Async&await原理分析.md

Async&await原理分析

function fn(nums) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(nums * 2)
    }, 1000)
  })
}
function* gen() {
  const num1 = yield fn(1)
  const num2 = yield fn(num1)
  const num3 = yield fn(num2)
  return num3
}
function generatorToAsync(generatorFn) {
  return function () {
    return new Promise((resolve, reject) => {
      const g = generatorFn()
      const next1 = g.next()
      next1.value.then(res1 => {

        const next2 = g.next(res1) // 传入上次的res1
        next2.value.then(res2 => {

          const next3 = g.next(res2) // 传入上次的res2
          next3.value.then(res3 => {

            // 传入上次的res3
            resolve(g.next(res3).value)
          })
        })
      })
    })
  }
}

const asyncFn = generatorToAsync(gen)

asyncFn().then(res => console.log(res)) // 3秒后输出 8