add-progress-bar-afu.js

xhr: function() {
    var xhr = new window.XMLHttpRequest();
    xhr.upload.addEventListener("progress", function(evt){
      if (evt.lengthComputable) {
        var percentComplete = evt.loaded / evt.total;
        percentComplete = (percentComplete.toFixed(2) * 100);
        // add a progress bar container
        if ( $('#upload-progress',container).length == 0 ) {
        	$(container).append('<div id="upload-progress" style="background: rgba(255, 186, 186, 0.32); width: 0; overflow: hidden; padding: 4px;"></div>');
        }
        $('#upload-progress',container).css({
        	width: percentComplete + '%'
        });

      }
    }, false);
    return xhr;
}