Yes the answer is always ports when this topic comes up. Unfortunately one can only pass some basic types through ports. Passing a RegExp or an Intl.DateTimeFormat is not possible. It needs a wrapper on the Elm side, and the Elm people decided I can't be trusted to write this wrapper for me.

Back then if I wanted to search a list of strings for entries that match a regex supplied at run-time, I'd have to pass the whole list through a port, filter it outside, then pass it back in. Rather than just using the filter function. Ports are asynchronous messaging which means I have to restructure the whole code and wait for a state change when the filtered list is returned.

Let me cite the Elm docs on ports[1]: "Definitely do not try to make a port for every JS function you need."

So! Where does that leave me? Unsupported, that's where. Because I need a JS function. In 0.18 unsupported was fine. They broke it for 0.19 and the project died. Maybe it was dying of other causes anyway, but that one action sure drove people away.

[1] https://guide.elm-lang.org/interop/ports