XML Reference Guide

Mar 14, 2003

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While all of the principles that make Ajax work have been around for some time, the method of putting them all together is fairly new, so some growing pains are bound to erupt. In fact, if you followed our series on building an Ajax feed reader, the word "pain" may have been foremost in your mind.

I mean, sure, it's powerful, but making it happen is a lot of work. Maintaining asynchronous connections, callback functions and of course the dreaded "browser differences" issue... it's enough to make you wonder why somebody hasn't simplified this and created a library already.

Well, of course someone has. The Simple Ajax (SAJAX) library enables you to call server-side functions directly from the browser.

Well, almost directly.

For example, we can take our feed reader page and use SAJAX to simplify the process of requesting information. We have three "actions" to perform:

When the user clicks a top-level directory, display the subcategories in the "sub" div.
When the user clicks a subcategory, display the list of feeds in the "feedlist" div.
When the user clicks a feed, retrieve the feed and the XSLT stylesheet and display the transform data in a "feed" div.

Let's start by putting together the framework. First, we have the page itself:

<html>

<head>

<style type="text/css">
span {font-weight: bold; color: blue; text-decoration: underline}
#feed {font-size: smaller}
</style>


       <script type="text/javascript">

        function getSubcategory(catId){
		alert(catId);
        }

</script>

</head>
<body>

<table width="100%" border="0">
<tr>
   <td id="main" width="200" valign="top"><h3>Main categories</h3>

<span onclick="getSubcategory(1)">Arts</span> (608)</br />
<span onclick="getSubcategory(2)">Business</span> (152)</br />
<span onclick="getSubcategory(3)">Comics</span> (21)</br />

<span onclick="getSubcategory(4)">Computers</span> (202)</br />
<span onclick="getSubcategory(5)">Games</span> (29)</br />
<span onclick="getSubcategory(6)">Health</span> (35)</br />

<span onclick="getSubcategory(7)">Home</span> (3)</br />
<span onclick="getSubcategory(8)">News</span> (66)</br />
<span onclick="getSubcategory(9)">Recreation</span> (21)



</td>
   <td width="200" valign="top"><h3>Sub categories</h3>

      <div id="sub"></div>

   </td>

   <td rowspan="2" valign="top"><div id="status"></div>
         <div id="feed"></div></td>
</tr>
<tr>
   <td colspan="2"><h3>Feeds</h3>

       <div id="feedlist"></div>

   </td>
</tr>
</table>

</body>
</html>

Here we see the HTML page with the divs defined, and with the getSubcategory() script in place. That script needs to retrieve a list of categories, which come from a PHP function:

<?

	function subcategories($cat_id){
		return "Subcat for ".$cat_id;
	}

?>
<html>
<head>

<style type="text/css">
span {font-weight: bold; color: blue; text-decoration: underline}
#feed {font-size: smaller}

</style>


       <script type="text/javascript">

        function getSubcategory(catId){
		alert(catId);
        }
	
</script>

</head>
<body>

<table width="100%" border="0">
<tr>
   <td id="main" width="200" valign="top"><h3>Main categories</h3>

<span onclick="getSubcategory(1)">Arts</span> (608)</br />

...

In a moment will add some actual code, but the goal here is to show the calling of the function, not the function itself.

Okay, now we have the script in the page, so we have to hook the two together. Download the SAJAX package and place the Sajax.php file in the same directory as your page.

The way we create a "hook" to the PHP function is to "export" the functions want to make available. In this case, that means:

<?

	function subcategories($cat_id){
		return "Subcat for ".$cat_id;
	}

	require("Sajax.php");
    
        sajax_init();
        sajax_export("subcategories");

        sajax_handle_client_request();

?>
<html>
<head>

...

Now we can call the function from the JavaScript. To do that, we actually need two JavaScript functions for each PHP function. The first calls the exported function, and the second is the callback function to which the exported function sends its results. For example:

<?

	function subcategories($cat_id){
		return "Subcat for ".$cat_id;
	}

	require("Sajax.php");
    
    	sajax_init();
    	sajax_export("subcategories");

        sajax_handle_client_request();

?>
<html>
<head>

<style type="text/css">
span {font-weight: bold; color: blue; text-decoration: underline}
#feed {font-size: smaller}
</style>


       <script type="text/javascript">

        <?
        sajax_show_javascript();
        ?>
	
        function getSubcategory_cb(list) {
                document.getElementById('sub').innerHTML = list;
        }
        function getSubcategory(catId){
	    x_subcategories(catId, getSubcategory_cb);
        }
	
</script>

</head>
<body>

<table width="100%" border="0">
<tr>
   <td id="main" width="200" valign="top"><h3>Main categories</h3>

<span onclick="getSubcategory(1)">Arts</span> (608)</br />

<span onclick="getSubcategory(2)">Business</span> (152)</br />
<span onclick="getSubcategory(3)">Comics</span> (21)</br />
...

</td>

   <td width="200" valign="top"><h3>Sub categories</h3>

      <div id="sub"></div>

   </td>
   <td rowspan="2" valign="top"><div id="status"></div>

         <div id="feed"></div></td>
</tr>
...

When the user clicks a category link, the JavaScript getSubcategory function calls x_subcategories, the exported version of the PHP subcategories function. The x_subcategories function takes the category ID and the function to which it should send the results, getSubcategories_cb. That function takes the results and displays them, as you can see in figure 1.

Basic page

We can do the same thing for the other functions:

<?

	function subcategories($cat_id){
		return "Subcat for ".$cat_id;
	}

	function feeds($cat_id){
		return "Feeds for ".$cat_id;
	}

	function proxy($feed_url){
		return "Proxy for ".$feed_url;
	}

	require("Sajax.php");
    
     	sajax_init();
     	sajax_export("subcategories");
  	sajax_export("feeds");
     	sajax_export("proxy");

        sajax_handle_client_request();

?>
<html>
<head>

<style type="text/css">
span {font-weight: bold; color: blue; text-decoration: underline}
#feed {font-size: smaller}
</style>


       <script type="text/javascript">

       <?
        sajax_show_javascript();
        ?>
	
        function getSubcategory_cb(list) {
                document.getElementById('sub').innerHTML = list;
        }
        function getSubcategory(catId){
	    x_subcategories(catId, getSubcategory_cb);
        }
	

        function getFeeds_cb(list) {
                document.getElementById('feedlist').innerHTML = list;
        }
        function getFeeds(catId){
                x_feeds(catId, getFeeds_cb);
        }

        function loadFeed_cb(feedStream){
                document.getElementById('feed').innerHTML = feedStream;
        }
        function loadFeed(feedURL){
                x_proxy(feedURL, loadFeed_cb);
        }
</script>

</head>
<body>
...

Now we can start adding the actual code. Again, the important thing is not so much what the functions are doing, but that they're being called, so we can just have them output the results:

<?

	function subcategories($cat_id){
         if ($cat_id == 1){

             return "<span onclick='getFeeds(100)'>Animation</span> (1)<br />".
             "<span onclick='getFeeds(101)'>Architecture</span> (1)<br />".
             "<span onclick='getFeeds(102)'>Comics</span> (3)<br />".
             "<span onclick='getFeeds(103)'>Digital</span> (1)<br />".
             "<span onclick='getFeeds(104)'>Entertainment</span> (0)<br />".
             "<span onclick='getFeeds(105)'>Science Fiction</span> (2)<br />".
             "<span onclick='getFeeds(106)'>Literature</span> (2)<br />".
             "<span onclick='getFeeds(107)'>Movies</span> (9)<br />".
             "<span onclick='getFeeds(108)'>Music</span> (292)<br />".
             "<span onclick='getFeeds(109)'>Online_Writing</span> (3)<br />".
             "<span onclick='getFeeds(110)'>People</span> (255)<br />".
             "<span onclick='getFeeds(111)'>Radio</span> (1)<br />".
             "<span onclick='getFeeds(112)'>Television</span> (37)<br />".
             "<span onclick='getFeeds(113)'>Writers_Resources</span> (1)<br />";

	   } else if ($cat_id == 2) {

             return "Cat 2, Subcat 1<br />Cat 2, Subcat 2<br />Cat 2, Subcat 3<br />Cat 2, Subcat 4<br />Cat 2, Subcat 5<br />Cat 2, Subcat 6<br />Cat 2, Subcat 7<br />Cat 2, Subcat 8<br />Cat 2, Subcat 9<br />Cat 2, Subcat 10<br />";

         } else  { 

             return "Cat 3, Subcat 1<br />Cat 3, Subcat 2<br />Cat 3, Subcat 3<br />Cat 3, Subcat 4<br />Cat 3, Subcat 5<br />Cat 3, Subcat 6<br />Cat 3, Subcat 7<br />at 3, Subcat 8<br />Cat 3, Subcat 9<br />Cat 3, Subcat 10<br />";

	   } ...

	}

	function feeds($cat_id){
		return '<br />

             <span onclick="loadFeed(\'http://www.vanguardreport.com/phpnuke/backend.php\')">The Vanguard Science Fiction Report</span><br />
             <span onclick="loadFeed(\'http://www.nicholaschase.com/blog/index.rdf\')">Chaos Magnet</span><br />';
	}

	function proxy($feed_url){
            return file_get_contents($feed_url);
	}

	require("Sajax.php");
    
     	sajax_init();
     	$sajax_debug_mode = 1;
     	sajax_export("subcategories");
     	sajax_export("feeds");
     	sajax_export("proxy");
...

At this point, you should be able to request a list of categories and feeds, and display a raw feed. But what about transforming the feed?

Well, you can do that on the server-side, or on the client side. To do it on the server-side, you'd simply modify the proxy function to perform the transformation before returning the results.

That, however, assumes that your server can perform transformations, and in this case -- rented space on a shared server -- that's not true. So instead, were going to handle it as we did before, loading both the stylesheet and the raw feed and transforming it in the browser:

<?

	function subcategories($cat_id){
	   if ($cat_id == 1){

             return "<span onclick='getFeeds(100)'>Animation</span> (1)<br />".
             "<span onclick='getFeeds(101)'>Architecture</span> (1)<br />".
             "<span onclick='getFeeds(102)'>Comics</span> (3)<br />".
             "<span onclick='getFeeds(103)'>Digital</span> (1)<br />".
             "<span onclick='getFeeds(104)'>Entertainment</span> (0)<br />".
             "<span onclick='getFeeds(105)'>Science Fiction</span> (2)<br />".
             "<span onclick='getFeeds(106)'>Literature</span> (2)<br />".
             "<span onclick='getFeeds(107)'>Movies</span> (9)<br />".
             "<span onclick='getFeeds(108)'>Music</span> (292)<br />".
             "<span onclick='getFeeds(109)'>Online_Writing</span> (3)<br />".
             "<span onclick='getFeeds(110)'>People</span> (255)<br />".
             "<span onclick='getFeeds(111)'>Radio</span> (1)<br />".
             "<span onclick='getFeeds(112)'>Television</span> (37)<br />".
             "<span onclick='getFeeds(113)'>Writers_Resources</span> (1)<br />";

	   } else if ($cat_id == 2) {

             return "Cat 2, Subcat 1<br />Cat 2, Subcat 2<br />Cat 2, Subcat 3<br />Cat 2, Subcat 4<br />Cat 2, Subcat 5<br />Cat 2, Subcat 6<br />Cat 2, Subcat 7<br />Cat 2, Subcat 8<br />Cat 2, Subcat 9<br />Cat 2, Subcat 10<br />";

         } else  { 

             return "Cat 3, Subcat 1<br />Cat 3, Subcat 2<br />Cat 3, Subcat 3<br />Cat 3, Subcat 4<br />Cat 3, Subcat 5<br />Cat 3, Subcat 6<br />Cat 3, Subcat 7<br />at 3, Subcat 8<br />Cat 3, Subcat 9<br />Cat 3, Subcat 10<br />";

         }

	}

	function feeds($cat_id){
		return '<br />

             <span onclick="loadFeed(\'http://www.vanguardreport.com/phpnuke/backend.php\')">The Vanguard Science Fiction Report</span><br />
             <span onclick="loadFeed(\'http://www.nicholaschase.com/blog/index.rdf\')">Chaos Magnet</span><br />';
	}

	function proxy($feed_url){
            return file_get_contents($feed_url);
	}

	require("Sajax.php");
    
      sajax_init();
      sajax_export("subcategories");
      sajax_export("feeds");
      sajax_export("proxy");

      sajax_handle_client_request();

?>
<html>
<head>

<style type="text/css">
span {font-weight: bold; color: blue; text-decoration: underline}
#feed {font-size: smaller}
</style>


       <script type="text/javascript">

       <?
        sajax_show_javascript();
        ?>
	
        function getSubcategory_cb(list) {
                document.getElementById('sub').innerHTML = list;
        }
        function getSubcategory(catId){
	    x_subcategories(catId, getSubcategory_cb);
        }
	

        function getFeeds_cb(list) {
                document.getElementById('feedlist').innerHTML = list;
        }
        function getFeeds(catId){
                x_feeds(catId, getFeeds_cb);
        }


        var styleLoaded = false;
        var feedLoaded = false;
	var rawFeed = null;
        var styleSheet = null;

        function loadFeed_cb(feedStream){
            rawFeed = feedStream;
	    feedLoaded = true;
            if (styleLoaded){
		    transformFeed();
	    }
        }
        function loadStyle_cb(styleStream){
            styleSheet = styleStream;
            styleLoaded = true;
            if (feedLoaded){
		  transformFeed();
            } 
        }
        function loadFeed(feedURL){
                x_proxy(feedURL, loadFeed_cb);
                x_proxy("http://www.nicholaschase.com/ajaxdemo/rss1.xsl", loadStyle_cb);
        }

        function transformFeed(){

          if (window.XMLHttpRequest){

           	var dp = new DOMParser();
           	theDocument = dp.parseFromString(rawFeed, "text/xml");

           	var dp2 = new DOMParser();
           	stylesheetDoc = dp2.parseFromString(styleSheet, "text/xml");
                var xsltProcessor = new XSLTProcessor();
                xsltProcessor.importStylesheet(stylesheetDoc);
                response = xsltProcessor.transformToFragment(theDocument, document);

                destinationDiv = document.getElementById("feed");
                destinationDiv.innerHTML = "";
                destinationDiv.appendChild(response);

		feedLoaded = false;
		rawFeed = null;

          } else if (window.ActiveXObject) {

           	stylesheetDoc = new ActiveXObject("Microsoft.XMLDOM");
           	stylesheetDoc.async = false;
           	stylesheetDoc.loadXML(styleSheet);

           	theDocument = new ActiveXObject("Microsoft.XMLDOM");
           	theDocument.async = false;
           	theDocument.loadXML(rawFeed);

             	destinationDiv = document.getElementById("feed");
                destinationDiv.innerHTML = theDocument.transformNode(stylesheetDoc);

		feedLoaded = false;
		rawFeed = null;

         }

      }

</script>

</head>
<body>

<table width="100%" border="0">
<tr>
   <td id="main" width="200" valign="top"><h3>Main categories</h3>

<span onclick="getSubcategory(1)">Arts</span> (608)</br />
<span onclick="getSubcategory(2)">Business</span> (152)</br />
<span onclick="getSubcategory(3)">Comics</span> (21)</br />

<span onclick="getSubcategory(4)">Computers</span> (202)</br />
<span onclick="getSubcategory(5)">Games</span> (29)</br />
<span onclick="getSubcategory(6)">Health</span> (35)</br />

<span onclick="getSubcategory(7)">Home</span> (3)</br />
<span onclick="getSubcategory(8)">News</span> (66)</br />
<span onclick="getSubcategory(9)">Recreation</span> (21)



</td>
   <td width="200" valign="top"><h3>Sub categories</h3>

      <div id="sub"></div>

   </td>

   <td rowspan="2" valign="top"><div id="status"></div>
         <div id="feed"></div></td>
</tr>
<tr>
   <td colspan="2"><h3>Feeds</h3>

       <div id="feedlist"></div>

   </td>
</tr>
</table>

</body>
</html>

In this case, we can use the same exported function, x_proxy, but send the results to two different callback functions. Each one checks to see if the other has finished yet -- remember, were working asynchronously here -- and if so, performs the transformation and displays the results.

And we didn't have to touch the XMLHttpRequest object once.

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