I am trying to set window.onerror function to be able to create custom error page but something in Ext is blocking it. Do you have some explanation?
Based on that description, I would say your code is wrong.
You've been here for quite some time and should be familiar with posting a question with a reasonable amount of info, in order for anyone here to answer you.
Hey vlados, I don't have an answer to your question (since I can't see your code).
But, here's a extension I wrote that probably does what you need: