将setTimeout的轮询包裹成Promise

wrap-setTimeoutLoop-to-promise.js

const cache = {
  resolve: null
}

let timerId

function finish(b) {
  console.warn('---------finish-------')
  if (cache.resolve) {
    console.warn('---------cache.resolve-------', b)
    cache.resolve(b)
  }
  delete cache.resolve
  delete cache.reject
}

async function startPoll() {
  const a = Math.random()
  console.warn('execute once', a)
  if (a > 0.93) {
    stopPoll(`stop by ${a}`)
  } else if (a > 0.2) {
    timerId = setTimeout(() => startPoll(), 111)
  } else {
    finish(a)
  }
}

function stopPoll(err) {
  clearTimeout(timerId)
  cache.reject && cache.reject(err)
  delete cache.resolve
  delete cache.reject
}

function main() {
  stopPoll()
  timerId = setTimeout(() => startPoll(), 111)
  const currentProcess = new Promise((r, j) => {
    if (cache.resolve) {
      cache.resolve(currentProcess) // 接续上一个promise
    }

    cache.resolve = function(...x) {
      r(...x)
    }

    cache.reject = function(...x) {
      j(...x)
    }
  })
  return currentProcess
}

main()
  .then(raw => console.warn('main result:', raw))
  .catch(console.warn)