JSFiddle - React, Tailwind, and code Playground

HTML

<script type="text/javascript">
    var timer, time = 0, start_time = 0;
    function startstoptimer() {
        if (timer) {
            time += new Date().getTime() - start_time;
            start_time = 0;
            clearInterval(timer);
            timer = null;
        } else {
            start_time = new Date().getTime();
            timer = setInterval(function () {
                document.d.d2.value = time + new Date().getTime() - start_time;
            }, 10);
        }
    }
    function resettimer() {
        time = 0;
        start_time = new Date().getTime();
        document.d.d2.value = "0";
    }
    </script>

    <form name="d">
        <input type="text" size="8" name="d2"/>
        <input type="button" value="Start/Stop" onclick="startstoptimer()"/>
        <input type="reset" onclick="resettimer()" />
    </form>