I tried an older version of ext-js 4 and the error is gone, but still nothing happens (complete white page). Then I deleted the whole directory of ext-js again and copied the content of 4.0.2a again, and the error is still gone.
So I have no idea why this error is not there anymore.
Same result in IE and Firefox.
Unfortunately, I think the only way to get past this is to see where in the call stack this is, and what it's trying to create?
via call stack, it is trying to invoke constructor method of my self-defined class which extends Ext.tree.Panel or Ext.panel.Panel. which I don't understand is why there is no constructor? I didn't override constructor in my self-defined class so that I expected Extjs would call the parent's constructor instead.
ok - so if it's trying to construct your extension, and the constructor doesn't exist, then that implies that Ext.define didn't work. The most likely reason (other than straight JS error), would be that the class you're extending is not loaded.
so, at the point of failure, can you go to the console and enter Ext.tree.Panel and then Ext.panel.Panel, and see if they're defined?
If they are, I'd look to see if you're having some sort of silent failure in Ext.define.
@hauke - I think you purged the elves from your configuration