如何在ExpressJS中传递多路由设置中的DB对象？

// db.js

const mongoose = require('mongoose');

// 初始化数据库连接
mongoose.connect('mongodb://localhost/my_database', { useNewUrlParser: true, useUnifiedTopology: true });

// 创建DB对象
const db = mongoose.connection;

// 导出DB对象
module.exports = db;

// userRoutes.js

const express = require('express');
const db = require('./db'); // 引入db.js中导出的DB对象

const router = express.Router();

// 使用DB对象进行数据库操作
router.get('/users', (req, res) => {
  db.collection('users').find().toArray((err, users) => {
    if (err) throw err;
    res.json(users);
  });
});

module.exports = router;

// productRoutes.js

const express = require('express');
const db = require('./db'); // 引入db.js中导出的DB对象

const router = express.Router();

// 使用DB对象进行数据库操作
router.get('/products', (req, res) => {
  db.collection('products').find().toArray((err, products) => {
    if (err) throw err;
    res.json(products);
  });
});

module.exports = router;

// app.js

const express = require('express');
const userRoutes = require('./userRoutes');
const productRoutes = require('./productRoutes');

const app = express();

app.use('/api', userRoutes); // 挂载userRoutes到/api路径
app.use('/api', productRoutes); // 挂载productRoutes到/api路径

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});