Promise allSettled polyfill

all_settled.ts

type SettleResult<T> =
    | { status: 'fulfilled'; value: T }
    | { status: 'rejected'; reason: any };

function reflect<T>(promise: Promise<T>): Promise<SettleResult<T>> {
  return promise.then(
      value => ({ status: 'fulfilled', value }),
      reason => ({ status: 'rejected', reason }),
  )
}

function Promise_allSettled<T>(
    promises: readonly Promise<T>[],
): Promise<readonly SettleResult<T>[]> {
  return Promise.all(promises.map(reflect))
}

export const allSettled = 'allSettled' in Promise
    ? (Promise as any).allSettled as typeof Promise_allSettled
    : Promise_allSettled;