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Reverse Ajax

Web Design & Development Guide

Reverse Ajax

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Reverse Ajax, not unlike DHTML, LAMP, Ajax and SPA, is not a technology in itself, but a term that refers to the use of a group of technologies together. These technologies include:

  • Ajax for handling the data on the client side in a smooth and interactive way, and passing data between server and client.
  • A technology for pushing server data to a browser
    • Comet, a connection between a server and client is kept open, by slowly loading a page in a hidden frame.
    • Piggyback, extra data is added (piggybacked) onto a normal client-server interaction.
    • Polling, the client repetitively queries (poll) the server.

Reverse Ajax is different from Ajax, as Reverse Ajax is a suite of technologies for pushing data from a server to a client. These technologies are built upon an Ajax framework.

Notes

The Polling technique is not properly a Reverse Ajax solution, because in this case the server simply responds to a repeated direct ajax request. The result is the same that Reverse Ajax, but this technique is not too elegant to be used because it makes a lot of unnecessary traffic.

Let's take a simple example:

The broadcast message.

We have 2 clients and 1 server: client1 needs to send "hello" to all the other clients


With Polling:

  • client1 sends the message "hello"
  • server receives the message "hello"
  • client2 polls the server
  • client2 receives the message "hello"
  • client1 polls the server <-- unnecessary traffic starts
  • client1 receives the message "hello"
  • client2 polls the server
  • client2 receives the message "hello" <-- unnecessary traffic continues

and these last lines repeat forever.


With Comet:

  • client1 sends the message "hello"
  • server receives the message "hello"
  • server sends the message "hello" to all clients

no unnecessary traffic.


With PiggyBack:

  • client1 sends the message "hello"
  • server receives the message "hello"
  • client2 does any request to the server
  • server adds to the response the message "hello"

no unnecessary traffic.

See also

External links

Articles
Implementations

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JavaScript library
Smart client
Reverse Ajax
Document Update Markup Language
Comparison between AJAX and Flex



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