generator异步

1. generator的使用

const fs = require('fs')

function * gen(data) {
  let a = yield data
  console.log(a)
  let b = yield a
  console.log(b)
}

let it = gen(123)

it.next() //第一个next传参没有意义
it.next(456) //把456传递给a
it.next(789) //把789传递给b

手写一个generator执行异步的函数

function genRun(fn) {
  let it = fn()

  function run(data) {
    const { value, done } = it.next(data)
    console.log(value, done)

    if (!done) {
      if (!!value && typeof value.then === 'function') {
        value.then(res => {
          run(res)
        })
      } else {
        run(value)
      }
    }
  }

  return run
}