It seems like it's very easy in general to forget to add a transaction.onabort handler in code because aborts are so rarely seen. In particular, this has happened a few times in chrome privileged code where the lack of abort handling could potentially matter, so it would probably be useful to improve the ergonomics around this by logging something to the console and/or helping devtools expose a potential issue.

Analytically, because the abort event is bubbling one might also need to consider the state of the database, but arguably any asymmetric handling on the transaction or the database is probably a code smell.