title: why use http.createSever in express app?
body: <p>I found in express api documentation, this is how one creates new express server</p>
  
  <pre><code>var express = require('express');
  var app = express();
  
  app.listen(3000);
  </code></pre>
  
  <p>it works properly but when you create a new app using express by default it generate following code to create new server </p>
  
  <pre><code> var express = require('express');
   var app = express();
      http.createServer(app).listen(app.get('port'), function(){
        console.log("Express server listening on port " + app.get('port'));
      });
  </code></pre>
  
  <p>can someone explain me why express using http createServer method here.  </p>