- session_start: documentation ( source)
<?php
session_start();
$_SESSION['flag'] = 1;
?>
<html>
<head>
</head>
<body>
<!-- page content here -->
<?php if ($_SESSION['flag'] === 0): ?>
<script src="loggedIn.js"></script>
<?php else: ?>
<script src="loggedOut.js"></script>
<?php endif; ?>
</body>
</html>