How to send a query to the browser from time to time?

[Admin]

I am creating a chat application like Messenger for the web (using the  
browser) and I'm wondering if there is a way to receive new messages from  
time to time from the server other than refreshing the page each 5 sec.

If there were a way to have the server-side application send new messages  
to the browser this would be awesome because it would save dramatically on  
bandwidth. The application would consume bandwidth only when there are new  
messages. There would be no communication client-server until people write  
a new message.

Do you know if it's possible?

-- 
Thanks,

Admin.
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