How to detect Debug mode in JavaScript

I’ve asked a question on forum:

AJAX ScriptManager Class  has a IsDebuggingEnabled property, that is available in server code. I want in my client Javascript function to determine, do I running debug or release mode.

MS Online Community Support suggested :

You can create a hidden field to the page, then, check the IsDebuggingEnabled property of ScriptManager , if it is true, set the value of the hidden field to “true”, else, false.

It will work, but I expected the method available in some AJAX client library class.