<!DOCTYPE html>

<html>
    <head>
        <script>

            // toggles visibility of greeting
            function blink()
            {
                var div = document.getElementById('greeting');
                if (div.style.visibility == 'hidden')
                {
                    div.style.visibility = 'visible';
                }
                else
                {
                    div.style.visibility = 'hidden';
                }
            }

            // blink every 500ms
            window.setInterval(blink, 500);

        </script>
        <style>

            #greeting
            {
                font-size: 96pt;
                margin: 240px;
                text-align: center;
            }

        </style>
        <title>blink</title>
    </head>
    <body>
        <div id="greeting">
            hello, world
        </div>
    </body>
</html>