//按天数倒计时 function _fresh(a){ a=$('.tim').attr('id'); var endtime=new Date("Dec 31, 2017 18:00:00");//这里设置预制时间 var nowtime = new Date(); var leftsecond=parseInt((endtime.getTime()-nowtime.getTime())/1000); if(leftsecond<0){leftsecond=0;} __d=parseInt(leftsecond/3600/24); __h=parseInt((leftsecond/3600)%24); __m=parseInt((leftsecond/60)%60); __s=parseInt(leftsecond%60); document.getElementById(a).innerHTML=__d+"天 "+__h+"小时"+__m+"分"+__s+"秒"; } _fresh(a); setInterval(_fresh,1000);
<span class="tim" id="timer_all"></span>