I got the following message from backbone-indexeddb sometimes: Couldn't not connect to the database (seems like that library needs to fix its double negative). Digging in a bit more, e.srcElement.error.message has this: The requested version (6) is less than the existing version (7). It's a VersionError (seems to be an official IndexedDB thing).

This might be a niche development problem. It came as I was doing some git reset --hard to git bisect a problem with tags. It seems that the schema in app/scripts/migrations/note.js goes up to version 6 in the current version but I must have grabbed a higher version later.

I was able to get it working again (I think) by manually deleting the database: first listed dbs per this and then ran indexedDB.deleteDatabase('notes-db'); from the console. But maybe the application could fixed to recover from these types of errors on its own.