My project uses the Prototype library (http://www.prototypejs.org/api/ajax/periodicalUpdater), and I'm using this code:

Code:
new Ajax.PeriodicalUpdater(‘activity’, ‘activity.output.php’, { method: ‘get’, frequency: 1, decay: 2, insertion: Insertion.Top });
In order to grab new content and insert it into the top of an un-ordered list. Naturally, I only want items to be added to the list if they are new... so how exactly do I go about making Ajax.PeriodicalUpdater only update if the result of activity.output.php is new?

The decay already works nicely, slowing down the updates if new content does not seem to arrive for a while... but it still creates the same item on the list over and over again (until the content of activity.output.php changes).

Any help is appreciated, thanks!