ajax call from java script....

var custID = document.getElementById("customerID").value;
        var custName = document.getElementById("customerName").value;
        var left = (screen.width/2) - (650/2);
        var top = (screen.height/2) - (450/2);
        if((document.getElementById("customerID").value == "") && (document.getElementById("customerName").value == "")){
            alert("Please enter Customer ID or Customer Name to search.");
            document.getElementById("customerID").focus();
            return false;
        } else {       
            //window.open("FileDocumentServlet?eid=<%=FileDocumentEventNames.BUSINESS_FORMATION_SEARCH_CUST%>&customerID="+custID+"&customerName="+custName, "customerWindow",
            //"toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,copyhistory=no,width=850,height=430,top="+top+",left="+left);
            document.getElementById("button").click();
            var url = "FileDocumentServlet?eid=<%=FileDocumentEventNames.BUSINESS_FORMATION_SEARCH_CUST%>&customerID="+custID+"&customerName="+custName;
            if (window.XMLHttpRequest){// code for IE7+, Firefox, Chrome, Opera, Safari
                  xmlhttp=new XMLHttpRequest();
            } else {// code for IE6, IE5     
                  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
            }
            xmlhttp.onreadystatechange = function(){
              if(xmlhttp.readyState == 4 && xmlhttp.status == 200){ 
                 var customerResult = xmlhttp.responseText;
                    document.getElementById("popupContact").innerHTML = customerResult;                 
                    return true;
                 } else {
                     document.getElementById("popupContact").innerHTML = document.getElementById("loadingMessageId").innerHTML;
                 }
             }  
             xmlhttp.open("POST",url,true);
          xmlhttp.send();
                 
        }