API to simulate the "close" event

[nolanlawson]

The "close" event on an IDBDatabase only fires when the database closes for an abnormal reason, as described in the spec. (An abnormal reason would be something like the user clearing their browser data while the IDB connection is open.)

For unit testing, it would be neat if fakeIndexedDB had an API for simulating this abnormal close event. Presumably it would just be a matter of running db.close() plus firing an event. (I would do this in userland, but it seems that fakeIndexedDB throws an error if you try to call db.dispatchEvent(new CustomEvent('close')).

[bugeats]

According to the MDN spec, it also needs to support addEventListener like so:

db.addEventListener("close", () => {
  console.log("Database connection closed");
});

And yeah @nolanlawson I ran into this when trying to do the perfectly reasonable task of writing tests to handle the DB closing when asking for a new transaction.