We maintain a similar Javascript library at work called jIO [1][2]. It provides the same API to different storages (currently Memory, IndexedDB, WebSql, WebDav, Dropbox, GoogleDrive, ERP5) plus handlers for functionality and complex storage trees (eg zip, union, query, replicate, crypt storage). It's relatively straightforward to extend and query data sources with an open API since you just have to reimplement the jIO API methods.
[1] https://jio.nexedi.com/ [2] https://github.com/nexedi/jio