I don't know anything about your game but I wonder if you could use SQLite to a similar effect. If you just want things as JS objects, you could have a Player

I don't know anything about your game but I wonder if you could use SQLite to a similar effect. If you just want things as JS objects, you could have a Player table with a column for playerID and a column for the JSON string. I'm not saying you shouldn't use Mongo/NoSQL, I just think SQLite is an interesting potential choice. (e.g. https://sqlite.org/appfileformat.html https://sqlite.org/appfileformat.html)