asm.js was not a well-behaved subset of JavaScript. It was a well-behaved subset of assembly that happened to be encoded in JavaScript. There is virtually no h

asm.js was not a well-behaved subset of JavaScript. It was a well-behaved subset of assembly that happened to be encoded in JavaScript. There is virtually no human-written JS code that is amenable to compilation to wasm in a meaningful way. At the very least, you need a (mostly) sound type system to be able to compile to wasm with a positive expected ROI. The speed of wasm comes in a large part from the fact that it is entirely statically typed, which means we don't need the speculative optimizations (and their deoptimization guards) all over the place.