我正在学习Mongoose从JavaScript无处不在的书，这是我必须写的代码：

const mongoose = require('mongoose');
const mongoose = require('mongoose');
module.exports = {
  connect: DB_HOST => {
    mongoose.connect(DB_HOST);
    mongoose.connection.on('error', err => {
      console.error(err);
      console.log('MongoDB connection error. Please make sure MongoDB is running.');
      process.exit();
    });
  },
  close: () => {
    mongoose.connection.close();
  }
}

当我把鼠标悬停在connect和connection上时，它会相应地显示Unresolved function or method connect()和Unresolved variable connection。我猜这本书是关于mongoose的旧版本，而在最新版本中它只是被删除了。它的新函数和变量是什么？