ajax help plz

Here's my code

var xmlhttp

function addThis(str, add, sid)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
  {
  alert ("Your browser does not support XMLHTTP!");
  return;
  }
var url="/myscript.php";
url=url+"?id="+str;
url=url+"&action="+add;
url=url+"&sid="+sid;
xmlhttp.onreadystatechange=myStateChanged;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
  {
  // code for IE7+, Firefox, Chrome, Opera, Safari
  return new XMLHttpRequest();
  }
if (window.ActiveXObject)
  {
  // code for IE6, IE5
  return new ActiveXObject("Microsoft.XMLHTTP");
  }
return null;
}

function myStateChanged(tagname)
{
if (xmlhttp.readyState==4)
  {
   document.getElementById("comparebox").innerHTML=xmlhttp.responseText;
  document.getElementById(tagname).innerHTML=xmlhttp.responseText;
  }
}

Code (markup):

This works just fine until i change the:
xmlhttp.onreadystatechange=myStateChanged;
to
xmlhttp.onreadystatechange=myStateChanged(str);

I need to pass the variable str to the function myStateChanged so that it will find and change the content of the tag in my page.. but as soon as i add the "(str)" after the function's name it simply stops working

Whats wrong with this ?

 

try this one,