Thanks Yahoo for the new rule. =)

"This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612"

Does that work across all browsers? I was under the impression that IE would never cache a HTTPXMLRequest response that has a parameter in it's URL. I haven't tested it, though..

Also, Wikipedia indicates that IE and Firefox use caching header differently (http://en.wikipedia.org/wiki/XMLHttpRequest#Caching). Is this the case?

If you _don't_ want the XHR to be cached, you can modify the querystring, as seen in this example:
http://stevesouders.com/hpws/xhr-beacon.php

If you _do_ want the XHR to be cached, you can still include a querystring, but the parameters must stay the same, as seen in this example:
http://stevesouders.com/hpws/xhr-cached.php

In that example the XHR URL has a querystring, and yet it is still read from cache in both Firefox and IE. In order for the XHR to be cached, you have to do more than simply keep the URL constant. You also have to provide a future Expires or Cache-Control header, as explained in Rule 3.

It's likely that the person who wrote the Wikipedia article did not provide the necessary headers for the XHR to be cached. Or perhaps it was an older version of Firefox (I'm on Firefox 2.0, but am sure Firefox 1.5 behaves the same). Finally, it's possile they had changed their browser cache settings or were running a utility like Fasterfox that altered the typical behavior of Firefox. Bottomline: Firefox does cache XHR responses if the URL is the same and the headers set the expiration date in the future.

thanx :)

Keep me updated!

Isn't it a bad idea to make the addressbook cacheable on the browser since it may contain
user's private inforamtion? We may be better off having a server side cache that
authenticates the request with user cookies and serves the response back fast. just a
thought.

Data privacy is critical whenever thinking about caching. Each application must decide how to handle privacy issues. In my opinion, confidential information should be transmitted using SSL. I'll point out that the Web 2.0 versions of Google Mail and Yahoo! Mail do not have a single https request. The ideal situation, in my mind, would be to transmit over SSL and give the user the option about caching. Since I'm the only user on my PC, I would opt-in for caching. Fortunately, caching of https responses is supported in IE.

-Steve

thanks for your rules,they help me much:)
But there is a problem,for a mail user,his client,ie,etc. need to post request to server timely so it can know whether there is a new mail coming. How to reduce these kind of request?Or whether there is someway that server can push some data to the client without using long-connecting?thx:)

We here at Siderean have been devotees of YUI since its inception. Most of the library has proven its worth. However, regarding cacheable XHR objects, we've tried your web page on IE6, IE7, as well as FF2.0.0.11. We've also tested on Mac OS X running FF 2.0.0.11. All tests of the web page seemed to have failed - i.e. the dialogue "The XMLHttpRequest was sent" appears. Has something changed in the caching mechanism ?

Not to beleaguer the point, but we have confirmed the dialogue using http packet sniffers.

Hi, Riley. Don't use the dialog box as an indicator of HTTP traffic. Instead, use a packet sniffer, as suggested in the instructions. The dialog box is just telling you that an XHR was executed. Even though the XHR is executed, on subsequent requests it's read from cache, which is the point of that demo page. To make it clearer I changed the message to say "The XMLHttpRequest was executed, but it MIGHT have been read from the browser's cache. Use a packet sniffer to see." When I run the demo (http://stevesouders.com/hpws/xhr-cached.php) on Firefox and IE with a packet sniffer I see that the second XHR is in fact read from cache.

-Steve

Gopal@, You probably want to use "Cache-Control: private" to cache user specific content.

I would like to open up a web site but i kind of luck knowledge of how to open or get one so pliz hlep me out in ma problem if yo to hlep send the data to my e-mail address.Thanks its been good jazzing with you

I was trying to implement this in my personal website http://www.rahulnimawat.com but there a dialog box comes up stating: "the xml parser expired" Please suggest me about this error and how to remove it.