execute.ts

import {AbortError} from './AbortError';

/**
 * Similar to `new Promise(executor)`, but allows executor to return abort
 * callback that is called once `signal` is aborted.
 *
 * Returned promise rejects with `AbortError` once `signal` is aborted.
 *
 * Callback can return a promise, e.g. for doing any async cleanup. In this
 * case, the promise returned from `execute` rejects with `AbortError` after
 * that promise fulfills.
 */
export function execute<T>(
  signal: AbortSignal,
  executor: (
    resolve: (value: T) => void,
    reject: (reason?: any) => void,
  ) => () => void | PromiseLike<void>,
): Promise<T> {
  return new Promise<T>((resolve, reject) => {
    if (signal.aborted) {
      reject(new AbortError());
      return;
    }

    let removeAbortListener: (() => void) | undefined;
    let finished = false;

    function finish() {
      if (!finished) {
        finished = true;
        if (removeAbortListener != null) {
          removeAbortListener();
        }
      }
    }

    const callback = executor(
      value => {
        resolve(value);
        finish();
      },
      reason => {
        reject(reason);
        finish();
      },
    );

    if (!finished) {
      const listener = () => {
        const callbackResult = callback();

        if (callbackResult == null) {
          reject(new AbortError());
        } else {
          callbackResult.then(
            () => {
              reject(new AbortError());
            },
            reason => {
              reject(reason);
            },
          );
        }

        finish();
      };

      signal.addEventListener('abort', listener);

      removeAbortListener = () => {
        signal.removeEventListener('abort', listener);
      };
    }
  });
}