Well, that and Emscripten[1], which is the tool Mozilla used to bring Unreal Engine 3 into the web[2].

Note taht Emscripten is actually entitled An LLVM-to-JavaScript Compiler

[1] https://github.com/kripken/emscripten

[2] https://blog.mozilla.org/blog/2013/03/27/mozilla-is-unlockin...