code: function updateViewport() {
  	const viewport = {};
  	viewport.top = window.scrollY;
  	viewport.left = window.scrollX;
  	viewport.width = window.innerWidth;
  	viewport.height = window.innerHeight;
  	viewport.right = viewport.left + viewport.width;
  	viewport.bottom = viewport.top + viewport.height;
  
  	debug( 'viewport: %o', viewport );
  	return viewport;
  }
docs: inspired by https://github.com/jkroso/viewport