离子抛出错误模块拼写错误或忘记加载，即使正确给予它？

Question

angular.module('todo', ['ionic', 'ngCordova', 'ngMaterial', 'services']) 

这是我如何包含服务模块。 这是我的services.js文件

angular.module('services', [])
.service('UserService', function() {
// For the purpose of this example I will store user data on ionic local storage but you should save it on a database
 var setUser = function(user_data) {
  window.localStorage.starter_facebook_user = JSON.stringify(user_data);
 };

 var getUser = function(){
  return JSON.parse(window.localStorage.starter_facebook_user || '{}');
 };

 return {
 getUser: getUser,
 setUser: setUser
 };
 });

但我得到错误的模块错误或忘记加载。