Javascript Ajax异步读取RSS文档具体实现

function createXHR(url){
     if(window.XMLhttprequest){
         xmlhttp = new XMLhttprequest();
     }else{ 
       xmlhttp = new ActiveXObject("Microsoft.XMLhttp");
    }
    xmlhttp.open("post",url,"false");
    xmlhttp.onreadystatechange = getResponse;     xmlhttp.setrequestHeader("Content-type","application/x-www-form-urlencoded");
    xmlhttp.send(null);
 }

function readDoc(doC){
    root = doc.getElementsByTagName("chAnnel")[0];
    doctitle = root.getElementsByTagName("title")[0];
    docLink = root.getElementsByTagName("link")[0];
    docDescription = root.getElementsByTagName("description")[0];
    items = root.getElementsByTagName("item");
    for(var i=0;i<items.length;i++){
        itemtitle = items[i].getElementsByTagName("title")[0];
        itemLink = items[i].getElementsByTagName("link")[0];
        itemDescription = items[i].getElementsByTagName("description")[0];
        //itemPubDate = items[i].getElementsByTagName("pubDate")[0];
        document.getElementById("rsstitle").innerHTML = doctitle.firstChild.nodeValue;
        temp = "</h1><h2><a href=""+itemLink.firstChild.nodeValue+"" target="_blank">"+itemtitle.firstChild.nodeValue+"</a></h2>"+"<p>"+itemDescription.firstChild.nodeValue+"</p><hr/>";
        document.getElementById("readRss").style.display = "none";
        document.getElementById("printRss").getElementsByTagName("span")[0].style.display = "none";
        document.getElementById("printRss").innerHTML = document.getElementById("printRss").innerHTML + temp;
    }
}

createXHR("http://www.apple.com.cn/hotnews/rss/hotnews.rss");

function getResponse(){
   if(xmlhttp.readyState == 4){     
        if(xmlhttp.status == 200){ 
            rssDoc = xmlhttp.responseXML;
            readDoc(rssDoc);//调用readDoc()函数
        }else{
            document.getElementById("rsstitle").innerHTML = "读取异常！";
            //alert(xmlhttp.status);
        }
    }
}