Ayuda explotar uploader en AJAX

var http = createRequestObject();
var uploader = '';

function createRequestObject() {
    var obj;
    var browser = navigator.appName;
    
    if(browser == "Microsoft Internet Explorer"){
        obj = new ActiveXObject("Microsoft.XMLHTTP");
    }
    else{
        obj = new XMLHttpRequest();
    }
    return obj;    
}

function traceUpload(uploadDir) {
         
   http.onreadystatechange = handleResponse;

   http.open("GET", 'sube_archivo.php?uploadDir='+uploadDir+'&uploader='+uploader); 
   http.send(null);   
}

function handleResponse() {

    if(http.readyState == 4){
        document.getElementById(uploaderId).innerHTML = http.responseText;
        //window.location.reload(true);
    }
    else {
        document.getElementById(uploaderId).innerHTML = "Uploading File. Please wait...";
    }
}

function uploadFile(obj) {
    var uploadDir = obj.value;
    uploaderId = 'uploader'+obj.name;
    uploader = obj.name;
    
    document.getElementById('formName'+obj.name).submit();
    traceUpload(uploadDir, obj.name);    
}