[rpearl]

If you translate your coffeescript to javascript serverside, then there is no overhead on Jaegermonkey or v8 (obviously).

Although I doubt that any of the browsers will ever support it directly, porting coffeescript to run directly on top of Jaegermonkey or v8 wouldn't be too hard, since there is a direct translation from coffeescript to javascript. You would only need a new front end--if you emit Spidermonkey/Hydrogen bytecode, the relevant engine can JIT it.

On a slightly related note, a friend of mine is working on this: https://wiki.mozilla.org/DevTools/Features/SourceMap

Which, while not compiling directly, will allow you to map the generated JS directly back to the coffeescript source.

[mraleph]

> if you emit Spidermonkey/Hydrogen bytecode

Hydrogen is not a bytecode, it is highlevel intermediate representation for optimizing compiler generated from AST. There is currently: 1) no frontend in V8 that accepts hydrogen in some serialized form; 2) no way to generate non-optimized (non-specialized) code from hydrogen which is quite crucial to make adaptive optimization pipeline running.