joystream/storage-node/packages/util/externalPromise.js

/**
 * Creates a new promise.
 * @return { object} Returns an object that contains a Promise and exposes its handlers, ie. resolve and reject methods
 * so it can be fulfilled 'externally'. This is a bit of a hack, but most useful application is when
 * concurrent async operations are initiated that are all waiting on the same result value.
 */
function newExternallyControlledPromise() {
  let resolve, reject

  const promise = new Promise((res, rej) => {
    resolve = res
    reject = rej
  })

  return { resolve, reject, promise }
}

module.exports = {
  newExternallyControlledPromise,
}