localForage only uses a single datastore. E.g. LocalStorage or SessionStorage or IndexedDB. Thus, stored data is lost forever if the browser unceremoniously purges that datastore due to storage pressure.

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.