why does not the page stays at wher eit is when i refresh the page even when i am using the session correctly.

config.php //database connection is in it and session is started.
<?php
	session_start();
	$db_host="localhost";
	$db_name="session_cms_ajax";
	$username="root";
	$password="";
	$db_con=mysql_connect($db_host,$username,$password) or die("connection not build".mysql_error());
	$db=mysql_select_db($db_name) or die("database not build".mysql_error());
?>
 
index.php   //login form is shown
<?php include('config.php'); ?>
<script type="text/javascript" language="javascript" src="javascript/login.js"></script>
 
<div id="login" style="background-color:#CCCCCC;"></div> 
<br />
<?php if(!isset($_SESSION['loggedin'])){
?>
<div id="loginform">
<form action="javascript:login()" method="post">
<table border="1" bgcolor="#CCCCCC">
	<tr><td colspan="2" align="center"><h3>Login Form</h3></td></tr>
	<tr><td>Username</td><td><input name="username" type="text" id="username" /></td></tr>
	<tr><td>Password</td><td><input name="password" type="password" id="password" /></td></tr>
	<tr><td>&nbsp;</td><td><input type="button" name="login" value="Login" onclick="mylogin();" />
	<input type="button" name="logout" value="Logout" onclick="mylogout();" /></td>
	</tr>
</table>
</form>
</div>
<?php }?>
<div id="dropdownlist"></div>
<div id="logout"></div>
 
//login.php
<?php 
include('config.php'); 
$username = $_GET['username'];
$password = $_GET['password'];
 
$sql = 'select count(*) as total from login where username="'. $username . '" and password = "' . $password . '"';
$query = mysql_query($sql);
$rec = mysql_fetch_assoc($query);
$num_rows = intval($rec['total']);
if( $num_rows > 0){
	$_SESSION['loggedin'] = 1 ;
	?> <div id="login"><a href="javascript:dropdownlist();"><h3><?php echo $username; ?></h3></a></div> <?php 
}
else{ echo "no"; }
?>
 
dropdownlist.php
<?php include('config.php'); 
if(isset($_SESSION['loggedin'])){
	echo $_SESSION['loggedin'];
	echo "i am in dropdownlist page. This is my private page.";
}
?>
 
logout.php
<?php
include('config.php');
session_destroy();
$_SESSION['loggedin'] = 0 ;
?>
 
login.js
function createObject() {
	var request_type;
	var browser = navigator.appName;
	if(browser == "Microsoft Internet Explorer"){
		request_type = new ActiveXObject("Microsoft.XMLHTTP");
	} else{
		request_type = new XMLHttpRequest();
	}
	return request_type;
}
var http = createObject();
 
function mylogin() {
	var username = encodeURI(document.getElementById('username').value);
	var password = encodeURI(document.getElementById('password').value);
	http.open('get', 'login.php?username='+username+'&password='+password);
	http.onreadystatechange = function(){
	 if(http.readyState == 4){
		var response = http.responseText;
		var res = response.replace(/^\s+|\s+$/, '');
		if(res == "no"){
				document.getElementById('login').innerHTML = 'Login Failed';
				document.getElementById('loginform').style.display = 'block';
		} else {
				document.getElementById('login').innerHTML = response;
				document.getElementById('loginform').style.display = 'none';
		}
	}
	}
	http.send(null);
}
 
function mylogout(){
	document.getElementById('loginform').style.display = 'none';
	http.open('get','logout.php', true); // here we are calling the respective page
	http.onreadystatechange = function(){
	if(http.readyState == 4){
		var response = http.responseText;
		//alert(response)
		document.getElementById('logout').innerHTML = response; // menu links
		}
	}
	http.send(null);		
}
 
function dropdownlist(){
	http.open('get','dropdownlist.php', true); // here we are calling the respective page
	http.onreadystatechange = function(){
	if(http.readyState == 4){
		var response = http.responseText;
		//alert(response)
		document.getElementById('dropdownlist').innerHTML = response; // menu links
		}
	}
	http.send(null);
}

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