you can find methods by exploring the steem object of steemjs, all reads are in api, all writes in broadcast.

To see the arguments passed to the blockchain, the best doc is this at the moment: https://steemit.github.io/steemit-docs/

The best way to do it in my opinion if you want to go in depth is to read the blockchain source source here: https://github.com/steemit/steem/blob/27b7bdf04c3d195b97328bb20c27d659dc8ae31d/libraries/app/database_api.cpp#L1491