var express = require('express');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var session = require('express-session');
var MongoStore = require('connect-mongo')(session);
var app = express();

var port = process.env.PORT || 3000;

mongoose.connect(process.env.MONGOLAB_URI || 'mongodb://localhost/foobar');

// mongodb connection
mongoose.connect("mongodb://localhost:27017/pingpong");
var db = mongoose.connection;
// mongo error
db.on('error', console.error.bind(console, 'connection error:'));


// use sessions for tracking logins
app.use(session({
  secret: 'treehouse loves you',
  resave: true,
  saveUninitialized: false,
  store: new MongoStore({
    mongooseConnection: db
  })
}));

// make user ID available in templates
app.use(function (req, res, next) {
  res.locals.currentUser = req.session.userId;
  next();
});

// parse incoming requests
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));

// serve static files from /public
app.use(express.static(__dirname + '/public'));

// view engine setup
app.set('view engine', 'pug');
app.set('views', __dirname + '/views');

// include routes
var routes = require('./routes/index');
app.use('/', routes);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('File Not Found');
  err.status = 404;
  next(err);
});

// error handler
// define as the last app.use callback
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});

// listen on port 3000
app.listen(3000, function () {
  console.log('Express app listening on port 3000');
});


In addition, here are my heroku logs:

2017-09-24T18:50:56.086372+00:00 app[web.1]:   message: 'failed to connect to server [localhost:27017] on first connect [MongoError: connect ECONNREFUSED 127.0.0.1:27017]' }
2017-09-24T18:50:56.086371+00:00 app[web.1]:   name: 'MongoError',