https://developers.google.com/web/fundamentals/instant-and-o...
IronDB redundantly stores data in multiple datastores -- cookies, IndexedDB, LocalStorage, and SessionStorage -- and self-heals if the data in any thereof is deleted or corrupted. For example, stored data is safeguarded in the event the user clears their cookies or IndexedDB is purged due to storage pressure.
tl;dr: IronDB is resilient in the face of data deletion. localForage isn't.
It would be nice to have an in-between where if a user authorized an app to permanently consume up to X amount of disk space the browser would allow it. But pulling off that user interaction well (i.e., getting the user to make an informed decision rather than blindly clicking yes or no) seems quite hard.