having $output be a function. But give it properties also

It's hacky, but I do that like this:

$output = [getPlugin()]

getPlugin() =>
  if(!window.__fooPluginFn) {
    function foo(a, b, c) {
      // the actual plugin code
    }
    foo.prop = "blah";
    foo.anotherProp = 123;
    window.__fooPluginFn = foo;
  }
  return window.__fooPluginFn;

I have thought about something like $onLoad before, but there were some complications. Currently the lists panel is purely "declarative" (loosely speaking, in the sense that no state is altered during parsing/init) and all actual execution is done via calls from the HTML panel. It's definitely possible to have something like $onLoad but it does lead to a few extra "if/thens" that devs need to keep in their mind when importing something, and I'd need to change some ~deep-ish engine code. When I've had this need in the past I also noticed that I sometimes wanted it to only run if it was a direct import - i.e. not an import of an import. So there are a few DX questions there too. For now I think this one is further down the todo/to-think-about list, since it's pretty easy to just add [yourPlugin({init:true})] to the top of the HTML panel.