app.js

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var mongodb = require('mongodb');
var index = require('./routes/index');
var users = require('./routes/users');
//mongoose.connection.on('open',()=>{
  //console.log('Connected to mongodb.');
  //mongoose.connection.db.listCollections().toArray(function (err,names) {
    //console.log(names);
var app = express();
// view engine setup
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'hbs');
// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
//app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', index);
app.use('/users', users);
//mongoose
app.use(function(req,res,next){
    req.db = db;
    next();
});
app.get('/book',function (req,res) {
    book.find({})
        .exec(function(err,books){
          if(err){
            res.send('error has occured');
          }else{
            console.log(books);
            res.json(books);
          }
        })
});
// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});
// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};
  // render the error page
  res.status(err.status || 500);
  res.render('error');
});
var db = 'localhost:27017';
mongoose.Promise = global.Promise;
var book = require('./bookmodel.js');
mongoose.createConnection(db, err => {
    console.log(err ||  `MongoDB connected at ${db}`);
});

module.exports = app;

bookmodel.js

/**
 * Created by gunnerhatmaker on 7/31/17.
 */
var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var bookSchema = new Schema({
title: String,
    author: String,
    category: String
});

module.exports = mongoose.model('Book',bookSchema);

packages.json

{
  "name": "untitled",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./bin/www"
  },
  "dependencies": {
    "body-parser": "~1.17.1",
    "cookie-parser": "~1.4.3",
    "debug": "~2.6.3",
    "express": "^4.15.4",
    "hbs": "~4.0.1",
    "mongodb": "^2.2.31",
    "mongoose": "^4.11.8",
    "morgan": "~1.8.1",
    "serve-favicon": "~2.4.2"
  },
  "devDependencies": {
    "nodemon": "^1.11.0"
  }
}

www.js

#!/usr/bin/env node

/**
 * Module dependencies.
 */

var app = require('../app');
var debug = require('debug')('untitled:server');
var http = require('http');

/**
 * Get port from environment and store in Express.
 */

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

/**
 * Create HTTP server.
 */

var server = http.createServer(app);

/**
 * Listen on provided port, on all network interfaces.
 */

server.listen(port);
server.on('error', onError);
server.on('listening', onListening);

/**
 * Normalize a port into a number, string, or false.
 */

function normalizePort(val) {
  var port = parseInt(val, 10);

  if (isNaN(port)) {
    // named pipe
    return val;
  }

  if (port >= 0) {
    // port number
    return port;
  }

  return false;
}

/**
 * Event listener for HTTP server "error" event.
 */

function onError(error) {
  if (error.syscall !== 'listen') {
    throw error;
  }

  var bind = typeof port === 'string'
    ? 'Pipe ' + port
    : 'Port ' + port;

  // handle specific listen errors with friendly messages
  switch (error.code) {
    case 'EACCES':
      console.error(bind + ' requires elevated privileges');
      process.exit(1);
      break;
    case 'EADDRINUSE':
      console.error(bind + ' is already in use');
      process.exit(1);
      break;
    default:
      throw error;
  }
}

/**
 * Event listener for HTTP server "listening" event.
 */

function onListening() {
  var addr = server.address();
  var bind = typeof addr === 'string'
    ? 'pipe ' + addr
    : 'port ' + addr.port;
  debug('Listening on ' + bind);
}