module-init-pattern-with-promises.js

// in app.js

var _ = require('lodash');
var Promise = require('bluebird');

// A global context object for accessing the other modules
var modules = {};

// Would be loaded from a server-specific file, each module has some options in its own property sometimes
var options = {};

var model = loadModule('model');
var express = loadModule('express');
var routes = loadModule('routes');

model.init()
  .then(express.init())
  .then(routes.init())
  .then(function() {
    console.log('Ready and listening');
  }).catch(function() {
    console.error('bad news, everyone!');
  });

function loadModule(name) {
  context[name] = require('./lib/' + name)(context, options[name] || {});
  return context[name];
}

// in model.js

var Promise = require('bluebird');
var mongodb = require('mongodb');

module.exports = function(context, options) {
  var self = {};
  self.context = context;
  self.options = options;
  self.init = function() {
    return mongodb.MongoClient.connect(options.uri).then(function(db) {
      self.db = db;
    });
  };
};