Promise.all proof by doing

output.log

Start | 1 | foo
Start | 2 | bar
Start | 3 | bazz
End | 2 | bar
End | 3 | bazz
End | 1 | foo
[ 'foo', 'bar', 'bazz' ]

promise-all.js

function waitAndLog({ num, str, timeout }) {
  return new Promise(function (resolve, reject) {
    console.log(`Start | ${num} | ${str}`);
    setTimeout(() => {
      console.log(`End | ${num} | ${str}`);
      resolve(str);
    }, timeout);
  });
}

var promise1 = waitAndLog({
  num: 1,
  str: 'foo',
  timeout: 1000
})
var promise2 = waitAndLog({
  num: 2,
  str: 'bar',
  timeout: 100
})
var promise3 = waitAndLog({
  num: 3,
  str: 'bazz',
  timeout: 500
})

Promise.all([promise1, promise2, promise3]).then(function(values) {
  console.log(values);
});
// expected output: Array [3, 42, "foo"]