Not a big fan of ditching Ruby, since I've spent the last four years learning it. But, progress is progress.
The thing about JavaScript is that it's a prototyped language. If you're coding in it "properly," it's a little... odd, compared to other, similar languages.
To anyone scared about scripting being HTML5 only, don't worry. Just like anyone can include a Ruby interpreter in their engine, they can also include a JavaScript interpreter too. Unity has had its own JavaScript interpreter for a while now, and it makes Windows/Mac/Linux executables.