I'm no Elm expert, but as far as I understand, the "native library" APIs, the kind that are used to actually wrap browser APIs and interface with javascript in

I'm no Elm expert, but as far as I understand, the "native library" APIs, the kind that are used to actually wrap browser APIs and interface with javascript in a way that can be published and made reusable, is "private". I mean, you can look at the source and make your own, but you're playing in undocumented, unstable territory. The only "official" interop channel is the "port" system, which only lets you do a publisher/subscriber type thing with your application at runtime, and cannot be used in a library. So you basically cannot make a "blessed" library that uses native browser APIs.