The problem with this approach is, in some applications, the web browser needs to constantly poll the server to check for updates. Examples of this include Email (e.g. notification when you get a new email) and Instant Messaging. Events in these applications are not always user-generated. Currently this is problem is solved by the application checking for updates on the server at a predefined interval (e.g. 30 seconds). This places a huge burden on the web server.
Introducing Web 3.0: The event-driven web. With Web 3.0, the 30-second poll is no longer required! Instead, the browser maintains a persistent HTTP connection to the web server. The web server uses this connection to throw events at the browser as required!
There's already a suitable spec out: Server-sent DOM events. Take a look at the <event-source> element.
- Reduced server load - One connection per client, no overhead of serving polled connections
- Instant delivery - e.g. of Emails and instant messages
- Poor browser support. At the moment, I think only Opera supports <event-source>.