OpenJS > Articles > AHAH(Asynchronous HTML over HTTP)

AHAH(Asynchronous HTML over HTTP)

AHAH or Asynchronous HTML over HTTP is a much simpler version of AJAX. Using AHAH approach in JavaScript you can display external XHTML pages inside your HTML page. The beauty of the script is that it is very simple - the underling code is just twenty lines!

The difference between AJAX and AHAH is the return data fomat. AJAX will load an XML file - then the developer will have to make the code that will parse the XML, extract the data and then display the results. In AHAH the approach is much simpler - the data to be fetched is XHTML - the code just has to fetch it - as the browser is already equipped to handle HTML and will display the result with no further help from the developer.

Use

For example, lets say we need to create a page with tabs - each tab will put some content in the main area - but the full thing must be dynamic - linking to another page won't do. The code of the main page will be...

<ul id="tabs">
 <li><a href="javascript:load('javascript.html');">JavaScript</a></li>

 <li><a href="javascript:load('ahah.html');">AHAH</a></li>
 <li><a href="javascript:load('ajax.html');">AJAX</a></li>
</ul>

<div id="content"></div>

The point of our exercise will be to load the contents of the javascript.html in to the div with the id 'content'. In the JavaScript section of the file we will declare the 'load' function...

<script language="javascript" type="text/javascript" src="ahah.js"></script>
<script language="javascript" type="text/javascript">
//Calls the library function 'ahah' - defined in 'ahah.js' file.
function load(filename) {
	ahah(filename,"content");
}
</script>

The code of the ahah.js file as given below...

function ahah(url, target) {
  document.getElementById(target).innerHTML = ' Fetching data...';
  if (window.XMLHttpRequest) {
    req = new XMLHttpRequest();
  } else if (window.ActiveXObject) {
    req = new ActiveXObject("Microsoft.XMLHTTP");
  }
  if (req != undefined) {
    req.onreadystatechange = function() {ahahDone(url, target);};
    req.open("GET", url, true);
    req.send("");
  }
}  

function ahahDone(url, target) {
  if (req.readyState == 4) { // only if req is "loaded"
    if (req.status == 200) { // only if "OK"
      document.getElementById(target).innerHTML = req.responseText;
    } else {
      document.getElementById(target).innerHTML=" AHAH Error:\n"+ req.status + "\n" +req.statusText;
    }
  }
}

Now the only file left is the three content files - javascript.html, ahah.html and ajax.html. The important thing to remember about this is that you should not include the standard HTML stuff like <html><body> etc. in this page - just the content with all the HTML formatting - I am just providing the code for just the file javascript.html here - remember that this is the whole file - nothing other than the shown data must be in that file.

<h1>JavaScript</h1>

<p><b><u>JavaScript</u></b> is Netscape's cross-platform, object-based scripting 
language for client and server applications. It has dominated the world of internet scripting languages 
for a long time now. With the arrival of new programming methods like <a class="tooltip" 
title="AJAX : Asynchronous JavaScript and XML" href="http://en.wikipedia.com/wiki/AJAX">AJAX</a>, 
it is much more popular now than ever before.</p>

<p>See the wikipedia article on <a  href="http://en.wikipedia.com/wiki/JavaScript">JavaScript</a>

for more info on this language.</p>

Use you imagination to create the other two files. Now open the page on a browser to see the magic. See the live example...