AJAX

 
 <script language="javascript">
  var xmlhttp;
  try
  {
    xmlhttp=new ActiveXObjt("Msxml2.XMLHTTP");
  }
  catch(e)
  {
    try
    {
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
     }
    catch(e)
     {
     xmlhttp=new XMLHttpRequest ();
     }
  }
  xmlhttp.onreadystatechange=function ()
    {
     if (xmlhttp.readyState==4)
       {
        if (xmlhttp.status==200)
        {
          var showHtml =xmlhttp.responseText;
          alert (showHtml);
        }
        else 
        { 
           alert(xmlhttp.readyState);
        }
       }
    } 
    xmlhttp.open("get","aa.html",true);
     xmlhttp.send(null);
 </script>