TS implementation of a promise that can be resolved after it has been created.

create-resolvable-promise.ts

type Resolver<T> = (value: T | PromiseLike<T>) => void;
type Rejector = (reason?: any) => void;
type ResolvablePromise<T> = Promise<T> & { resolve: Resolver<T>, reject: Rejector }
export function createResolvablePromise<T>(): ResolvablePromise<T> {
  let res: Resolver<T>
  let rej: Rejector;
  const promise = new Promise((r, s) => (res = r, rej = s)) as ResolvablePromise<T>;
  promise.resolve = res;
  promise.reject = rej;
  return promise;
}