Nice, I had a crack at doing this a while back using emscripten, but couldn't get around that Vim's input handling is blocking.

Looks like coolwanglu has found a way around this by hacking some kind of async transformation into emscripten. I haven't looked at his code, but I suspect he specially handles known blocking libc calls. My guess is some how storing the set of stack frames when a blocking function is called so that the stack can be unwound to let the js engine continue.

Good stuff.