Express (http://expressjs.com/) is a web application framework for Node.js. It is built on top of Connect (http://www.senchalabs.org/connect/), which means that it implements middleware architecture. In the previous chapter, when exploring Node.js, we discovered the benefit of such a design decision: the framework acts as a plugin system. Thus, we can say that Express is suitable for not only simple but also complex applications because of its architecture. We may use only some of the popular types of middleware or add a lot of features and still keep the application modular.

In general, most projects in Node.js perform two functions: run a server that listens on a specific port, and process incoming requests. Express is a wrapper for these two functionalities. The following is basic code that runs the server:

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');...