(This is just a quick write-up since the question/ topic came up on the Deno Fresh discussion board (“State sharing between islands”) to which I wrote a short reply. I felt like elaborating here. The examples are stripped to bare minimum, so there’ll be no TS definitions and no import maps.) Let’s say you’ve built a new site using the wonderful Deno Fresh web framework. You have a number of unconnected islands all over the place and now want them to interact with eachother without resorting to hacks like passing data around using some key on the window object.