สอบถามวิธี loading request Jquery ครับ ให้ขึ้น loading ก่อนแสดงผล

<script type="text/javascript">
function searchSubject()
{
	$.post("result_sub.php",{
		mySearch: $("#txtSearch").val()},
		function(msg){
			$("#myResult").html(msg);
		}
	);
}
</script>

<label for="txtSearch">ค้นหาจากรหัสวิชาหรือชื่อวิชา : </label>
    <input type="text" name="txtSearch" id="txtSearch" />
    <input type="button" name="btn_search" id="btn_search" value="ค้นหา" onclick="javascript:searchSubject();" />
</div>
<div class="cleaner_h5"></div>
<div id="loading" align="center"></div>
<span id="myResult"></span>

function searchSubject(){
	$.ajax({
		url: 'result_sub.php',
		data: {mySearch: $("#txtSearch").val()},
		type: 'post',
		success: function (response) {
			$("#myResult").html(response);
		}
	}).ajaxStart(function() {
		/* Stuff to do when an AJAX call is started and no other AJAX calls are in progress */;
	}).ajaxStop(function() {
		/* stuff to do when all AJAX calls have completed */;
	});
}

<div align="center">
	<label for="txtSearch">ค้นหาจากรหัสวิชาหรือชื่อวิชา : </label>
	<input type="text" name="txtSearch" id="txtSearch" />
	<input type="button" name="btn_search" id="btn_search" value="ค้นหา" onclick="javascript:searchSubject();" />
</div>
<div class="cleaner_h5"></div>
<div id="loading2" align="center"></div>
<span id="myResult"></span>

$(document).ready(function() {
	$('#btn_search').click(function(event) {
		var keyWord = $("#txtSearch").val();
		if(keyWord!=""){
			$.ajax({
				url:'result_sub.php',
				data:{ mySearch:keyWord },
				type:'post',
				success:function(msg){
					$("#myResult").html(msg);
				}
			});
		}
	});
}).ajaxStart(function(){
	$("#loading2").html('<div align="center"><img src="img/loading2.gif"></div>');
}).ajaxStop(function(){
	$("#loading2").hide();
});