跟着 blog 教程做, mongodb --auth, 连不上数据库

请教下该怎么做

教程源码

 var settings = require('../settings'),
 Db = require('mongodb').Db,
 Connection = require('mongodb').Connection,
 ObjectID = require('mongodb').ObjectID,
 Server = require('mongodb').Server;

    var db = new Db(settings.db, new Server(settings.host, Connection.DEFAULT_PORT, {}))


module.exports = db;