Installing Node.js

Node.js is a command-line tool. After installing it, the node command will be available on our terminal. The node command accepts several arguments, but the most important one is the file that contains our JavaScript. Let's create a file called server.js and put the following code inside:

var http = require('http');
http.createServer(function (req, res) {
   res.writeHead(200, {'Content-Type': 'text/plain'});
   res.end('Hello World\n');
}).listen(9000, '127.0.0.1');
console.log('Server running at http://127.0.0.1:9000/');

If you run node ./server.js in your console, you will have the Node.js server running. It listens for incoming requests at localhost (127.0.0.1) on port 9000. The very first line of the preceding code requires the built-in http module. In Node.js, we have the require global function that provides the mechanism to use external modules. We will see how to define our own modules in a bit. After that, the scripts continue with the createServer and listen methods on the http module. In this case, the API of the module is designed in such a way that we can chain these two methods like in jQuery.

The first one (createServer) accepts a function that is also known as a callback, which is called every time a new request comes to the server. The second one makes the server listen.

The result that we will get in a browser is as follows: