AngularJS - Injecting factory from another module into a provider

Question

I have a factory from a separate module that I would like to inject into a provider for my module, but I keep getting unknown provider errors. What am I doing wrong?

What I would like to inject:

var angularSocketIO = angular.module('socketioModule', []);
angularSocketIO.factory('socketio', [
    '$rootScope', 
    'addr', 
    function($rootScope, addr) {
        var socket = io.connect(addr,{
            'sync disconnect on unload': true
        });
                ...
        return socket;
    }
]);

Where I am trying to inject it:

angular.module('myApp.services', ['socketioModule'])
    .provider('greeter', ['socketio', function(socket) {
        var salutation = 'Hello';
        this.setSalutation = function(s) {
            salutation = s;
        }

        function Greeter(a) {
            this.salutation = salutation;
            socket._emit('hello')

            this.greet = function() {
                return salutation + ' ' + a;
            }
        }

        this.$get = function(version) {
            return new Greeter(version);
        };
    }]);

That results in

Error: [$injector:modulerr] Failed to instantiate module myApp due to:
[$injector:modulerr] Failed to instantiate module myApp.services due to: 
[$injector:unpr] Unknown provider: socketio

Answer 1

I think is because all the providers are instantiated before the factories and so a provider has to depend only on other providers.

As a way around that, I am using the injector method of angular.module to create the module. A plunker that should do what you were trying to accomplish: http://plnkr.co/edit/g1M7BIKJkjSx55gAnuD2

Notice that I changed also the factory method. The factory method is now returning an object with a connect method.

var angularSocketIO = angular.module('socketioModule', ['ng']);
angularSocketIO.factory('socketio', [
    '$rootScope',
    function($rootScope) {
      return {
        connect: function(addr) {
          var socket = io.connect(addr, {
            'sync disconnect on unload': true
          });

          return socket;
        }
      };
    }]);


  angular.module('myApp.services', ['socketioModule'])
  .provider('greeter', [
    function() {
      var injector = angular.injector(['socketioModule']);
      var socketio = injector.get('socketio');

      var salutation = 'Hello';
      this.setSalutation = function(s) {
        salutation = s;
      }

      function Greeter(a) {
        this.salutation = salutation;
        socket._emit('hello');

        this.greet = function() {
          return salutation + ' ' + a;
        };
      }

      this.$get = function(version) {
        return new Greeter(version);
      };
    }
  ]);


  var myApp = angular.module('myApp', ["myApp.services"]);

Answer 2

I think you can add dependencies via $get method in provider:

angular.module('myApp.services', ['socketioModule'])
  .provider('greeter', [
    function() {
        ...
        this.$get = ['socketio', function(socket, version) {
            function Greeter(a) {
                  this.salutation = salutation;
                  socket._emit('hello')

                  this.greet = function() {
                      return salutation + ' ' + a;
                  }
             }
             return new Greeter(version);
      }];
   }  
]);