@virtualstate/union/src/is-promise.ts

Concurrent union

export function isPromise<T = unknown>(value: unknown): value is Promise<T> {
  function isPromiseLike(value: unknown): value is { then?: unknown } {
    return typeof value === "object";
  }
  return (
    isPromiseLike(value) &&
    value.then instanceof Function
  );
}