code: function progress() {
  
                          var requestLength = $scope.getRequestLength(this.files);
  
                          this.httpRequest.upload.onprogress = function onProgress(event) {
  
                              $scope.$apply(function apply() {
  
                                  if (event.lengthComputable) {
  
                                      // Update the progress object.
                                      $scope.requestProgress.percent = Math.round((event.loaded / requestLength) * 100);
                                      $scope.requestProgress.loaded  = event.loaded;
                                      $scope.requestProgress.total   = requestLength;
  
                                  }
  
                              });
  
                          };
  
                      }
docs: Invoked each time there's a progress update on the files being uploaded.
  
  @method progress
  @return {void}