Someone who really understands js can pick up coffeescript in a few hours, so don't pass on a good js developer just because they haven't yet made the jump.
I don't completely agree -- I feel like CoffeeScript shares as much in common with Ruby and Python as it does with JS. I'd say a good developer would be the best fit for a CS position; depending on your deployment platform, I can almost see a case where being an embedded JS programmer might actually cause issues. If all you understand is EcmaScript, all you'll write is EcmaScript. Despite its tagline being "It's just JavaScript", it's actually much more.
I knew Python and Ruby before I started with CoffeeScript, so perhaps that colored my experience. CoffeeScript is basically a minimalized blend of js, Ruby, and Python syntax-wise. But I still think someone who understands js will pretty much automatically get CoffeeScript concept-wise, at least to the level they get js concept-wise, because the central concepts of programming in CoffeeScript aren't different than js, just the syntax.
