promise-with-resolvers.ts

/**
 * This module implements ECMAScript (stage-3) proposal:
 * Promise with resolvers:
 * https://github.com/tc39/proposal-promise-with-resolvers
 *
 * Copyright 2023 Slava Fomin II
 *
 * Permission is hereby granted, free of charge, to any
 * person obtaining a copy of this software and associated
 * documentation files (the “Software”), to deal in the
 * Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice
 * shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF
 * ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

export interface PromiseWithResolvers<Type = unknown> {
  promise: Promise<Type>;
  resolve: ResolveFunc<Type>;
  reject: RejectFunc;
}

export type ResolveFunc<Type = unknown> = (
  (value: (Type | PromiseLike<Type>)) => void
);

export type RejectFunc = (
  (reason?: any) => void
);


export function promiseWithResolvers<
  Type = unknown

>(): PromiseWithResolvers<Type> {

  let resolve: (ResolveFunc<Type> | undefined);
  let reject: (RejectFunc | undefined);

  const promise = new Promise<Type>(
    ($resolve, $reject) => {
      resolve = $resolve;
      reject = $reject;
    }
  );

  // Type safety
  if (!resolve || !reject) {
    throw new ReferenceError();
  }

  return {
    promise,
    resolve,
    reject,
  };

}