Steps to Reproduce

https://zkfiddle.org/sample/3okm2g5/1-update-styles-performance
click anywhere on the screen

Current Result

it takes 4.3sec (with profiler enabled) to update the inline styles
most of the time is spent clearing the old styles (inefficiently)

Expected Result

evaluate whether this can be improved

Debug Information

https://github.com/zkoss/zk/blob/2c7ebc163661fd0e7f349da743190458ad089a07/zk/src/archive/web/js/zk/dom.ts#L1974-L1981

the inner loop is iterating over each possible CSS attribute (using for...in) mostly doing nothing

clearing the existing inline styles might be done as shown in the workraround

Workaround

removes the clearStyles overhead almost completely (however there might be a reason for the previous, more complex implementation)

zjq.prototype.clearStyles = function() {
   this.jq[0].style.cssText = null; 
   return this;
}