promise_serial.js

/**
 * Take an iterable of Promises and invoke them serially, otherwise identical
 * to the `Promise.all` static method.
 *
 * @param {Promise[]} promises
 * @return {Promise}
 */
function serial (promises) {
  const results = []

  return (Array.isArray(promises) ?
    promises : Array.from(promises))
  .reduce((chain, promise, index) =>
    chain.then(result => {
      if (index) results.push(result)
      return promise
    }), Promise.resolve())
  .then(result => {
    if (promises.length) results.push(result)
    return results
  })
}