Turning callbacks into async iterators, with a React hook-like API.

iterator.js

// Example usage:
//
// void async function() {
//   let [clicks, onclick] = iterator()
//   document.querySelector('button').addEventListener('click', onclick)
//   for await (let click of clicks) console.log(click)
// }()

export default function iterator() {
  let done = false
  let events = []
  let resolve
  let promise

  defer()

  return [read(), write, end]

  function defer() {
    promise = new Promise(r => resolve = r)
  }

  async function* read() {
    await promise
    yield* events.splice(0)
    if (!done) yield* read()
  }

  function write(event) {
    events.push(event)
    resolve()
    defer()
  }

  function end() {
    done = true
    resolve()
  }
}