jquery 倒计时效果实现秒杀思路

<script type="text/javascript">
$(function(){
countDown("2015/9/8 11:11:59","#colockbox1");
});
function countDown(time,id){
var day_elem = $(id).find('.day');
var hour_elem = $(id).find('.hour');
var minute_elem = $(id).find('.minute');
var second_elem = $(id).find('.second');

//if(typeof end_time == "string")
var end_time = new Date(time).getTime(),//月份是实际月份-1
sys_second = (end_time-new Date().getTime())/1000;
var timer = setInterval(function(){
if (sys_second > 1) {
sys_second -= 1;
var day = Math.floor((sys_second / 3600) / 24);
var hour = Math.floor((sys_second / 3600) % 24);
var minute = Math.floor((sys_second / 60) % 60);
var second = Math.floor(sys_second % 60);
day_elem && $(day_elem).text(day);//计算天
$(hour_elem).text(hour<10?"0"+hour:hour);//计算小时
$(minute_elem).text(minute<10?"0"+minute:minute);//计算分钟
$(second_elem).text(second<10?"0"+second:second);//计算秒杀
} else {
clearInterval(timer);
}
}, 1000);
}
</script>

<div class="colockbox" id="colockbox1">
<span class="day">00</span>
<span class="hour">00</span>
<span class="minute">00</span>
<span class="second">00</span>
</div>