Asynchronous Javascript and XML, is a method used to communicate with the server and load new content in a website without having to reload the page. You’ve probably seen it all over the web, and now you are going to learn how to implement it yourself!

Step 1: Install JQuery: Not sure what jquery is? It is basically a bunch a prebuilt javascript to make your life a whole lot easier. Go to http://code.google.com/p/jqueryjs/downloads/detail?name=jquery-1.3.2.min.js to download the most stable version of JQuery as of this post publishing date (1.3.2) or http://jquery.com/ for the most recent version (1.4.2).

Step 2: Install JQuery UI For Better Animations (optional): I highly advise using some animations to spice up the interaction of your AJAX. When a user clicks something that fires your AJAX, they want to know something is happening. If it happens too quickly, they won’t know, so we’ll actually have to slow it down a bit for them. Visit http://jqueryui.com/download to download the UI components if you’d like these better animations. I advise the “core”, the “effects core”, and the “effects blind”. You can try other effects as well such as “fold” if you want a different visual.

Step 3: Make Two Different Pages: The concept of AJAX relies on the existence of two files. The first file is a normal webpage that will contain whatever you want to reload. The second file should use HTML, but not be contained within any html or body tags. The reason for this is your the javascript you are about to create will be loading the entire second document literally within the first document. You can’t have two html or body tags, so don’t use them! Having trouble understanding, well how about an example.  Say you are creating a search feature on your site. The first document is the actual search page that contains the search bar and submit button (say http://samplesite.com/search.html). The second document will hold the results of the search that was submitted on the first page and usually takes some sort of arguments, variables, query strings, or whatever else you’d like to call them (in the case of this example, probably the search terms entered in the search bar).

The HTML for the first document (front-facing):

<img id="loadImg" src="animatedGifLocation" alt="Loading..." />
<div id="opacityWrap"><div id="fillBox"></div></div>
<input id="queryField" type="text" value="" />
<input id="submitQueryButton" type="button" value="Submit Query" />

The PHP for the second document (hidden from users):

<?php
  $textBoxContent = $_GET['data'];
  echo ("<p>".$textBoxContent."</p>");
?>

Step 4: Write Some Javascript: Using some preexisting jquery functions, all we have to do is throw together a simple function that is called on the button click (or whatever else works for your particular situation). This particular javascript below uses an animated gif to indicate loading and a div two grey out the loading content box.

$("#submitQueryButton").click(function() {
  $("#opacityWrap").animate({ opacity: .15 }, 100);
  $("#loadImg").show();
  $("#fillBox").load("secondPageURLhere?query=" + $("#queryField").val(),function() {
    $("#loadImg").hide();
    $("#opacityWrap").animate({ opacity: 1.0 }, 100);
  });
});

Step 5: See It In Action:

Dependent on whether you enter a number or a word into the text box, different content will load here. The button calls an AJAX function that loads another page. This page, dependent on the request sent by the AJAX, outputs the page’s determination of what you entered.

The most useful time for this implementation of AJAX is when you want to communicate with your database to load content that your already rendered page doesn’t have. This particular example does not actually use any information from a database, but it should get the point across. So now that you know how to implement this, go and do it! Ask questions if you got ‘em.