code: function() {
          if (this.defaultZoomLevel) {
              return this.defaultZoomLevel;
          }
  
          var aspectFactor = this._contentAspectRatio / this.getAspectRatio();
          var output;
          if (this.homeFillsViewer) { // fill the viewer and clip the image
              output = aspectFactor >= 1 ? aspectFactor : 1;
          } else {
              output = aspectFactor >= 1 ? 1 : aspectFactor;
          }
  
          return output / this._contentBounds.width;
      }
docs: Returns the home zoom in "viewport zoom" value.
  @function
  @returns {Number} The home zoom in "viewport zoom".