สวัสดีครับ คือผมรบกวนถาม เกี่ยวกับ AJAX Real Time นิดนึงครับ

function realtimeCustomer(cusID){
	createXMLHttpRequest();
	xhr.open("GET", "select.php?cusID="+cusID, true);
	xhr.send(null);
	xhr.onreadystatechange = function(){
		if(xhr.readyState == 4){
			if(xhr.status == 200){
				document.getElementById("resultCustomer").innerHTML=xhr.responseText;
			}else{
				document.getElementById("resultCustomer").innerHTML=xhr.statusText;
			}
		}
	}
}
function onloadCustomer(){
	realtimeCustomer("cus_id");
	setTimeout("doLoop()", 500);
}
function doLoop(){
	onloadCustomer();
}

function realtimeCustomer(cusID){
	createXMLHttpRequest();
	xhr.open("GET", "customer_select.php?cusID="+cusID, true);
	xhr.send(null);
	xhr.onreadystatechange = function(){
		if(xhr.readyState == 4){
			if(xhr.status == 200){
				document.getElementById("resultCustomer").innerHTML=xhr.responseText;
			}else{
				document.getElementById("resultCustomer").innerHTML=xhr.statusText;
			}
		}
	}
}
function onloadCustomer(){
	realtimeCustomer("cus_id");
	setTimeout("doLoop()", 500);
}
function doLoop(){
	onloadCustomer();
}

<?PHP
	include("connect.php");
	echo "Load Time : ".date("Y-m-d H:i:s")."<br />";
	$cusID=$_REQUEST["cusID"];
	$strSQL="SELECT * FROM tbl_customer ORDER BY $cusID DESC";
	$objQuery=mysql_query($strSQL) or die ("Error Query [".$strSQL."]");
	$num=mysql_num_rows($objQuery);
	if($num > 0){
?>