JAVASCRIPT

xhr.upload

var xhr = $.ajaxSettings.xhr();
if (xhr.upload) {
    xhr.upload.addEventListener('progress', function(event) {
        var percent = 0;
        var position = event.loaded || event.position;
        var total = event.total;
        if (event.lengthComputable) {
            percent = Math.ceil(position / total * 100);
        }
        updateProgressBar(percent);
    }, false);
}
return xhr;