Ajax错误，我实在看不出哪里的问题

复制内容到剪贴板

代码:

function getHttpObject(){
    try{ return new XMLHttpRequest();}catch(e){}
    try{ return new ActiveXObject('Msxml2.XMLHTTP.6.0');}catch(e){}
    try{ return new ActiveXObject('Msxml2.XMLHTTP.4.0');}catch(e){}
    try{ return new ActiveXObject('Msxml2.XMLHTTP.3.0');}catch(e){}
    try{ return new ActiveXObject('Msxml2.XMLHTTP');}catch(e){}
    try{ return new ActiveXObject('MSXML3.XMLHTTP');}catch(e){}
    try{ return new ActiveXObject('MSXML.XMLHTTP');}catch(e){}
    try{ return new ActiveXObject('Microsoft.XMLHTTP');}catch(e){}
    try{ return new ActiveXObject('MSXML2.ServerXMLHTTP');}catch(e){}
    return null;
}
function getNewContent(){
    var request =getHttpObject();
    request.open("GET","example.txt",true);
    if(request) {
        request.onreadystatechange = function(){
            if(request.readyState == 4 && request.status == 200){
                var para = document.createElement("p");
                var txt = document.createTextNode(request.responseText);
                para.appendChild(txt);
                document.getElementById("new").appendChild(para);
            }
        };
        
        request.overrideMimeType('text/plain; charset=x-user-defined');
        request.setRequestHeader('Content-Type', 'text/plain');
        request.send(null);
    }else {
        alert('Sorry, your browser doesn\'t support XMLHttpRequest');
    }
}
addLoadEvent(getNewContent);