I just published version 1.0.0 of billstclair/elm-port-funnel. It enables communicating with ALL of your custom JavaScript through a single Cmd/Sub port pair. It takes care of loading the JavaScript code, which you simply drop in a directory and add to a list, and dispatching messages from your Elm code. It allows pure-Elm simulators, to make testing your app easy in elm reactor.
https://package.elm-lang.org/packages/billstclair/elm-port-funnel/latest
The example is live at https://billstclair.github.io/elm-port-funnel
I will now begin work at converting my existing port modules to funnels. Those will be major version bumps, but will make them much easier to combine.
Thank you to @splodingsocks for the basic idea that I generalized to create this package.