What is the storage limit? Would be nice to offer some kind of helper function to return that. For instance, I want to store a base64 encoded image. I believe there is a 10MB limit imposed by Chrome on local storage (or something similar). Bypassing that restriction locally would be great. Could be a nice feature of ImmortalDB.
Also, if you are storing larger strings in local/sessionStorage, websql or indexdb, you should use lz-string[1] to try to minimize storage impact.
Aside: if you want something with a nicer interface for underlying storage you may want to look at pouchdb[2], which has a localized couch interface and supports remote synching to coudchdb, which is pretty nice.
[1] https://github.com/pieroxy/lz-string [2] https://pouchdb.com/