How to simply delay Promises generated from array executed in Promise.all.

asyncDelay.js

const time = Date.now();
const data = ["a", "b", "c", "d"];

// this is actually what I want
const delay = (cb, timeout) =>
  new Promise(resolve => setTimeout(() => resolve(cb()), timeout));

// this simulates async call network/io operation
const fakeAsync = log =>
  new Promise(resolve => {
    console.log(`started ${log}`, Date.now() - time);
    setTimeout(() => {
      console.log(`ended   ${log}`, Date.now() - time);
      return resolve(log);
    }, Math.floor(Math.random() * 1000));
  });

console.log("preparation", Date.now() - time);
// and this is how to execute
const promises = data.map((d, index) => delay(() => fakeAsync(d), 100 * index));

console.log("started all", Date.now() - time);
Promise.all(promises).then(console.log);