what should be inside app.js for server to run by default

default app.js

var express = require('express'); // require express module 
var app = express();              // references and creates a new express app
var serv = require('http').Server(app); //require http module with express application info
app.get('/', function(req, res) {
  res.sendFiles(__dirname + '/client/index.html');
});
app.use('/client', express.static(__dirname + '/client'));
serv.listen(2000);
console.log("Server started.");