Postgress has build-in v8 javascript functions to manage this ( as stated before). Which makes it much more useable.
There's a good library for .net that handles postgress documents, which has an insane amount of usefull functions ( https://martendb.io/documentation/documents/ ). I think halve of those wouldn't be possible on another database.
You don't really need v8 JavaScript functions built-in in the database when you use SQLite, because SQLite is running in the same process than your application. The round trips between your application and SQLite cost almost nothing.
The main reason why main client-server databases have so many built-in functions is because of the round-trips. Let's say you want to filter rows based on the result of some function, if your function is implemented client-side, then the database would have to send each row to the client.