Implement a configurable error logging and avoid empty catch statements such as here:
e.g.
https://github.com/zkoss/zk/blob/48504eabb498d0b87b8037a1a4cce9747d1ee4f0/zul/src/archive/web/js/zul/wgt/Popup.js#L269

At least if <debug-js> is enabled errors should be logged to the browser console, in order to identify problem sources.