code: function(dx, dy) {
  
              if (dx === undefined) {
                  dx = 0;
              }
  
              if (dy === undefined) {
                  dy = dx;
              }
  
              this.x -= dx;
              this.y -= dy;
              this.width += 2 * dx;
              this.height += 2 * dy;
  
              return this;
          }
docs: inflate by dx and dy, recompute origin [x, y] @param dx {delta_x} representing additional size to x @param dy {delta_y} representing additional size to y - dy param is not required -> in that case y is sized by dx