_track-thenable-state.ts

export type Thenable<T> = PendingThenable<T> | FulfilledThenable<T> | RejectedThenable<T>

export type PendingThenable<T> = Promise<T> & { status: 'pending' }
export type FulfilledThenable<T> = Promise<T> & { status: 'fulfilled', value: T }
export type RejectedThenable<T> = Promise<T> & { status: 'rejected', reason: unknown }


export function trackThenableState<T>(promise: Promise<T>): Thenable<T> {
  const thenable = promise as Thenable<T>;
  if ("status" in thenable && typeof thenable.status === "string") {
    return thenable;
  }
  thenable.status = "pending";
  thenable.then(
    (value) => {
      const fulfilledThenable = thenable as FulfilledThenable<T>;
      fulfilledThenable.status = "fulfilled";
      fulfilledThenable.value = value;
    },
    (error) => {
      const rejectedThenable = thenable as RejectedThenable<T>;
      rejectedThenable.status = "rejected";
      rejectedThenable.reason = error;
    }
  );
  return thenable;
}

track-thenable-state.js

/**
 * @template T
 * @typedef {PendingThenable<T> | FulfilledThenable<T> | RejectedThenable<T>} Thenable<T>
 */

/**
 * @template T
 * @typedef {Promise<T> & { status: 'pending' }} PendingThenable<T>
 */

/**
 * @template T
 * @typedef {Promise<T> & { status: 'fulfilled', value: T }} FulfilledThenable<T>
 */

/**
 * @template T
 * @typedef {Promise<T> & { status: 'rejected', reason: unknown }} RejectedThenable<T>
 */

/**
 * @template T
 * @returns {Thenable<T>}
 */
export function trackThenableState(/** @type {Promise<T>} */ promise) {
  const thenable = /** @type {Thenable<T>} */ (promise);
  if ('status' in thenable && typeof thenable.status === 'string') {
    return thenable;
  }
  thenable.status = 'pending';
  thenable.then(
    (value) => {
      const fulfilledThenable = /** @type {FulfilledThenable<T>} */ (thenable);
      fulfilledThenable.status = 'fulfilled';
      fulfilledThenable.value = value;
    },
    (error) => {
      const rejectedThenable = /** @type {RejectedThenable<T>} */ (thenable);
      rejectedThenable.status = 'rejected';
      rejectedThenable.reason = error;
    }
  );
  return thenable;
}