js实现指定时间倒计时时间效果

指定时间倒计时
div页

离2020还剩下
	

js页

 function autotime(){	
	 	var timenow=new Date();
		var time2020=new Date(2019,0,0,0,0,0);//指定时间
		var cz=time2020.getTime()-timenow.getTime();
		var day=parseInt(cz/(24*60*60*1000));
		  cz=cz%(24*60*60*1000);
		  hours=parseInt(cz/(60*60*1000));
		 cz=cz%(60*60*1000);
		 minute=parseInt(cz/(60*1000));
	     cz=cz%(60*1000);
		 var second=parseInt(cz/(1000));

		 var span=document.getElementById('a').getElementsByTagName('span');
		 span[0].innerHTML=day+"天";
		 span[1].innerHTML=hours+"时";
		 span[2].innerHTML=minute+"分";
		 span[3].innerHTML=second+"秒";
		  if(second<=-1)//如果溢出就为0并清除定时器
		 {
		 	span[0].innerHTML=0+"天";
		 span[1].innerHTML=0+"时";
		 span[2].innerHTML=0+"分";
		 span[3].innerHTML=0+"秒";
		 	clearInterval(time);
		 }
		}
	
		var time=setInterval(autotime,1000);
		time();