Not a database, just a map of json strings where you can update the json stored at some key. You could write the same interface on top of localStorage.
Literally did something similar just last week, was looking for a good redis gui on windows and couldn't find one that clicked (closest I got was Another Redis Desktop Manager but it sorted my keys like 1, 11, 2 etc) so turned to sqlite and implemented this. Also added a "sync to disk" method so I get both the benefits of ram and persistence, worked out great since the data I'm getting over tcp has a sequence number so in case of any errors I resume from the last sequence number in the db. Thinking of fully committing and moving some stuff from the language like decoding the raw bytes to build a json object to an extension.
What's it give you above just holding a big object in memory? I guess partial serialization is something, so updates are stored on disk... But then why not just store a json file per key on disk? It's not like the serialized blobs allow you to have indexes or a particularly efficient full text search, so why bother with the SQL statements at all?