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In my second visit to the DC PHP Developers group meeting I joined yet another over-crowded room of local programmers for this month's presentation. I really appreciate Robyn Wyrick's efforts to put these meetings together, but it's becoming clear that the venues provided by the National Press Building are faltering—a testament to the growing popularity of the group.

Jonathan Modell was tonight's presenter. A DC local, recently returning from a 10 year stint in Colorado (my home state, or more accurately I was born in Durango and then lived in Boulder for a year), Jon has extensive experience in many aspects of Web development.

His presentation focused on how he learned to integrate Ajax technology within a core PHP system. Obviously this is a hot topic, if somewhat too hot in my opinion. In a nutshell, Ajax allows you to create an HTTP request back to a server-side script, and then dynamically insert the results into your page via the DOM—all without having to POST or GET a new page (something most PHP programmers are well versed in).

Web-based applications that quietly introduced this technique are most famously associated with Google. First was "suggest" a sort of search as you type, and then Gmail and many others that began to reinvent how Web pages could improve interactivity. In truth, it was Microsoft (circa 2000) who first implemented the XMLHttpRequest (XHR) object in their version of JavaScript (jscript). Later browsers (Firefox, Safari, et al.) followed suit.

As the function implies, the traditional payload of a server-side script called by an XHR request is XML. I know of very few people that continue to do this. By far the simplest method of dynamically insterting results into your page is to use a element with a unique id, initially hidden via CSS, then grab the data returned as normal markup (for instance a set of unordered list elements), then use innerHTML to update the DOM, and finally "unhide" the element (typically a <div>). This technique is sometimes referred to as AHAH.

JSON is another lightweight technique for returning data to the requestor. It's basically serialized JavaScript in the form of name/value pairs that you eval() on the client-side for parsing and insertion into your page. In addition to JSON, the Yahoo! Developer Network set of Web services are able to return serialized PHP. Although not as applicable to an Ajax implementation, it is none-the-less an interesting method worth investigating. If there is such a beast as a JavaScript unserialize PHP function or class out there, by all means drop me a comment. For PHP developers interested in available packages for encoding and decoding JSON data, visit this comparison of PHP libraries. As of PHP version 5.2.0, JSON support is native.

In the early stages of his presentation, Jon confessed to having tested many of the Ajax JavaScript libraries that are floating around out there, and then spoke highly of his choice to use Sam Stephenson's Prototype. He is not alone, not by a long shot. There are a number of frameworks that are built on top of Prototype: RoR, Rico, and "effects" libraries that include script.aculo.us and moo.fx. PHP frameworks that include Ajax support include CakePHP and ModX.

If you are doing this sort of development work, I cannot emphasize enough how much Joe Hewitt's fantastic FireBug Firefox extension will save you hours of headaches.

To conclude his presentation, Jon demoed a social networking application that displays a calendar of events and the members who are attending, locations, dates, and so on. I had the impression that traditionalists in the audience were impressed how the page would update without the need to refresh it. But keep in mind that is the nature of asynchronous requests, there is nothing particularly new going on here, these are normal HTTP requests, they just happen to occur in the background via JavaScript and a little DOM magic to alter the page on the fly.