2.Math

Math.max()     取最大值
Math.min()     取最小值
Math.ceil()    向上取整
Math.floor()   向下取整
Math.round()   四舍五入
Math.random()  随机数
    <script>
        var num =13.45;
        console.log(Math.ceil(num))
        console.log(Math.floor(num))
        /* Math.round四舍五入取整 */
        console.log(Math.round(13.16))
        console.log(Math.max(4,5,6))
        console.log(Math.min(4,5,6))
        /* 0=<num<1*/
        console.log(Math.random())
    </script>