If you run into the issue
Warning: Unimplemented primitive used:put or whatever
put is for you, it's probably because you forgot to include the
[@bs.module "<library>"] or any other FFI before your wrapping.
external putJson: (string, Js.Json.t) => request = "put";
which gave me the error above ^. The fix?
[@bs.module "superagent"] external putJson: (string, Js.Json.t) => request = "put";
At least that was the case for me. (: