How to connect to MongoDB from Node.js

nodejs-meet-mongo.js

var mongodb = require('mongodb');

var server = new mongodb.Server('hostname', portnumber, {auto_reconnect: true});
var db = new mongodb.Db('databasename', server);

db.open(function (err, db) {
	if (err) {
		console.error(err);
	} else {
		db.authenticate('username', 'password', function(){
			// ready for you, sir.
		});
	}
});

can you give sample code to connect with connection string