[TYPO3-dev] Simple way to enable BE JS debugging?

[Oliver Salzburg]

While trying to write my first BE module today, I pretty much instantly
ran into an issue while trying to implement a file browser in ExtJS.
I was looking at this article:
http://superdit.com/2011/06/01/extjs-simple-file-browser/

This results in:
ext-all-1ddb562089dfb84975963c2ce259146c.js:7 Uncaught TypeError:
undefined is not a function

So, that's not very helpful.
Obvious first step would be to switch to the debugging version of ExtJS.

How should that be done?
Is there some setting I can change that will cause the debug version to
be used automatically? Or do I have to replace the actual files?

Cheers
Oliver