ex

1.倒计时

        function handleTime(value) {
            if (value < 10) {
                return "0" + value;
            }
            return "" + value;
        }
        function showTime() {
            var app = document.getElementById("app")
            var endTime = "2020-12-01 16:50:00";
            endTime = new Date(endTime).getTime();
            var nowTime = new Date().getTime();
            var gapTime = endTime - nowTime;
            // console.log(gapTime)
            var seconds = Math.floor(gapTime / 1000)
            // console.log(seconds)
            var hour =handleTime(Math.floor(seconds / 3600)) 
            // console.log(hour);
            seconds = seconds % 3600;
            var minute = handleTime(Math.floor(seconds / 60)) 
            // console.log(minute)
            seconds = handleTime(seconds % 60) ;
            // console.log(seconds);
            var sum=hour+":"+minute+":"+seconds;
            app.innerHTML=sum;
            setTimeout(function(){
                showTime()
            },1000)
        }
        showTime();

2.动态时钟

<div id="app">
        <img src="images/0.png" alt="">
        <img src="images/0.png" alt="">
        <span>:</span>
        <img src="images/0.png" alt="">
        <img src="images/0.png" alt="">
        <span>:</span>
        <img src="images/0.png" alt="">
        <img src="images/0.png" alt="">
    </div>

        function handleTime(value) {
            if (value < 10) {
                return "0" + value;
            }
            return "" + value;
        }
        function showTime() {
            var imgs=document.querySelectorAll("#app img")
           var d=new Date();
           var hour=handleTime(d.getHours());
           var minute=handleTime(d.getMinutes());
           var second=handleTime(d.getSeconds());
           var sum=hour+minute+second;
           for(i=0;i<imgs.length;i++){
               imgs[i].src="images/"+sum[i]+".png";
           }
            setTimeout(function(){
                showTime()
            },1000)
        }
        showTime();