[obtu]

Actually Emscripten allows you to port an existing native application to JS, and the development effort is comparable to using NaCl.

[TazeTSchnitzel]

Yup. They've ported all sorts of things with Emscripten, including, I believe, Ruby, Python and Perl.

[batista]

Yes. But it's a POC thing that's also some orders of magnitude slower...

[azakai]

It's not orders of magnitude slower, most benchmarks have it 2x-6x slower. It's rarely slower than 10x (one order of magnitude). And that is before JS engines even start to optimize for it.