Promise.cancelable = pendingPromise => {
  let lazyCb = null;
  let settled = false;
  let canceled = false;

  const promise = Promise.resolve(pendingPromise).then(() => {
    settled = true;
    if (canceled) {
      return;
    }

    return lazyCb && pendingPromise.then(lazyCb);
  });

  return {
    then: cb => {
      if (canceled) {
        return;
      }

      if (settled) {
        promise.then(cb);
        return;
      }

      lazyCb = cb;
    },

    cancel: () => {
      if (!settled) {
        canceled = true;
      }
    },
  };
};