jQuery怎样实现动态倒计时效果？

<script>
function show_time() {
    $(".count-down-block").each(function() {
        var endtime = '<?=$onsaletime?>';
        var time_start = new Date().getTime(); //设定当前时间
        var time_end = new Date(endtime).getTime(); //设定目标时间
        var time_distance = time_end - time_start;
        var timer;
        if (time_distance >= 0) {
            var int_day = Math.floor(time_distance / 86400000)
            time_distance -= int_day * 86400000;
            var int_hour = Math.floor(time_distance / 3600000)
            time_distance -= int_hour * 3600000;
            var int_minute = Math.floor(time_distance / 60000)
            time_distance -= int_minute * 60000;
            var int_second = Math.floor(time_distance / 1000)
            if (int_day < 10) {
                int_day = "0" + int_day;
            }
            if (int_hour < 10) {
                int_hour = "0" + int_hour;
            }
            if (int_minute < 10) {
                int_minute = "0" + int_minute;
            }
            if (int_second < 10) {
                int_second = "0" + int_second;
            }
            // $(this).html(int_day + "天" + int_hour + "时" + int_minute + "分" + int_second + "秒");
            $("span.count-down-time-box.day").text(int_day);
            $("span.count-down-time-box.hour").text(int_hour);
            $("span.count-down-time-box.minute").text(int_minute);
            $("span.count-down-time-box.second").text(int_second);

        }else{
            clearInterval(timer);
            $(this).css("display","none");
        }
    })
    timer = setTimeout("show_time()", 1000);
}
show_time();
</script>