Let's see. So right now, I can build apps on the desktop using Roger Wang's node-webkit, write server-side code that just works without fiddling with 18 layers of config and absurdly over-complicated servers that refuse to just do the 'duh' things right out of the box, write phonegap/cordova apps for Android, IOS, Winphone, and several other platforms simultaneously including desktop mostly reusing the same code in Roger Wang's node-webkit (highly recommend btw - thanks Roger). I can write Linux GUIs in JS. I can do damn near anything Microsoft using web technology...
So uh... yes. I would say the answer is yes. But it's not just JS. If you really want to be able to handle UI well, you have to learn the crap out of CSS. Once the crap has been learned out of, you can do damn near anything including performance critical-stuff with a little help from our friends C and C++ bound easily to JS through V8.
And you can't be a Java dev about it and write once and test nowhere. You do actually have to learn the quirks of the platforms you're supporting. There is no multi-platform solution that has negated that but I would argue that web technology and web UI devs have taught the planet how to finally !@#$ing do it right.
As far as I'm concerned, and I've been exposed to PHP, Python, C#, Java, and Ruby professionally, no language as popular and widespread wraps, adapts and normalizes as well as JS. Nothing. This may have something to do with why it has spread from the client-side browser like wildfire and you're finding yourself irritated that you keep running into it all over the place.