Ever since the onset of web applications, developers have worked towards different ways of getting duplex communication between the server and the browser. Be it using Java, Flash, Comet, or many other workarounds, all aim to do the same. But for the first time, there is a specification to build a full-duplex communication system by using HTML5 WebSockets. WebSocket is a revolutionary, new communication feature in the HTML5 specification that defines a full-duplex communication channel operating over the Web through a single socket.

Although the WebSockets RFC is published, it is not, and will never be, available on older browsers that are still in use. Socket.io is an abstraction layer for WebSockets, with Flash, XHR, JSONP, and HTMLFile fallbacks. Socket.io provides an easy server and client library for making real-time, streaming updates between a web server and a browser client.

Socket.io is a node module available through the npm, and we will add it to our package dependencies. The current release of socket.io is 0.9.10. To add this to our dependencies, add the following line to the dependencies object in package.json:

    "socket.io": "0.9.10"

And install it using the npm:

$ npm install

This will bring socket.io in the node_modules folder. Now let's see how we will use it.