Add a closed property on the db

[Jack-Works]

To reflect https://w3c.github.io/IndexedDB/#connection-closed

[jakearchibald]

+1 to this. Might be better as a .state that can express more than just a boolean, also a "statechange" event would be useful.

Right now, if a library takes a database to use, it has no way of knowing when or if the database has been closed. The "close" event only fires if the database was forcibly closed.

[evanstade]

@jakearchibald as far as the state, you can probably work around this by trying to create a transaction and catching the exception, if any. Is that being done today?

As for the close event, can you elaborate on the need for this change (to help set prioritization)?

[jakearchibald]

Hah it's been a few years. I think it was so a library could perform cleanup, because it knows the provided database is now closed.