Node JS：promise 代替了 async/await

Question

我有种子文件

require('dotenv').config()

const db = require('./db');
const logger = require('./logger.js')
require('../models/adminModel')
var Admin = require('mongoose').model('Admins');

const seedAdmin = async () => {
  const new_admin = new Admin({email: "xyx@xyz.com", password: "admin@123"});
  await new_admin.save(function(err, task) {
    if (err)
      logger.error(`ERROR: ${err}`)
    logger.success(`Admin user created sucessfully with email: ${new_admin.email}`)
  });

  return 'resolved'
}

async function asyncCall() {
  console.log('calling');
  var result = await seedAdmin();
  console.log(result);
  process.exit();
}

asyncCall();

这段代码的输出是

calling
resolved

我研究后写了这段代码

require('dotenv').config()

const db = require('./db');
const logger = require('./logger.js')
require('../models/adminModel')
var Admin = require('mongoose').model('Admins');


function seedAdmin() {
  return new Promise(resolve => {
    const new_admin = new Admin({email: "xyx@xyz.com", password: "admin@123"});
    new_admin.save(function(err, result) {
      if (err)
        logger.error(`ERROR: ${err}`)
        resolve('resolved');
      logger.success(`Admin user created sucessfully with email: ${new_admin.email}`)
      resolve('resolved');
    });
  });
}

async function asyncCall() {
  console.log('calling');
  var result = await seedAdmin();
  console.log(result);
  process.exit();
}

asyncCall();

输出正确

calling
✔  success   Admin user created sucessfully with email: xyx@xyz.com
resolved

根据此声明，第一个代码应该可以工作 异步函数返回一个承诺。反之亦然。每个返回 promise 的函数都可以被认为是异步函数

我无法理解它缺少什么，我是 Nodejs 的新手 帮助将不胜感激

Answer 1

您没有为new_admin.save() 接口提供文档，但在99% 的情况下，当接口同时支持promise 和旧的回调样式时，如果您传递回调，那么它将不会返回promise。

所以，当你这样做时：

  await new_admin.save(function(err, task) {
    if (err)
      logger.error(`ERROR: ${err}`)
    logger.success(`Admin user created sucessfully with email: ${new_admin.email}`)
  });

您将回调传递给admin.save()，因此它不会返回承诺。所以，await 没有任何用处。它不会等待异步操作完成。 await 仅当它等待的值是一个承诺时才会做一些有用的事情。

相反，不要混合使用普通的回调和承诺。完全使用 Promise。

const seedAdmin = async () => {
  const new_admin = new Admin({email: "xyx@xyz.com", password: "admin@123"});
  try {
      let result = await new_admin.save();
      logger.success(`Admin user created sucessfully with email: ${new_admin.email}`)
      return 'resolved';
  } catch(err) {
      // log and rethrow so caller still sees error
      logger.error(`ERROR: ${err}`)
      throw err;
  }
}

或者，不使用 `await'，您可以这样做：

const seedAdmin = () => {
    const new_admin = new Admin({email: "xyx@xyz.com", password: "admin@123"});
    return new_admin.save().then(result => {
      logger.success(`Admin user created sucessfully with email: ${new_admin.email}`)
      return 'resolved';
    }).catch(err => {
       // log and rethrow so caller still sees error
       logger.error(`ERROR: ${err}`)
       throw err;        
    });
};