of Unreachable. Frankly I’m amazed it works at all.