the IE specific *invoke *method on the Applet widget causes JS errors after code minification
(-> the error only happens when <debug-js> is enabled, e.g. in production while it works during development)

see: https://github.com/zkoss/zk/blob/v8.5.2.1/zul/src/archive/web/js/zul/med/Applet.js#L114-L120

The local variable 'n' becomes 'a' after minification leading JS to errors when evaluating 'expr' after an applet method is called using Applet.invoke().