Can't tell if you mean overwriting after every keystroke (if so, no history); or saving a "fresh copy" after each keystroke (history, but terribly inefficient -

Can't tell if you mean overwriting after every keystroke (if so, no history); or saving a "fresh copy" after each keystroke (history, but terribly inefficient - localStorage has space limitations); or saving a series of diffs (how far do you have to go down that path before you realise you should have just used git?)