JS倒计时

<script type="text/javascript">
    var timeout;
    $(function () {
        timeout = setInterval(showsykssj, 1000);
    })

    function showsykssj() {
        /*显示剩余考试时间*/
        var hour = 12;   //结束时间
        var minite = 0;
        var second = 0;
        var date1 = new Date(1986, 1, 22, hour, minite, second);
        var date2 = new Date(1986, 1, 22, new Date().getHours(), new Date().getMinutes(), new Date().getSeconds());
        var nDiff = date1 - date2;
        var nHour, nMini, nSecond;

        nHour = parseInt(nDiff / 3600000);
        nMini = parseInt(nDiff % 3600000 / 60000);
        nSecond = parseInt(nDiff % 60000 / 1000);
        if (nMini == 0 && nSecond == 0) {
            alert("考试时间到，系统自动交卷。");
            clearInterval(timeout);
        }
        else {
            document.getElementById("sykssj").innerHTML = "距离" + hour + "点" + minite + "分" + second + "秒还有：" + nHour + "小时" + nMini + "分" + nSecond + "秒";
        }
    }
    </script>