hello guys?
i was recently studying how ajax work, problem is i followed some codes on the net and check if they work..they work on the site,but the time i tested those codes it wont work anymore..any ideas?ive tested js and it works on my browser...

<script type="text/javascript">
function loadXMLDoc()
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  if (xmlhttp.readyState==4 && xmlhttp.status==200)

<div id="myDiv"><h2>Let AJAX change this text</h2></div>
<button type="button" onclick="loadXMLDoc()">Change Content</button>


btw the code above was gotten from a tutorial site..
i really wna learn ajax but first i need this to get running..any1 generous enough to help me..thnks