[ybx]

Someone in Mozilla came up with a language called LLJS, that took full advantage of and compiled down to asm.js.

It looked like it had some promise, since it wasn't nearly as heavy as emscripten, but I don't think much has happened with it since it was created.

[pippy]

Interesting, I've only ever known about Emscripten based asm.js compilers. TypeScript + LLVM have the benefit of being actively developed with a strong community backing.