all-settled.js

/**
 * Returns a promise that is fulfilled with an array of promise state
 * snapshots, but only after all the original promises have settled, i.e.
 * become either fulfilled or rejected.
 *
 * See https://github.com/kriskowal/q/wiki/API-Reference#promiseallsettled
 */
allSettled = (promises) => {
  let resolve, outer = new Promise((r) => { resolve = r })
  let snapshots = [], settledCount = 0
  let handler = (index, state, value) => {
    snapshots[index] = {
      state,
      [state === 'fullfiled' ? 'value' : 'reason']: value
    }
    // Resolve the outer promise if all the original promises have settled.
    promises.length === ++settledCount && resolve(snapshots)
  }

  promises.forEach(function (promise, index) {
    promise.then(
      handler.bind(null, index, 'fullfiled'),
      handler.bind(null, index, 'rejected')
    )
  })

  return outer
}

allSettled([Promise.resolve('foo'), Promise.reject('bar')])
  .then((snapshots) => {
    console.log.apply(console, snapshots)
  })
// Object {state: "fullfiled", value: "foo"} Object {state: "rejected", reason: "bar"}