js实现倒计时

    <div id="date">
        倒计时还有<span id="span_dt_dt" class="numda"></span>

        <script language="JavaScript" type="text/javascript">

                                        function show_date_time() {
                                            window.setTimeout("show_date_time()", 1000);
                                            BirthDay = new Date("02/02/2011 06:00:00"); //这个日期是可以修改的 
                                            today = new Date();
                                            timeold = (BirthDay.getTime() - today.getTime());
                                            sectimeold = timeold / 1000
                                            secondsold = Math.floor(sectimeold);
                                            msPerDay = 24 * 60 * 60 * 1000
                                            e_daysold = timeold / msPerDay
                                            daysold = Math.floor(e_daysold);
                                            e_hrsold = (e_daysold - daysold) * 24;
                                            hrsold = Math.floor(e_hrsold);
                                            e_minsold = (e_hrsold - hrsold) * 60;
                                            minsold = Math.floor((e_hrsold - hrsold) * 60);
                                            seconds = Math.floor((e_minsold - minsold) * 60);
                                            span_dt_dt.innerHTML = "<b><align=center><font color=D70010>" + daysold + "" + "</font>";
                                        }
                                        show_date_time(); 
   

        </script>        天&nbsp;&nbsp;&nbsp;&nbsp;

    </div>