Q:

Google App Script Debugger not working on ClickHandler callback

I've followed the Google app script tutorial here which is a very simple script with two functions. showDialog (which presents a dialog box with a text field and submit button ) and respondToSubmit(e) which handles the submit button and adds the entered data to the spreadsheet.
It works fine.
What doesn't seem to work is the debugger on the callback. So I place a breakpoint in both functons and start the showDialog function. The debugger kicks in and stops execution at the breakpoint. I click continue so I can interact with the newly opened dialog box. However when I click the submit button the debugger does not start again. The respondtoSubmit(e) function is executed. The debugger just does not stop on the breakpoint(s).
Is there a problem with debugging callbacks like this or can you only debug one function at a time?

A:

As of right now, the debugger has some unexpected behaviours.  Mostly, it seems to only respect breakpoints during calls from the script editor, so to debug your event handler you must call it from the debugger, not the UI.  If you need to peek into variables such as the event object passed to the function, for example, try adding this line to your handler where you'd normally put a breakpoint:
Logger.log(Utilities.jsonStringify(e));
Then view the log from the script editor after execution.

