There is also a Form.observer 
http://www.prototypejs.org/api/timedObserver/form-observer
I used to use this but implemented my own version of it with a cache and 
some hashing, it didnt take long to write and works perfectly

HTH
Alex


----- Original Message ----- 
From: "Aamchi" <aman.ra...@googlemail.com>
To: "Prototype & script.aculo.us" <prototype-scriptaculous@googlegroups.com>
Sent: Tuesday, June 23, 2009 11:19 PM
Subject: [Proto-Scripty] Re: Periodical Updater detect content change



Thanks, for your response. I'm not 100% sure if I understand correctly
what you mean. If I get some data and generate a hash and write this
to the JSON header and retrieve this when calling onSuccess, how will
I still have the previous hash? From where will I get this?  Won't the
updated data cause the hash to be overwritten in the JSON header? Or
do I have to send two hashes always and compare them?

On 23 Jun., 22:57, Richard Quadling <rquadl...@googlemail.com> wrote:
> 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.
>
> Regards,
>
> Richard.
>
> [1]http://en.wikipedia.org/wiki/Hash_function
> [2]http://www.prototypejs.org/api/ajax/periodicalUpdater
> <http://www.prototypejs.org/api/ajax/periodicalUpdater>[3]http://www.prototypejs.org/api/ajax/options
> <http://www.prototypejs.org/api/ajax/options>
>
> --
> -----
> 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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