is it possible to use javascript instead of silverligt for duplex binding?

Question

I want to ask some question about WCF duplex services.

 

There is a sample program in this link.

http://www.silverlightshow.net/items/The-duplex-story-looking-at-duplex-communication-in-Silverlight-4-Part-1.aspx

Is it possible to use javascript instead of silverlight for duplex binding? And is running a callback function in the javascript file from server side possible. Like silverlight.

 

We want to show who is online and how many people are there in the our web site.

We want to update this information on the web site immediatly when someone enters the web site.

 

 

thanks