倒计时效果

/**
* Created by liweiliang on 2017/7/18 QQ:406320591.
*/
function tow(n) {
    return n >= 0 && n < 10 ? '0' + n : '' + n;
}
function countDown(){
var end = +new Date("2017-07-25 00:00:00"),//获取指定日期对象
start = +new Date(),//获取现在日期对象
second = Math.floor((end - start)/1000);//未来时间距离现在的秒数
day = Math.floor( second/(24*60*60) );//整数部分代表的是天；一天有24*60*60=86400秒 ；
var t1 =second - (day*24*60*60);
hour = Math.floor( t1/(60*60) );//整数部分代表小时；
var t2 = t1 - hour*60*60;
min = Math.floor( t2/60 );
sec =t2%60;
seckill = '<span class="seckill-time">' + tow(day) + '</span><span class="delimiter">:</span><span class="seckill-time">' + tow(hour) + '</span><span class="delimiter">:</span><span class="seckill-time">' + tow(min) + '</span><span class="delimiter">:</span><span class="seckill-time">' +tow(sec) + '</span>';
document.getElementById("seckill").innerHTML=seckill;
}
window.onload = function(){
    countDown();
    setInterval(countDown,1000);
}