Older browsers don't support WebSockets. So in order to provide a similar experience, we need to fall back to various browser/plugin-specific techniques to emulate WebSocket functionality to the best of the deprecated browser's ability.
Naturally, this is a mine field, requiring hours of browser testing and in some cases highly specific knowledge of proprietary protocols (for example, IE's Active X htmlfile object).
socket.io provides a WebSocket-like API to the server and client to create the best-case real-time experience across a wide variety of browsers, including old (IE 5.5+) and mobile (iOS Safari, Android) browsers.
On top of this, it also provides convenience features, such as disconnection discovery allowing for auto reconnects, custom events, namespacing, calling callbacks across the wire (see the next recipe Callbacks over socket.io transport), as well as others.
In this recipe, we will re-implement the previous task for a high compatibility...