Get number of history states via Photoshop Script

Question

I need to check the number of assigned history states for Photoshop, as part of a script's start-up, to verify that the user has enough undo states set for the script to function properly. I could simply set the number of states with the code I got from the ScriptListener plugin, but I know some users of my scripts use more history states than I would set myself, via this code; so I'd like to simply verify they have the minimum required number of history states before the script will run, or pop a warning or auto-adjust after confirmation if they do not.

So in short, I'm looking for a way to get the currently set number of History (undo) States, in Photoshop, via scripting. Also, if anyone also knows a way to set that number (without using ScriptListener code), I would be interested in that as well (and will up-vote the first working version of that answer).

Answer 1

If you need to know the number of History states in the active document just use this script

var history_number = app.activeDocument.historyStates.length;
alert(history_number );

But if you need the main number of history states in the photoshop preferences use this one

var Hsstnum = app.preferences.numberOfHistoryStates;
alert (Hsstnum);