promise.all.each.js

let arr = [1, 2, 3], res = [];

function later(i) {
  console.log('sched:', i)
  return new Promise((res, rej) => {
    setTimeout(() => {
      console.log('resolve:', i)
      res(i)
    }, 1000*i)
  })
}

function all() {
  return Promise.all(arr.reduce((acc, curr) => {
    acc.push(later(curr).then(i => res.push(i)))
    return acc
  }, []))
}

//all()

function each() {
  return arr.reduce((acc, curr) => {
    return acc.then(i => later(curr).then(i => res.push(i)))
  }, Promise.resolve())
}

//each()

async function asyncEach() {
  for(let curr of arr) {
    let i = await later(curr)
    res.push(i)
  }
}

//asyncEach()