javaScript实现一个倒计时功能

直接撸代码：

<div class="time">
        <span id="showTime"></span>
</div>
<script>
function countDown(time,id){
        var startTime = new Date();
        var endTime = new Date(time);
        var distance = endTime.getTime() - startTime.getTime();

        var day = 0;
        var hour = 0;
        var minute = 0;
        var second =0;

        if(distance>=0){
            day = Math.floor(distance/1000/60/60/24);
            hour = Math.floor(distance/1000/60/60%24);
            minute = Math.floor(distance/1000/60%60);
            second = Math.floor(distance/1000%60);
        }else{
            alert("倒计时活动已结束");
        }
        document.getElementById(id).innerHTML = day + "天" +  hour + "时" + minute + "分" + second + "秒";
    }
    // countDown('2019/07/25 19:15:00','showInterval');
    setInterval(function(){countDown('2019/07/26 12:00:00','showTime');},0);
<script>