JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html dir="ltr">
    <body>
        <span id="raw">Raw</span><br />
        <span id="converted">Converted</span>

        <script type="text/javascript">
            var datum = "/Date(1224043200000-0600)/";

            function formatDate(value) {
                return new Date(value);
            }

            var RAW = document.getElementById("raw");
            var CONVERTED = document.getElementById("converted");

            RAW.innerHTML = datum;
            var date = new Date(parseInt(datum.substr(6)));
            CONVERTED.innerHTML = formatDate(date);
        </script>
    </body>
</html>