[phadej]

Good comment!

I did make a too quick judgement there. It turns out you can't easily see how popularality of CoffeeScript has changed.

    It is surprising to see CoffeeScript in this list as a language compiler
    should be mainly a dev-dependency. You compile the CoffeeScript source to
    JavaScript for distribution, so you don’t need coffee-script to be a
    dependency. The packages that depend upon coffee-script include among others:
    grunt, jasmine-node, jscoverage, cucumber and hubot. They all allow you to use
    CoffeeScript sources.

While there isn't anything wrong in supporting CoffeeScript out-of-the-box, I like karma's approach more. It has "karma-coffee-preprocessor", it should be self-explanatory.