第二节 时钟表

1. 时钟表

思路：
1. 获取系统时间
2. gethours
   getMinutes
   getSeconds
3. 显示系统时间
   字符串连接
   小于10补零
4. 使用定时器setInterval()

<p id="p"></p>
    <script>
  setInterval(function(){
     var oDate=new Date();
     var hour=oDate.getHours();
     var minute=oDate.getMinutes();
     var seconds=oDate.getSeconds()
     function transform(params){
        return params=params<10?"0"+params:params;
     }
     hour=transform(hour)
     minute=transform(minute)
     seconds=transform(seconds)
     var sum=hour+":"+ minute+":"+seconds;
     var p=document.getElementById("p")
     p.innerHTML=sum;
    },1000)
    </script>

2. 倒计时

 <p id="p"></p>
    <script>
        /* 2019-09-19 09:00:00  */
        setInterval(function () {
            var oDate = new Date();
            var playTime = new Date("2019-09-19 09:00:00").getTime()
            var mill = oDate.getTime();
            var gapTime = playTime - mill;
            var seconds = Math.floor(gapTime / 1000);
            var hours = Math.floor(seconds / 3600)
            seconds = seconds % 3600;
            var minutes = Math.floor(seconds / 60)
            seconds = seconds % 60;
            function transform(params) {
                return params < 10 ? "0" + params : params;
            }
            var sum = transform(hours) + ":" + transform(minutes) + ":" + transform(seconds);
            document.getElementById("p").innerHTML = sum;
        },1000)
    </script>