我正在开发一个从通过AJAX网络获取数据的部件，我想提供一个错误信息，如果该部件无法连接到服务器。我做与jQuery的Ajax对象，它提供了一个错误回调函数的要求，但在没有互联网连接，只有在提出要求但没有其他原因，它不叫。

现在如何检查计算机是否连接到互联网？

解决方案

更新：由于您要创建一个Dashboard小工具，我跑了多次试验

我发现， $。阿贾克斯调用实际上触发了一个错误，当没有互联网连接。于是我就约了巨大的成功手动创建XMLHTT prequest对象。如果你需要JSON解析，我建议也包括 json2.js 解析器。

的事情我没有做这项工作：的

在控件属性在短跑code，我点击允许网络访问（如果你使用的不是短跑code，检查的文档进行适当的plist设置扭转这一上） 我用下面的code：

VAR XHR =新XMLHtt prequest（）;
xhr.addEventListener（'readystatechange'，state_change，真正的）;
xhr.open（GET，URL，真正的）;
xhr.send（空）;

功能state_change（）{
   如果（xhr.readyState == 4）{
        如果（xhr.status == 200）{
          的console.log（'工作'）; //只有当运行在短跑code工作
          //使用xhr.responseText或JSON.parse（xhr.responseText）
        }否则，如果（xhr.status == 0）{
          的console.log（'没有互联网'）; //只有当运行在短跑code工作
        } 其他 {
          //其他错误
        }
   }
}

/结束更新

我编辑我的回答your原来的问题因为你在评论中问它。评论后，我看到你贴了这个问题。

总之，添加暂停参数给你的 $。阿贾克斯呼叫并将其设置为较小的数字（像5000毫秒）。您的误差函数将请求超时后调用。

i'm developing a widget that is fetching data from the internet via ajax and i want to provide a error message, if the widget cannot connect to the server. i'm doing the request with jquery's ajax object which provides a error callback function, but it's not called when there is no internet connection, only if the request is made but fails for other reasons.

now how can i check if the computer is connected to the internet?

解决方案

UPDATE: Since you are creating a Dashboard widget, I ran a number of tests.

I found that the $.ajax call actually triggered an error when there was no internet connection. So I went about creating a XMLHTTPRequest object manually with great success. If you need JSON parsing, I suggest also including the json2.js parser.

Things I did to make this work:

In Widget Attributes in Dashcode I clicked "Allow Network Access" (If you aren't using Dashcode, check the docs for the proper plist setting to turn this on) I used the following code:

var xhr = new XMLHttpRequest();
xhr.addEventListener('readystatechange', state_change, true);
xhr.open("GET", url, true);
xhr.send(null);

function state_change(){
   if(xhr.readyState == 4){
        if(xhr.status == 200){
          console.log('worked'); // Only works if running in Dashcode
          // use xhr.responseText or JSON.parse(xhr.responseText)
        } else if(xhr.status == 0) {
          console.log('no internet'); // Only works if running in Dashcode
        } else {
          // Some other error
        } 
   }
}

/End Update

I answered this by editing my answer to your original question since you asked it in the comments. After commenting I saw you posted this question.

To summarize, add the timeout parameter to your $.ajax call and set it to a low number (like 5000 milliseconds). Your error function will be called after the request times out.