JavaScript is broad, you can use it on the client and on the server. You will probably need to learn a front-end framework (just pick one, don't bother too much on picking the right one) - AngularJS, React are both very good choices. With this and some HTML/CSS knowledge you can build a pretty cool static app.
Meteor[1] gives you some server-side capabilities. The JAWS[2] framework does the same but in an AWS environment. I'm also working on a project called Sync Ninja[3] that will be like those two but un-opinionated (though it's not ready yet). You can of course use pure Node.js on the server if you want.
[1] https://github.com/meteor/meteor [2] https://github.com/jaws-framework/JAWS [3] https://github.com/syncninja/syncninja