Pretty much everything in this comment is wrong (though I do recommend learning JavaScript before CoffeeScript)

CoffeeScript is no more of a "hack" than any compiler. Compilers take one language and turn it into another.

I think you mean Ruby syntax, not semantics. CoffeeScript's semantics are much closer to JavaScript than Ruby in almost every way.

It may have it's roots in the Ruby world, but I'd wager more non-Rubyists use CS at this point than Rubyists. I'm one of them.