然后()不起作用(那么不是函数)

I have a little problem developing a simple GUI for a game idea using AngularJS (v1.3.15) and Angular-Route. Anyway, for the registration, i want to pre-check the availability for the username while being typed. I set up a $watch, call the factory service to get an $http.post answer, but in my controller, I get the error "I have a little problem developing a simple GUI