async-control-flow-with-promises.js

function map (arr, fn, ctx = this) {
  return Promise.all(arr.map((item, index) => {
    return new Promise((resolve, reject) => {
      fn.call(ctx, item, index, arr, resolve, reject)
    })
  }))
}

var arr = [1, 2, 3]

map(arr, (item, index, arr, resolve, reject) => {
  setTimeout(function () {
    resolve(item * 2)
  }, item * 500)
})
.then((values) => {
  console.log(values)
})