code: function(numberOfDownloaded, finishCallback, allCompletedCallback) {
      let downloadedItem = 0;
      return zincGeometry => {
        downloadedItem = downloadedItem + 1;
        if (finishCallback != undefined && (typeof finishCallback == 'function'))
          finishCallback(zincGeometry);
        if (downloadedItem == numberOfDownloaded)
          if (allCompletedCallback != undefined && (typeof allCompletedCallback == 'function'))
            allCompletedCallback();
      };
    }
docs: Object to keep track of number of items downloaded and when add items are downloaded allCompletedCallback is called