Hỏi 1 chút về jquery và ajax làm comment giống FB

/***************************/
//@Author: Adrian "yEnS" Mato Gondelle & Ivan Guardado Castro
//@website: www.yensdesign.com
//@email: yensamg@gmail.com
//@license: Feel free to use it, but keep this credits please!					
/***************************/

$(document).ready(function(){
	//global vars
	var inputUser = $("#nick");
	var inputMessage = $("#message");
	var loading = $("#loading");
	var messageList = $(".content > ul");
	
	//functions
	function updateShoutbox(){
		//just for the fade effect
		messageList.hide();
		loading.fadeIn();
		//send the post to shoutbox.php
		$.ajax({
			type: "POST", url: "shoutbox.php", data: "action=update",
			complete: function(data){
				loading.fadeOut();
				// lay du lieu xuat ra tu shoutbox.php ghep vap messageList
				messageList.html(data.responseText);
				messageList.fadeIn(2000);
			}
		});
	}
	//check if all fields are filled
	function checkForm(){
		if(inputUser.attr("value") && inputMessage.attr("value"))
			return true;
		else
			return false;
	}
	
	//Load for the first time the shoutbox data
	updateShoutbox();
	
	//on submit event
	$("#form").submit(function(){
		if(checkForm()){
			var nick = inputUser.attr("value");
			var message = inputMessage.attr("value");
			//we deactivate submit button while sending
			$("#send").attr({ disabled:true, value:"Sending..." });
			$("#send").blur();
			//send the post to shoutbox.php
			$.ajax({
				type: "POST", url: "shoutbox.php", data: "action=insert&nick=" + nick + "&message=" + message,
				complete: function(data){
					messageList.html(data.responseText);
					updateShoutbox();
					//reactivate the send button
					$("#send").attr({ disabled:false, value:"Shout it!" });
				}
			 });
		}
		else alert("Please fill all fields!");
		//we prevent the refresh of the page after submitting the form
		return false;
	});
	/*$(".delete").click(function(){
		//var id = $(this).val("id");
		// lay gia tri id co trong the a
		var id = $(this).attr('id');
		$.ajax({
			type: "POST", url: "shoutbox.php", data: "action=delete&id=" + id,
			complete: function(){
				updateShoutbox();
			}
		});
	});*/
});

function delete(id) {
	$.ajax({
		type: "POST", 
		url: "shoutbox.php", 
		data: "action=delete&id=" + id,
		success: function(){
			updateShoutbox();
		}
	});
}

if(!$_POST['action']){
	//We are redirecting people to our shoutbox page if they try to enter in our shoutbox.php
	header ("Location: index.html"); 
}
else{
	$link = connect(HOST, USER, PASSWORD);
	switch($_POST['action']){
		case "update":
			$res = getContent($link, 20);
			while($row = mysql_fetch_array($res)){
				$result .= "<li><strong>".$row['user']."</strong><img src=\"css/images/bullet.gif\" alt=\"-\" />".$row['message'].
				" <span class=\"date\">".$row['date']."</span>".
				"<span class=\"del\"><a href=\"#\" onclick=\"delete('{$row['id']}')\" class=\"delete\" id=".$row['id'].">.Delete.</a></span></li>";
			}
			echo $result;
			break;
		case "insert":
			echo insertMessage($_POST['nick'], $_POST['message']);
			break;
		case "delete":
			deleteMessage($_POST['id']);
			break;
	}
	mysql_close($link);
}

function deleteMessage($id){
	$res = @mysql_query("DELETE FROM shoutbox WHERE id={$id}");
}