这个`checkSession`函数有什么作用？

Question

我已将firebase和angularfire库包含在我的离子框架项目中。

我正在关注我的示例项目的以下链接。 https://www.sitepoint.com/creating-firebase-powered-end-end-ionic-application/

我无法理解下面'app.js'中的'checkSession'功能是如何工作的。有人可以解释一下吗？

我们如何调用'checkSession'函数内的'auth'函数？

app.js

angular.module('bucketList', ['ionic', 'firebase', 'bucketList.controllers'])

.run(function($ionicPlatform, $rootScope, $firebaseAuth, $firebase, $window, $ionicLoading) {
  $ionicPlatform.ready(function() {
    // Hide the accessory bar by default (remove this to show the accessory bar above the keyboard
    // for form inputs)
    if (window.cordova && window.cordova.plugins.Keyboard) {
      cordova.plugins.Keyboard.hideKeyboardAccessoryBar(true);
    }
    if (window.StatusBar) {
      StatusBar.styleDefault();
    }

    $rootScope.userEmail = null;
    $rootScope.baseUrl = 'https://bucketlist-app.firebaseio.com/';
    var authRef = new Firebase($rootScope.baseUrl);
    $rootScope.auth = $firebaseAuth(authRef);

    $rootScope.show = function(text) {
      $rootScope.loading = $ionicLoading.show({
        content: text ? text : 'Loading..',
        animation: 'fade-in',
        showBackdrop: true,
        maxWidth: 200,
        showDelay: 0
      });
    };

    $rootScope.hide = function() {
      $ionicLoading.hide();
    };

    $rootScope.notify = function(text) {
      $rootScope.show(text);
      $window.setTimeout(function() {
        $rootScope.hide();
      }, 1999);
    };

    $rootScope.logout = function() {
      $rootScope.auth.$logout();
      $rootScope.checkSession();
    };

    $rootScope.checkSession = function() {
      var auth = new FirebaseSimpleLogin(authRef, function(error, user) {
        if (error) {
          // no action yet.. redirect to default route
          $rootScope.userEmail = null;
          $window.location.href = '#/auth/signin';
        } else if (user) {
          // user authenticated with Firebase
          $rootScope.userEmail = user.email;
          $window.location.href = ('#/bucket/list');
        } else {
          // user is logged out
          $rootScope.userEmail = null;
          $window.location.href = '#/auth/signin';
        }
      });
    }
  });
})