1.Math

• Math.ceil()
• Math.floor()
• Math.round()
• Math.random() //返回一个随机数
• Math.max()

• Math.min

  console.log(Math.random()*100)  /* 0<=num<1 */  /* 0<num<0.999 */
  /* 1-100之间的随机数   1<=num<=100 */
  console.log(Math.floor(Math.random()*100)+1)

  2.Date

• //获取当前时间

• var oDate = new Date();
• var year = oDate.getFullYear();
• var month = oDate.getMonth();
• var date = oDate.getDate();
• var hour = oDate.getHours();
• var minute = oDate.getMinutes();
• var second = oDate.getSeconds();
• var mill = oDate.getTime();
• //月份从0开始
• var month = oDate.getMonth()+1;
• //星期从0开始，0表示星期天
• //0,1,2,3,4,5,6
• var day = oDate.getDay();

  3.实例

  3-1数码时钟

<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>

3-2定时器

 <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>

3-3间隔符转换

<script>
        var str = "2019/09/17 03:27:10";
        /* 2019-09-17 03/27/10 */
        var arr = str.split(" ")
        var day = arr[0].split('/').join("-");
        var time = arr[1].split(":").join("/");
        var sum = day+" "+time;
        console.log(sum)
    </script>