TestPage.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>Multi window</title>
    <script src="https://code.jquery.com/jquery-1.12.4.min.js" type="text/javascript"></script>
    <script src="Duplicate.js"></script>
</head>
<body>
    This is test page,<br/><a href="TestPage.html" target="_blank">Click here</a> to open another window
    <script type="text/javascript">
        $(document).ready(function () {
            if (window.IsDuplicate()) {
                alert("this is duplicate window\n\n closing...");
                window.close();
            }
        });
    </script>
</body>
</html>