Comment by CapsAdmin

I find that these complex types often reflect the underlying complex code. This usually happens when you interact with something that is explicitly written for javascript and takes advantage of its dynamic nature. (usually the base javascript api)

window.addEventListener(event, callback), dispatchEvent(event) and removeEventListener(callback) is a good example. In a dynamic language, this api is at least unsurprising. It's easy to understand.

In a typed language, although strategies could vary, one would probably not write the api like that if you prefer to have simpler types.

Something like this would make more sense in a typed language:

import { onChange } from 'events'

const event = onChange.Add((event) => {

})

event.Remove()

// ..

event.onChange.Dispatch({value: "1,2,3"})