javascript traverse cancellable

traverseCancellable.js

/*
 * traverse cancellable takes an Array of promise's running them in parallel returning a single promise of their result and cancel function.
 *
 * @inputThunks Array[() => Promise[A]] an array of promises not yet started, thunks () => Promise
 * @returns Object {
 *   promise: Promise[Array[A]]
 *   cancel: Function() to cancel
 *  }
 */
export function traverseCancellable(inputThunks) {
  let running = true;

  function go(remaining, acc) {
    if (!running) {
      return Promise.reject('cancelled');
    } else if (remaining.length <= 0) {
      return acc;
    } else {
      const [head, ...tail] = remaining;
      return head().then(headResult => {
        return go(tail, [...acc, headResult]);
      });
    }
  }

  const promise = go(inputThunks, []);

  const self = {
    promise: promise,
    cancel: () => {
      running = false;
    },
    catch: (fn) => {
      promise.catch(fn);
      return self;
    }
  };
  return self;
}