Asm.js

From APIDesign

asm.js is Mozillla's attempt to compete with performance of Google's V8 machine by defining subset of JavaScript that they will be able to execute quickly. It is another attempt to use JavaScript as another assembly language, not as a language people code directly in (use only numbers, no object structures, no callback, more weaknesses of such approach described here).

Here is an opinion from the other side - after reading bits of it I could almost admit that the intentions are not that bad.