code: function checkScrollBoxVisibility() {
                  self.scrollBox.horizontalBarVisible = (self.style.width !== 'auto' && dataWidth > self.scrollBox.width && self.style.overflowX !== 'hidden')
                      || self.style.overflowX === 'scroll';
                  self.scrollBox.horizontalBoxVisible = dataWidth > self.scrollBox.width;
                  self.scrollBox.verticalBarVisible = (self.style.height !== 'auto' && dataHeight > self.scrollBox.height && self.style.overflowY !== 'hidden')
                      || self.style.overflowY === 'scroll';
                  self.scrollBox.verticalBoxVisible = dataHeight > self.scrollBox.height;
              }
docs: sets actual DOM canvas element