I recently started looking into the most mature SQL database for the browser. My goal was similar, to be able take data as json or HTTP responses or csv or whatever and be able to pass them through a SQL engine with the user providing custom code/data the whole way.

Turns out the most mature JavaScript database is SQLite ported to webassembly: https://github.com/sql-js/sql.js.

Based on that research, I wrote a bit about running SQL and other languages entirely in the browser here: https://datastation.multiprocess.io/blog/2021-06-16-language...