billstclair/elm-port-funnel allows you to use a single outgoing/incoming pair of ports to communicate with the JavaScript for any number of PortFunnel-aware modules, which I'm going to call "funnels".
On the JavaScript side, you pick a directory for PortFunnel.js and the JavaScript files for the funnels. Some boilerplate JS in your index.html file loads PortFunnel.js, and tells it the names of the funnels. It takes care of loading them and wiring them up.
On the Elm side, you create the two ports, tell the PortFunnel module about them with a Config instance, call the action functions in the funnel modules, in response to events, and dispatch off of the name field in the GenericMessage you get from your subscription port, to process that message in each specific module, and handle its result. This is illustrated in example/Main.elm.
DEVELOPERS-GUIDE.md has details for people who want to write funnels. For simple examples, see the files Echo.elm and AddXY.elm in the src/PortFunnel directory, and the corresponding Echo.js and AddXY.js files in the example/site/js/PortFunnel directory.
The README in the example directory tells you how to configure the JavaScript for your own funnels. The example is live at billstclair.github.io/elm-port-funnel.
Currently, the PortFunnel.Echo and PortFunnel.AddXY modules, which ship with billstclair/elm-port-funnel, are the only funnel modules. I'll be working on upgrading my existing port packages to funnels (billstclair/elm-websocket-client, billstclair/elm-localstorage, billstclair/elm-dev-random).
Thank you to Murphy Randall (@splodingsocks on Twitter and Elm Slack), whose elm-conf 2017 talk introduced me to the idea that billstclair/elm-port-funnel takes to its logical extreme.