/**
 * @param { Promise } promise
 * @param { Object= } errorExt - Additional Information you can pass to the err object
 * @return { Promise }
 */
export function to<T, U = Error> (
  promise: Promise<T>,
  errorExt?: object
): Promise<[U, undefined] | [null, T]> {
  return promise
    .then<[null, T]>((data: T) => [null, data]) // 執(zhí)行成功，返回?cái)?shù)組第一項(xiàng)為 null。第二個(gè)是結(jié)果。
    .catch<[U, undefined]>((err: U) => {
      if (errorExt) {
        Object.assign(err, errorExt);
      }

      return [err, undefined]; // 執(zhí)行失敗，返回?cái)?shù)組第一項(xiàng)為錯(cuò)誤信息，第二項(xiàng)為 undefined
    });
}

export default to;

import to from 'await-to-js';
// If you use CommonJS (i.e NodeJS environment), it should be:
// const to = require('await-to-js').default;

async function asyncTaskWithCb(cb) {
     let err, user, savedTask, notification;

     [ err, user ] = await to(UserModel.findById(1));
     if(!user) return cb('No user found');

     [ err, savedTask ] = await to(TaskModel({userId: user.id, name: 'Demo Task'}));
     if(err) return cb('Error occurred while saving task');

    if(user.notificationsEnabled) {
       [ err ] = await to(NotificationService.sendNotification(user.id, 'Task Created'));
       if(err) return cb('Error while sending notification');
    }

    if(savedTask.assignedUser.id !== user.id) {
       [ err, notification ] = await to(NotificationService.sendNotification(savedTask.assignedUser.id, 'Task was created for you'));
       if(err) return cb('Error while sending notification');
    }

    cb(null, savedTask);
}