Creating an undo function

[Apexprim8]

Hello there.

I am looking for help from anyone who has designed an undo manager.

I have a manager that will save the current form object to a stack array. I fire this method on every controls GotFocus event.

However I am thinking - is there a way of only saving when the user has changed the form? Textchanged was an option I was thinking of but what if the user doesn't type any changes?

Any feedback thankfully received