For reference I also found these older topics that talk about JS based addons.
and
Your linked topic seems to be talking about giving Card javascript access to an API which they can use to directly interact with Anki.
e.g. to find out how many cards are left to review, or allow editing in-reviewer.
It seems to me that dae’s biggest objection to that is that it makes previously “safe” shared decks become inherantly dangerous by giving them deeper access to your system.
This is not what I am proposing here.
My proposal is just a way to make the existing kind of addons we have work in a different way that has some benefits over what the current Python addons offer.
e.g. you could have something like FSRS Helper that can be used on AnkiMobile/AnkiDroid.
To me this seems like it should be much less objectionable, and should in fact make things safer because of the sandboxing.
There would be nothing stopping you from later creating some kind of mechanism for letting Decks “recommend” Addons or letting Cards talk to Anki/Addons, but that is not the main point of this proposal.