Simple way to cache the information about the logged in user, using an AngularJS service

app.js

/** This file serves as a usage example **/
angular.module("MyApp").controller("homeCtrl", ["$scope", "$rootScope", "UserService", homeCtrl]);

function homeCtrl($scope, $rootScope, UserService) {
   UserService.GetUser().then(function(user) {
       console.log( user.FirstName );
   }, function() {
       console.log( 'An error occurred' );
   });
}

userSvc.js

angular.module("MyApp")
    .factory("UserService", ["$http", "$rootScope", "$q", UserService]);

function UserService($http, $rootScope, $q, API_URL) {
    return {
        //Function returns a promise either way, 
        // so calling functions have no idea if we're calling the database or not. 
        // This allows for handy caching.
        var loadingUser = false;
        GetUser: function() {
            if (!$auth.isAuthenticated()) {
                deferred.reject("User is not signed in.");
            }
            else if ($rootScope.user) {
                deferred.resolve(
                    $rootScope.user);
            } else if (loadingUser) {
                return deferred.promise;
            } else {
                loadingUser = true;
                $http.get(API_URL + "users/0").then(function(user) {
                    $rootScope.user = user.data;
                    loadingUser = false;
                    deferred.resolve($rootScope.user);
                }, function(error) {
                    // Very important that we release the resource! 
                    loadingUser = false;
                    deferred.reject(error.data);
                });
            }
            return deferred.promise;
        },
    }
}