javascript - AngularJS:无法读取未定义的属性 ''

Question

我正在尝试在 AngularJS 中做这样的事情:

.factory('TranslationService', function($location, $rootScope, $routeParams, $translate, $window, tmhDynamicLocale, 
                                            LocationService, MetaService) {
      return {
        translate: function(language, translateUrlName) {

            $translate.uses(language).then(function() {

                this.translateUrl(language, translateUrlName);
            });
         },
         translateUrl: function(language, translateUrlName) {
            // do whatever
        }
      };     
    })

但我不知道为什么会出现此错误:

TypeError: Cannot read property 'translateUrl' of undefined
    at services.js:1117
    at deferred.promise.then.wrappedCallback (angular.js:6846)
    at angular.js:6883
    at Object.$get.Scope.$eval (angular.js:8057)
    at Object.$get.Scope.$digest (angular.js:7922)
    at Object.$get.Scope.$apply (angular.js:8143)
    at done (angular.js:9170)
    at completeRequest (angular.js:9333)
    at XMLHttpRequest.xhr.onreadystatechange (angular.js:9303)angular.js:5754 (anonymous function)angular.js:4846 $getangular.js:6848 deferred.promise.then.wrappedCallbackangular.js:6883 (anonymous function)angular.js:8057 $get.Scope.$evalangular.js:7922 $get.Scope.$digestangular.js:8143 $get.Scope.$applyangular.js:9170 doneangular.js:9333 completeRequestangular.js:9303 xhr.onreadystatechange

如果我只是将调用 this.translateUrl(language, translateUrlName); 移到 translate: function(language, translateUrlName) { 之外，那么它可以工作，但我不知道没有得到正确的行为。

Answer 1

Javascript 中带有闭包和 this 的标准陷阱。做:

  return {
    translate: function(language, translateUrlName) {
        var self = this;

        $translate.uses(language).then(function() {
            self.translateUrl(language, translateUrlName);
        });
     },
     translateUrl: function(language, translateUrlName) {
        // do whatever
    }
  };     
})