一、效果图

 

 二、代码

    <h1>Countdown Clock</h1>
<div id="clockdiv">
  <div>
    <span class="days">00</span>
    <div class="smalltext">Days</div>
  </div>
  <div>
    <span class="hours">00</span>
    <div class="smalltext">Hours</div>
  </div>
  <div>
    <span class="minutes">00</span>
    <div class="smalltext">Minutes</div>
  </div>
  <div>
    <span class="seconds">00</span>
    <div class="smalltext">Seconds</div>
  </div>
</div>
<script type="text/javascript">
let ut = {};
const countDown = function(time, fn) {
    let maxtime = time - new Date().getTime(), //剩余秒
    timer = setInterval(function() {
        if (maxtime >= 0) {
            const dd = parseInt(maxtime / 60 / 60 / 24, 10), //计算剩余的天数  
            hh = (Array(2).join(0) + parseInt(maxtime / 60 / 60 % 24, 10)).slice(-2), //计算剩余的小时数  
            mm = (Array(2).join(0) + parseInt(maxtime / 60 % 60, 10)).slice(-2), //计算剩余的分钟数  
            ss = (Array(2).join(0) + parseInt(maxtime % 60, 10)).slice(-2); //计算剩余的秒数  

            fn({dd, hh, mm, ss});
            --maxtime;
        } else {
            clearInterval(timer)
            fn({})
        }
    }, 1000)
},
showtime = function(time) 
{
    const clock = document.getElementById("clockdiv"),
    daysSpan = clock.querySelector('.days'),
    hoursSpan = clock.querySelector('.hours'),
    minutesSpan = clock.querySelector('.minutes'),
    secondsSpan = clock.querySelector('.seconds');

    if(undefined === time.ss) {
        clock.innerHTML = '结束了';
        return false;
    }
    
    if(undefined === ut.dd || time.dd !== ut.dd) daysSpan.innerHTML = time.dd;
    if(undefined === ut.hh || time.hh !== ut.hh) hoursSpan.innerHTML = time.hh;
    if(undefined === ut.mm || time.mm !== ut.mm) minutesSpan.innerHTML = time.mm;
    secondsSpan.innerHTML = time.ss;
    ut = time;
};

countDown(new Date().getTime() + 60 * 60 * 24 * 10, showtime);
</script>

<style type="text/css">
body{
    text-align: center;
    background: #00ECB9;
    font-family: sans-serif;
    font-weight: 100;
}

h1{
    color: #396;
    font-weight: 100;
    font-size: 40px;
    margin: 40px 0px 20px;
}

#clockdiv{
    font-family: sans-serif;
    color: #fff;
    display: inline-block;
    font-weight: 100;
    text-align: center;
    font-size: 30px;
}

#clockdiv > div{
    padding: 10px;
    border-radius: 3px;
    background: #00BF96;
    display: inline-block;
}

#clockdiv div > span{
    padding: 15px;
    min-width: 48px;
    border-radius: 3px;
    background: #00816A;
    display: inline-block;
}

.smalltext{
    padding-top: 5px;
    font-size: 16px;
}
  </style>