the loop calculating the header/body/footer column widths is forcing CSS reflows in a loop
https://github.com/zkoss/zk/blob/v8.5.2.1/zul/src/archive/web/js/zul/mesh/MeshWidget.js#L865-L874

reading offsetWidth after a style update forces CSS reflows (especially expensive when there are many columns)

this is avoidable by caching the offsetWidths before adjusting the styles

e.g.:

			var cachedOffsetWidths = {};
			for (var w = head.firstChild, bodyCol = bdcol; w && bodyCol; w = w.nextSibling) {
			    cachedOffsetWidths[w.uuid] = w.$n().offsetWidth;
				bodyCol = bodyCol.nextSibling;
			}

			for (var w = head.firstChild, wd; w && bdcol; w = w.nextSibling) {
				var wwd = cachedOffsetWidths[w.uuid]; //use the cached width

attached an example showing the effect grid-css-reflow-loop.zul

performance recording without width caching:

performance recording with width caching (saves 2.3 seconds in this trivial example, but also indicates the next problem area which might be addressed in a similar way):