JS to monitor data usage?

I'm building a simple html5 app to monitor the total network traffic that's incoming and outgoing. Is it possible to know your bandwidth usage using开发者_高级运维 js?

Not for the whole system -- at least not without some sort of client-side addon installed.

You could use some of the code in Firebug to do this. Firebug has a "Net" tab that monitors downloads and uploads.