text: var createError = require('http-errors');
  var express = require('express');
  
  //Set up mongoose connection
  var mongoose = require('mongoose');
  // Set up mongoose connection
  var dev_db_url = 'mongodb+srv://ZarthaxX:tejasrotas1@cluster0-pdetb.azure.mongodb.net/local_library?retryWrites=true&w=majority';
  var mongoDB = process.env.MONGODB_URI || dev_db_url;
  
  mongoose.connect(mongoDB, { useNewUrlParser: true , useUnifiedTopology: true });
  var db = mongoose.connection;
  db.on('error', console.error.bind(console, 'MongoDB connection error:'));
  var path = require('path');
  var cookieParser = require('cookie-parser');
  var logger = require('morgan');
  
  var indexRouter = require('./routes/index');
  var usersRouter = require('./routes/users');
  var catalogRouter = require('./routes/catalog',catalogRouter); // Add catalog routes to middleware chain.
  var compression = require('compression');
  var helmet = require('helmet');
  
  // Create the Express application object
  var app = express();
  
  app.use(helmet());
  
  // view engine setup
  app.set('views', path.join(__dirname, 'views'));
  app.set('view engine', 'pug');
  
  app.use(logger('dev'));
  app.use(express.json());
  app.use(express.urlencoded({ extended: false }));
  app.use(cookieParser());
  app.use(express.static(path.join(__dirname, 'public')));
  
  app.use(compression());
  
  app.use('/', indexRouter);
  app.use('/users', usersRouter);
  app.use('/catalog', catalogRouter); // Add catalog routes to middleware chain.
  // catch 404 and forward to error handler
  app.use(function(req, res, next) {
    next(createError(404));
  });
  
  // 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');
  });
  
  module.exports = app;
  