2009/6/23 Aamchi <aman.ra...@googlemail.com>

> Hi,
> I was wondering if Ajax.PeriodicalUpdater can detect if content has
> changed since the last update and if so trigger an event.
> So for example I have a scoreboard which fetches data every 5 seconds
> and displays this. I would be cool if there could be some kind of
> notification if content had changed. I know that the new content is
> stores in responseText but how can I compare it to the previous
> content...
> Thanks,
> Aman
> >
Personally, I would do this server side.
Assuming you get the data in some sort of structure before either rending
some HTML and sending it or just sending it JSON'd, then you should be able
to build a hash of the data.

See [1] for info on Hash Functions.

So. If you sent the hash value in a X-JSON header along with an onSuccess()
callback, you can extract the hash from the second param to the onSuccess
and compare this with the previously retrieved hash to indicate you've got
changed data. See [2] for details about PeriodicalUpdater update
notification and [3] for the parameters to common callbacks.



[1] http://en.wikipedia.org/wiki/Hash_function
[2] http://www.prototypejs.org/api/ajax/periodicalUpdater

Richard Quadling
Zend Certified Engineer : http://zend.com/zce.php?c=ZEND002498&r=213474731
"Standing on the shoulders of some very clever giants!"

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