javascript - 在 promise 中包装异步函数

Question

我正在创建一个简单的 Web 应用程序，该应用程序使用 Express 和 Sequelize 处理请求并与 SQL 数据库通信。目前我在对象上调用异步函数时遇到问题，this对象的一部分是 undefined .我将函数包装在 express-async-handler 中处理 promise 返回，奇怪的是，如果我删除异步方法上的处理程序包装器，我就可以访问 this但正如预期的那样没有正确处理错误。我误解/做错了什么？下面是代码:
用户 Controller .js

var models  = require('../models');
const asyncHandler = require('express-async-handler')

var user = models.User

exports.registerUser = asyncHandler(async function(req, res) {
  var username = req.body.username,
      password = req.body.password;
      u = user.build({
        username: username, password: password
      })
  
      await u.registerUser()
      res.send('hello world')
  }
);

user.js 不工作

const bcrypt = require('bcrypt');
const asyncHandler = require('express-async-handler')

module.exports = (sequelize, DataTypes) => {
  const User = sequelize.define('User', {
    id: {
      type: DataTypes.UUID,
      defaultValue: sequelize.literal('uuid_generate_v4()'),
      primaryKey: true
    },
    name: DataTypes.STRING,
    username: DataTypes.STRING,
    password: DataTypes.STRING,
  }, {
    paranoid: true,
  });

  // Associations
  User.associate = function(models) {
    // associations can be defined here
    User.hasMany(models.Cat, {
      foreignKey: 'userId',
      as: 'cats',
      onDelete: 'CASCADE',
    })
  };

  // Instance methods
  User.prototype.registerUser = asyncHandler(async function () {
    await bcrypt.hash(this.password, 10, (err, hash) => {  // not able to access 'this'
      if(err) throw err;

      // Set the hashed password and save the model
      this.password = hash;
      this.save()
    });
  })
};

user.js 删除 asyncHandler() 工作

const bcrypt = require('bcrypt');
const asyncHandler = require('express-async-handler')

module.exports = (sequelize, DataTypes) => {
  const User = sequelize.define('User', {
    id: {
      type: DataTypes.UUID,
      defaultValue: sequelize.literal('uuid_generate_v4()'),
      primaryKey: true
    },
    name: DataTypes.STRING,
    username: DataTypes.STRING,
    password: DataTypes.STRING,
  }, {
    paranoid: true,
  });

  // Associations
  User.associate = function(models) {
    // associations can be defined here
    User.hasMany(models.Cat, {
      foreignKey: 'userId',
      as: 'cats',
      onDelete: 'CASCADE',
    })
  };

  // Instance methods
  User.prototype.registerUser = async function () {
    await bcrypt.hash(this.password, 10, (err, hash) => {
      if(err) throw err;

      // Set the hashed password and save the model
      this.password = hash;
      this.save()
    });
  }
};

Answer 1

I am wrapping the functions in the express-async-handler to handle the promises returns

不，你不需要这样做。您的 promise 返回 User.prototype.registerUser方法处理得很好

await u.registerUser()

您只需要 asyncHandler Express 路由处理程序的包装器，它不知道如何处理 async function 返回的 promise s。

If I remove the handler wrapper on the async method I am able to access this, but as expected does not handle errors correctly.

asyncHandler也无助于处理该错误。问题是你做

if(err) throw err;

在异步回调中，这只是使您的应用程序崩溃的未处理异常。相反，您需要 promisify bcrypt.hash这样你就会得到一个会被拒绝的 promise 。或者只是 use the promise version :

User.prototype.registerUser = async function () {
  const hash = await bcrypt.hash(this.password, 10)
  this.password = hash;
  await this.save()
};