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 brow

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 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.