How can I connect to mongodb using express without mongoose?

Following the example from my comment, modifying it so that the app handles errors rather than failing to start the server.

var express = require('express');var mongodb = require('mongodb');var app = express();var MongoClient = require('mongodb').MongoClient;var db;// Initialize connection onceMongoClient.connect("mongodb://localhost:27017/integration_test", function(err, database) {  if(err) return console.error(err);  db = database;  // the Mongo driver recommends starting the server here because most apps *should* fail to start if they have no DB.  If yours is the exception, move the server startup elsewhere. });// Reuse database object in request handlersapp.get("/", function(req, res, next) {  db.collection("replicaset_mongo_client_collection").find({}, function(err, docs) {    if(err) return next(err);    docs.each(function(err, doc) {      if(doc) {        console.log(doc);      }      else {        res.end();      }    });  });});app.use(function(err, req, res){   // handle error here.  For example, logging and returning a friendly error page});// Starting the app here will work, but some users will get errors if the db connection process is slow.    app.listen(3000);  console.log("Listening on port 3000");

var mongodb = require('mongodb');var uri = 'mongodb://localhost:27017/dbname';module.exports = function(callback) {  mongodb.MongoClient.connect(uri, callback);};

Ad this snippet in a file say connect.js and then require this file(connect.js) in your file where you are declaring your functions for http requests.