FWIW, I used js2coffee on a 400-line JS file powering an app today and the compiled version of the code (js->coffee->js) was noticeably faster than the straight JS version. The for-in efficiency is probably part of that.

A quick way to port once: http://ricostacruz.com/js2coffee/

agree. I've never really considered anything about Javascript's syntax to be cumbersome. I've written server-side Ruby and appreciate the syntax...

But two points:

1) The syntax wasn't the only thing that drew me to Ruby. 2) I just don't see an any real need morph my JS code into a similar syntax. Writing JS is pretty easy.