Comet (Reversing the Web with Ajax 2.0)

Web 2.0 Expo Conference

Presented by Ric Smith of Kaazing Corp


  • Comet is about pushing data to the browser
    • In short streaming
    • Useful in SSL. A lot of handshaking goes on to set up the SSL connection. The fewer times you have to do that the better.
  • Often referred to as Pending POST or Hanging GET requests

Latency = BAD

Example usage:

  • Stock Tickers
  • Meebo
  • zimbra
  • facebook chat
  • gmail


  • iframe
  • XHR Long Polling
  • XHR Streaming
  • Binary socket stream

Comet uses the java Continuation class.
Which transport to use depends on whether or not you have to deal with proxies/firewalls.

XHR Long Polling

  • not very performant

HXR Streaming

  • HTML 5 has built in support in the “event-source” tag.

Dojo has something called “cometd” which is implemented using a publish/subscribe model.

Ric demoed a javascript only instant messaging client that used the XHR streaming mechanism. No polling used. New info pushed to the browser.

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