Express.js使用express.Router处理用户注册返回500错误如何解决？

问题根因&修复方案 #

• 1. 中间件加载顺序错误（最核心问题）
     你在app.js中先注册了路由，之后才加载bodyParser中间件，导致post请求提交的表单数据无法被解析，req.body永远是空值，自然无法触发后续逻辑。只需要把bodyParser、fileUpload等请求解析中间件的加载逻辑，移到路由注册之前即可。
• 2. 异步逻辑执行顺序错误
     db.query和bcrypt.hash都是异步方法，你现在的写法是串行执行，会导致邮箱重复校验、密码校验还没出结果，就已经执行了插入数据库的逻辑，同时bcrypt.hash没有处理异步返回，存入数据库的是Promise对象而非加密后的密码字符串。需要把后续逻辑放到回调内，或者改用async/await写法简化逻辑。
• 3. 路由注册冗余错误
     你已经通过app.use('/', route)把路由挂载到了根路径下，后续的app.use('about', route)等写法不仅冗余，还缺少路径开头的斜杠，可能导致路由匹配异常，直接删掉即可。

修复后的代码 #

app.js

var express = require('express');
var handlebars = require('express-handlebars').create({ defaultLayout: 'main' });
var dotenv = require('dotenv');
var bodyParser = require('body-parser');

var fileUpload = require('express-fileupload');
var route = require('./routes/auth');
var app = express();

//diable metadata header response
app.disable('x-powered-by');

//app template configuration setup
app.engine('handlebars', handlebars.engine);
app.set('view engine', 'handlebars');

//static resources configuration
app.use(express.static(__dirname + '/public'));

// 【调整顺序：先加载请求解析中间件】
//file upload config
app.use(fileUpload());
app.use(express.static('upload'));

//form encoding
app.use(bodyParser.urlencoded({ extended: false }));

// 【后注册路由，删掉冗余的路由挂载】
app.use('/', route);

//app port for viewing
app.set('port', process.env.PORT || 3000);


//custom 404 page
app.use((req, res, next) => {
    res.status(404);
    res.render('404');
});

//custom 500 page
app.use((err, req, res, next) => {
    res.status(500);
    res.render('500');
});

app.listen(app.get('port'), (req, res) => {
    console.log('Express started on localhost:' +
        app.get('port') + '; press Ctrl-C to terminate.');
});

module.exports = app;

auth.js（用async/await简化异步逻辑，避免回调地狱）

var express = require('express');
var bcrypt = require('bcrypt');
var fortune = require('../lib/fortune');
var db = require('../controllers/database');
var router = express.Router();
// 把db.query封装成promise形式方便用await，如果你用的是mysql2模块本身就支持promise写法可以跳过这步
const util = require('util');
db.query = util.promisify(db.query);

// define the home page route
router.get('/', (req, res) => {
    res.render('home');
});


//About Page route
router.get('/about', (req, res) => {
    res.render('about', { fortune: fortune.getFortune });
});

//middleware registration page route
router.get('/register', (req, res) => {
    res.render('register');
});

// 加async关键字
router.post('/register',  async (req, res) => {
    try {
        var { firstName, lastName, email, password, passwordConfirm } = req.body;
        // 等待查询结果返回
        const results = await db.query('SELECT email FROM registration WHERE email = ?', [email]);
        if (results.length > 0) {
            return res.render('register', {
                message: 'That email is already in use'
            })
        } else if (password !== passwordConfirm) {
            return res.render('register', {
                message: 'Passwords do not match'
            })
        }
        // 等待密码加密完成
        let hashedPwd = await bcrypt.hash(password, 10);
        console.log(hashedPwd);
        // 等待插入完成
        await db.query('INSERT INTO registration SET ? ',  { firstName: firstName, lastName: lastName, email: email, password: hashedPwd });
        return res.render('register', {
            message: 'User registered'
        });
    } catch (error) {
        console.log(error);
        return res.status(500).render('register', {
            message: '系统异常，请稍后重试'
        })
    }
});


router.get('/login', (req, res) => {
    res.render('login');
});

module.exports = router;

内容的提问来源于stack exchange，提问作者GiddyGiddy