[Question] What kind of role do `unit` that in `scheduler` play?

[Cong-Cong Pan]

The following code may be the same. I'm not sure.

Origin:

export const schedule = (cb) => unit.push(cb) === 1 && postMessage()

const postMessage = (() => {
  const cb = () => unit.splice(0, unit.length).forEach((c) => c())
  if (typeof MessageChannel !== 'undefined') {
    const { port1, port2 } = new MessageChannel()
    port1.onmessage = cb
    return () => port2.postMessage(null)
  }
  return () => setTimeout(cb)
})()

After:

export const schedule = cb => {
  if (typeof MessageChannel !== 'undefined') {
    const { port1, port2 } = new MessageChannel()
    port1.onmessage = cb
    port2.postMessage(null)
  } else {
    setTimeout(cb)
  }
}

[伊撒尔]

因为有时候在执行 flushwork 的同时，会push进来 effects，为了保证 effects 在当前组件的 flushwork 后执行，所以使用了一个小队列，也就是 unit

[Cong-Cong Pan]

啊哈，明白了！微任务之前有可能 push 进其他任务。