// 返回XML的Web 请求
function OnSucceededXml(executor, eventArgs)
...{
    if (executor.get_responseAvailable())
    ...{
      
        if (document.all)
            resultElementId.innerText += executor.get_xml().xml;
        else
            // Firefox
            resultElementId.textContent += "First node[首节点]: " +
                executor.get_xml().documentElement.nodeName;

    }
    else
    ...{
        if (executor.get_timedOut())
            alert("超时");
        else
            if (executor.get_aborted())
                alert("失败");
    }
}
function GetXml()
...{
    //创建WebRequest对象
    wRequest =  new Sys.Net.WebRequest();

    //设置请求文件
    wRequest.set_url("index.xml");
 
    // Set the request handler.
    wRequest.add_completed(OnSucceededXml);
   
    // Clear the results area.
   if (document.all)
        resultElementId.innerText = "";
    else
        // Firefox
        resultElementId.textContent = "";
  
    // Invoke the Web request.
    wRequest.invoke();
}
<button id="Button3" onclick="GetXml()">Xml</button>
<div id="ResultId" style="background-color:Aqua;"></div>