<html>
<head>
    <script type="text/javascript">
        window.onload = function() {
            document.getElementById('test').addEventListener('keypress', function(e) {
                out = document.getElementById('out');
                out.innerHTML = 'keyCode: ' + e.keyCode + ' (should be 13)';
                if (e.keyCode == 13)
                    out.style.background = '#6f6';
                else
                    out.style.background = '#f66';
            }, false);
            document.getElementById('test').focus()
        };
    </script>
</head>
<body>
    <p>Press the numpad Enter key while the input box below is focused:</p>
    <p><input type="text" id="test" /></p>
    <p id="out"></p>
</body>
</html>