A few examples of things it adds that are not widely available in JS (if at all, or requiring awkward hacks/hints in JS), off the top of my head: int64 uint32

A few examples of things it adds that are not widely available in JS (if at all, or requiring awkward hacks/hints in JS), off the top of my head: int64 uint32 popcnt copysign reinterpret_cast equivalent (the js hack for this is abysmal) pthreads SIMD AOT compilation To be fair, it's been a while since I was last one of the authors of the webassembly spec, so I could be missing some things.