用XMLHTTPRequest获取网页源代码的疑问？

JScript code

function addLoadEvent(func){    var oldonload=window.onload;    if(typeof window.onload!='function'){        window.onload=func;    }else{        window.onload=function(){            oldonload();            func();        }    }}addLoadEvent(doth);    var READY_STATE_UNINITIALIZED=0;var READY_STATE_LOADING=1;var READY_STATE_LOADED=2;var READY_STATE_INTERACTIVE=3;var READY_STATE_COMPLETE=4;            var req=null;var console=null;                         function sendRequest(url,params,HttpMethod){    if(!HttpMethod){        HttpMethod="GET";    }    req=initXMLHTTPRequest();    if(req){        req.onreadystatechange=onReadyStateChange;        req.open(HttpMethod,url,true);        req.setRequestHeader("Content-Type","application/x-www-form-urlencoded");        req.setRequestHeader("Pragma", "no-cache");                req.send(params);    }}function initXMLHTTPRequest(){        var xRequest=null;    if(window.XMLHttpRequest){        xRequest=new XMLHttpRequest();    }else if(typeof ActiveXObject!="undefined"){        xRequest=new ActiveXObject        ("Microsoft.XMLHTTP");    }    return xRequest;}function onReadyStateChange(){    var ready=req.readyState;    check=req.readyState;    var data=" ";    if(ready==READY_STATE_COMPLETE){        data=req.responseText;                }    toConsole(data);}function toConsole(data){    if(console!=null){        var newline=document.createElement("div");        newline.id="comedata";        console.appendChild(newline);        var txt=document.createTextNode(data);        newline.appendChild(txt);            }}function doth(){    console=document.getElementById('console');    sendRequest("data.txt")}

获取本地data.txt里的内容一切正常。
我将data.txt换成url为什么显示的结果是一片空白呢？

[解决办法]
楼主参照下

http://blog.csdn.net/yixinpai/article/details/6045094
[解决办法]
这个用后台做

参考下
http://uicss.cn/cross-domain/