angularjs - getting and setting value in factory in angualrjs

This is my factory:

.factory('userService',()){
  var user = {};
  return {

  getFirstname : function () {

    return user.firstname;
  },

  setFirstname : function (firstname) {
    user.firstname = firstname;
  }

}

And I'm using this service in my two controllers MainCtrl and AccountEditCtrl
I'm using my getFirstname() in my MainCtrl and setFirstname in AccountEditCtrl

.controller('MainCtrl',['userService', function(userService){
  $scope.userName = userService.getFirstName();
}]);

.controller('AccountEditCtrl',['userService', function(userService){
      userService.setFirstname("New First Name");
}]);

My problem is that when I use the userService.setFirstname() the $scope.userName don't change in MainCtrl.

Answer

In some case $watch is not working with factory object. Than you may use events for updates.

 app.factory('userService',['$rootScope',function($rootScope){
  var user = {};
  return {


  getFirstname : function () {
    return user.firstname;
  },

  setFirstname : function (firstname) {
    user.firstname = firstname;
    $rootScope.$broadcast("updates");
  }

}

}]);
app.controller('MainCtrl',['userService','$scope','$rootScope', function(userService,$scope,$rootScope) {
  userService.setFirstname("bharat");
  $scope.name = userService.getFirstname();
  $rootScope.$on("updates",function(){
    $scope.name = userService.getFirstname();
  });
}]);

app.controller('one',['userService','$scope', function(userService,$scope) {

  $scope.updateName=function(){
    userService.setFirstname($scope.firstname);
  }
}]);

Here is a working example