The // comment tag enables comments to be placed between the // and the end of the line.
<html>
<head>
<title>A Simple Page</title>
<script language="javascript">
<!--
// The first alert is below
alert("An alert triggered by JavaScript!");
// Here is the second alert
alert("A second message appears!");
// -->
</script>
</head>
<body>
</body>
</html>