I have been working in JS technology for the last 5 years. From my experience in different languages and technologies this time I feel that I had made the right decision choosing to work in a Full Javascript Stack.
Working in Frontend help me to focus in the Client needs using a prototype based top-down analysis using and re-using quality code and tools.
Programming in JS at this time is really exciting. You have nice tools, frameworks and features in the language itself. With the same language you can make Mobile Apps with Ionic or React-native, Simple Page Applications with AngularJs, React or other frameworks and programming nice and beautiful code in your Backend with Express or Meteor framework. Moreover you can use a documental persistence using MongoDB or CouchDB without needing to know any SQL like language, only JS.