JavaScript 和 jQuery : accessing class member variables from event callback

Question

我正在编写一个 Javascript SDK 来与 Web 服务交互。我正在使用 jQuery 进行 AJAX 调用。

当 AJAX 调用失败时，我已为 ajaxError 注册了一个事件处理程序，该事件处理程序在 .js 文件顶部调用。我的问题(我不明白为什么)是，当它被调用时，我无法访问我的 Akamanda.Client 的类成员变量。

我尝试为 Akamanda.Client 添加另一种方法作为 .prototype.logError，该方法由 jQuery Ajax 处理程序调用，但即使这样， (this.logging) 的测试也失败了。

如何从 jQuery 回调访问类成员变量？我在这里不明白什么？ Akamanda.Client.logging 在 ajaxError 回调中未定义。

我的 SDK 代码:

$(document).ajaxError(function(event, jqxhr, settings, exception) {
    // more robust error handling for different conditions
    if (Akamanda.Client.logging) {
        console.log('FAILED: ' + settings.type + ' ' + settings.url + ' => ' + exception);
    }
});

Akamanda.Client = function(options) {

    this.URL = options.URL || 'http://m-test.akamanda.com';
    this.baseURL = this.URL + '/api/' + Akamanda.API_VERSION;
    this.feedsURI = '/websyndication/feed/';

    // who is the client? (iphone/android/web)
    this.clientName = options.clientName;

    // For development: Logging and buildcurl IS ON, for production: OFF
    //this.logging = options.logging || true;
    this.logging = true;

    // called when a user is not authorised (Disabled)
    // this.logoutCallback = options.logoutCallback || null;
}

Akamanda.Client.prototype.getFeeds = function(callback){
    var feeds = [];
    $.getJSON(this.baseURL + this.feedsURI, function(data) {
        $.each(data, function(index, feed) {
            feeds[index] = {
                name: feed.name,
                title: feed.title,
                link: feed.link
            };

        })
        callback(feeds);
    });//.error(function(err) { (disabled at the moment in favour of ajaxError event)
       //     console.log('Error: ' + err.error);
       // });    
}

我的客户端代码(在另一个 JS 源文件中):

var options = { logging: true };
myAPI = new Akamanda.Client(options);
var feeds = [];
var articles = [];

function getFeeds()
{
    myAPI.getFeeds(function(AkamandaFeeds) {
        feeds = AkamandaFeeds;
        showFeeds();
    });
}

Answer 1

据我从您发布的代码中看到，您从未实例化 Akamanda.Client 类型的对象。

var Client = new Akamanda.Client();

或

var Akamanda.Client = {};

Akamanda.Client.logging = ....

JSBin 示例:http://jsbin.com/ajidig/1/edit

好的，这里有一个小例子(真实的代码，但非常简化):

//we wrap our code in a self invoking function so that we don't pollute the global    namespace, see http://stackoverflow.com/questions/6715805/self-invoking-functions-javascript for further details
(function(){
     //create your object that holds all your function, that are different ways to do this
     var Akamanda = {};

     //a private function 
     function ErrorHandler(clientObj) {
          this.clientObj = clientObj;
          //do whatever with clientObj
          this.log = function(){..}
     } 
      //private constructor for clientobj
     function Client(options){
         ..
     }



     Akamanda.Client = function(){

       var newClient = new Client({..});
       //setup
       Akamanda.ErrorLogging = new ErrorHandler(newClient);
       return newClient;
     }

     //bind our service to the window object to make it accesible

     window.Akamanda = Akamanda;
})()


//client

var myAPI = Akamanda.Client();
Akamanda.ErrorLogging.log();

我希望这个基本示例有所帮助。如果你需要了解更多关于Javascript模式的知识，我可以推荐这本书http://jsninja.com/作者:John Resig，jQuery 的创建者。根据您想要做什么，还有很多框架，例如 http://backbonejs.org/这有助于处理这类事情。