Use watchers in an angular service

gistfile1.js

angular.module('app')
  .service('myService', function($rootScope) {
  
    // Inject an isolate scope into the rootscope to
    // enable us to use $watch to from a service

    this.scope = $rootScope.$new(true);
    this.scope.myService = this;

    this.scope.$watch('something', function() {});
  });