app.js

// connect to mongo
require('./db').init(config.mongodb, function(err) {
	if (err) {
		throw err;
	} else {
		console.log('[app] connection to mongodb has been established');
		// Here you can start app, this will be after db connection init...
	}
});

db.js

'use strict';

var Client = require('mongodb').MongoClient,
	Collection = require('mongodbext').Collection,
	Steppy = require('twostep').Steppy,
	_ = require('underscore');

var exports = module.exports;

exports.init = function(config, callback) {
	Client.connect(config.url, function(err, db) {
		if (err) {
			callback(err);
			return;
		}

		var usersCol = exports.users = new Collection(db, 'users');
		usersCol.addPlugin('sequenceId');
		usersCol.addPlugin('createDate');
		usersCol.addPlugin('updateDate');
		// Here you can use beforeRemove, afterRemove, beforeUpdate e.t.c.
		usersCol.on('afterUpdate', function(params, callback) {
		  callback();
		});
    });
    
    callback();
});