Need to get the value before the transaction

Hi, is there a way to get the value before and after the transaction?
For example if I have a Y.Map { ‘my-key’ : ‘my_val’ } and after transaction it becomes
{ ‘my-key’ : ‘new_val’ }, how can I know what previous value was there (in the example it’s my_val) given then I am hooked to on(‘update’ … ) event

There are beforeTransaction and afterTransaction events on the Doc:

Also the observe event on the Y.Map contains the old value in ymapEvent.changes.keys.get(key).oldValue: