倒计时javascript

<script type="text/javascript">
 var serverTime = <?php echo time();?>  * 1000;
 var gotobuy=0,gotopay=0;
 var timeout=null;
 $(function(){ 
     var dateTime = new Date(); 
     var difference = dateTime.getTime() - serverTime;
      
      timeout = setInterval(function(){ 
       $(".endtime").each(function(){ 
         var obj = $(this); 
         var endTime = new Date(parseInt(obj.attr('value')) * 1000); 
         var nowTime = new Date(); 
         var nMS=endTime.getTime() - nowTime.getTime() + difference; 
         var myD=Math.floor(nMS/(1000 * 60 * 60 * 24)); //天 
         var myH=Math.floor(nMS/(1000*60*60)) % 24; //小时 
         var myM=Math.floor(nMS/(1000*60)) % 60; //分钟 
         var myS=Math.floor(nMS/1000) % 60; //秒 
         var myMS=Math.floor(nMS/100) % 10; //拆分秒 
         if(myD>= 0){
             var str = (myD>0?'<span>'+myD+'</span>天':'')+'<span>'+myH+'</span>小时<span>'+myM+'</span>分<span>'+myS+'</span>秒<span>'+myMS+'</span>';
            //显示倒计时
         }else{
　　　　　　//倒计时结束
            window.clearInterval(timeout);
            var str = '<span>0</span>小时<span>0</span>分<span>0</span>秒';
           
         }
         obj.html(str);
       }); 
     }, 100);

 });
</script>