JS倒计时器一只

 1 window.onload = function(){
 2     var uS = 604800;  //后台提供 : 秒
 3     var day=hour=minute=second=0, timer;
 4     var demo = document.getElementById("demo");
 5     //秒数转为 日:时:分:秒
 6     uS==0 || (uS<86400||(day=Math.floor(uS/86400), uS=uS%86400)) 
 7         && uS==0 || (uS<3600||(hour=Math.floor(uS/3600), uS=uS%3600)) 
 8         && uS==0 || (uS<60||(minute=Math.floor(uS/60), uS=uS%60)) 
 9         && uS==0 || (second=uS);
10     //计时器一只
11     timer = setInterval(function(){
12         demo.innerHTML= "还剩 "+day+"天"+hour+"时"+minute+"分"+second+"秒";
13         second!=0 ? second-- : 
14             (second=59, minute!=0 ? minute-- : 
15                 (minute=59, hour!=0 ? hour-- : 
16                     (hour=23, day!=0 ? day-- : 
17                         (hour=minute=second=0, clearInterval(timer)))));
18     },1000);
19 }

1 <div id="demo"></div>