How to deploy NodeJS App to Heroku?

I am creating a chat app with NodeJS, and I want to deploy to Heroku. However, I get an error: An error occurred in the application and your page could not be served. If you are the application owner, check your logs for details. by using the Github deployment. Does anyone know what is going on?

Here is some code to see what I have done.

    {
  "name": "chat",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./lib/index.js",
    "test": "jasmine"
  },
  "dependencies": {
    "express": "~4.13.1",
    "firebase": "^3.9.0",
    "request-promise": "^2.0.1",
    "socket.io": "^1.4.5"
  },
  "devDependencies": {
    "jasmine-sinon": "^0.4.0",
    "jscs": "^2.11.0",
    "proxyquire": "^1.7.4",
    "rewire": "^2.5.1",
    "sinon": "^1.17.3"
  }
}

index.js (Server)

    var express = require('express');
var app = express();
var path = require('path');
var http = require('http').Server(app);
var io = require('socket.io')(http);

var routes = require('./routes');
var chats = require('./chat');



app.use(express.static(path.join(__dirname, '../public')));

routes.load(app);
chats.load(io);


var port = process.env.PORT || 3000;
app.listen(port);
console.log('Server is listening at port:' + port); 

via Suzy Hakobyan