> save all values everywhere: why not select the one that would last the longest (that people delete least often)?

For improved resiliency.

You can also configure IronDB to only use any two datastores of your choice, if you so desire: IronStorage's constructor takes an Array of storage implementations of your choice. See https://github.com/gruns/irondb#api.

> So you delete data when the user wants to delete data. Which database doesn't have this feature?

A database where the data therein can be deleted without warning. Browsers unceremoniously delete IndexedDB, LocalStorage, and SessionStorage under storage pressure. See https://developers.google.com/web/fundamentals/instant-and-o...

> doesn't use Flash, Silverlight, or Java -- which do?

Evercookie, a similar library, uses Flash, Silverlight, and/or Java.

See https://github.com/samyk/evercookie.

> No offence to the author but all this sound malicious. Perhaps this is why evercookie isn't maintained?

No offense taken.

Thank you for your feedback, kreetx. Don't hesitate to let me know if I can answer any other questions, or if there's anything else I can do for you.