Since PRPC 6.3SP1 there is a OTB activity that can be used to toggle JS Compacting on and off. We asked for this so we didn't have to add the activity at client sites to disable the compacting. Also, the user you are working with does not need to have access to the developer portal to run the activity.
The activity updates the current operators record and sets the "pyPreferences.pyGeneralPrefs.pyDisableJSCompacting" accordingly. You have to start a new session to see the JS compacting differences. (Same as the above example provided by Susan)
Once you are done debugging make sure you run the activity again with a Compact=true parameter to get the user you are testing with back to a normal state.