Attaching custom data to sprite

Hi there.

Basiclally a simple thing, however i dont get an idea on how to solve this one:

Say I have a sprite which is already existing during runtime and at some certain point I want to attach some custom data to it, say, in a string.

How would I do that?

s:Sprite = new Sprite();
s[“extra”] = … gives me an error, so i got exactly that far till here.

s.name is already reserved for another string and for sure I thought about just adding a TextField with the string inside to it, like

s.addChild(myStringTf);

But I know there is a better way, I just cant find it.
hasOwnProperty() just returns a boolean true in case i match the value already assigned to it, right? Isn’t there a way to attach an annonymouse object to it? A little hint would be so apprecheated.

Best regards,
zoimt