window.addEventListener("loade",initall,false);
var xhr=false;/*一个XMLHttpRequest对象*/
function initall(){
    document.getElementById("txtDemo").addEventListener("click",getNewFile,false);
}
function getNewFile(event){/*获取文件的信息*/
    makeRequest(this.href);
    event.preventDefault();
}
function makeRequest(url){
    /*兼容大多数浏览器*/
    if(window.XMLHttpRequest){
        xhr=new XMLHttpRequest();
    }
    else{
        if(window.ActiveXObject){
            try {
                xhr=new ActiveXObject("Microsoft.XMLHTTP")
            } catch (error) {
                
            }
        }
    }
    if(xhr){
        xhr.addEventListener("readystatechange",showContents,false);
        xhr.open("GET",url,true);
        xhr.send(null);
    }
    else{
        document.getElementById("updateArea").innerHTML="Sorry";
    }
}
function showContents(){
    if(xhr.readyState==4){
        if(xhr.status==200){
            if(xhr.responseXML&&xhr.responseXML.childNodes.length>0){
                var outMsg=getText(xhr.responseXML.getElementByTagName('choices')[0]);/*对于xml格式的文件需要有choices标签*/
            }
            else{
                var outMsg=xhr.responseText;/*如果是txt文件，就直接返回这个文件的内容*/
            }
        }
        else{
            var outMsg="There is some problem with the request"+xhr.status;
        }
        document.getElementById("updateArea").innerHTML=outMsg;
    }
    function getText(inval){
        if(inval.textContent){/*检测这个有没有textContent属性*/
            return inval.textContent;
        }
        return inval.text;
    }
}