Result: a, b, d, c. Expected: a, b, c, d

 const promises = []
    console.log('a')
    someFunc(promises)
    Promise.allSettled(promises).then(() => console.log('d'))

    function someFunc(promises) {
      const promise = new Promise(resolve => setTimeout(() => {
        console.log('b')
        const promise2 = new Promise(resolve2 => setTimeout(() => {
          console.log('c')
          resolve2()
        }, 3000))
        promises.push(promise2)
        resolve()
      }, 3000))
      promises.push(promise)
      return promise
    }

CodePudding user response：

While it'd be possible to patch it up by not pushing to an array, but instead having each Promise chain off of each other in someFunc...

console.log('a')
someFunc().then(() => console.log('d'))

function someFunc() {
  return new Promise(resolve => setTimeout(() => {
    console.log('b')
    new Promise(resolve2 => setTimeout(() => {
      console.log('c')
      resolve2()
    }, 3000))
      .then(resolve);
  }, 3000))
}

A much more understandable version would promisify setTimeout to begin with instead of doing it every time.

const setTimeoutPromise = ms => new Promise(resolve => setTimeout(resolve, ms));

console.log('a')
someFunc().then(() => console.log('d'))

function someFunc() {
  return setTimeoutPromise(3000)
    .then(() => {
      console.log('b');
      return setTimeoutPromise(3000)
    })
    .then(() => {
      console.log('c');
      return setTimeoutPromise(3000)
    });
}

Which can be further simplified with await...

const setTimeoutPromise = ms => new Promise(resolve => setTimeout(resolve, ms));

console.log('a')
someFunc().then(() => console.log('d'))

async function someFunc() {
  await setTimeoutPromise(3000);
  console.log('b');
  await setTimeoutPromise(3000);
  console.log('c');
  await setTimeoutPromise(3000);
}

CodePudding user response：

Solution

I know you may be confused on this question a lot. Here is the solution I found

const promises = []
const timeout = ms => {
    const promise = new Promise(resolve => setTimeout(resolve, ms))
    promises.push(promise)
    return promise
}

const someFunc = () =>
    timeout(1000).then(() => {
        console.log('b')
        timeout(1000).then(() => console.log('c'))
    })

async function main() {
    console.log('a')
    someFunc()
    let i = 0;
    while (promises.length > i) {
        i = promises.length
        await Promise.allSettled(promises)
    }
    console.log('d')
}

main()

The problem I really want to express is that the content of the function someFunc is not determined at compile time while I need to make sure that the function leave no side effect once executed.