code: function(features) {
              var result = [];
              features.forEach(function(feature) {
                  if (feature == 'volume') {
                      result.push(this.getSignedVolume());
                  } else if (feature == 'area') {
                      result.push(this.getArea());
                  }
              }, this);
              return result;
          }
docs: accepts array of features to calculate returns array of results