7.1、math

math.max()     取最大值
math.min()     取最小值
math.ceil()    上取整
math.floor()   下取整
math.round()   四舍五入取整
math.random()  随机数 0<=num<1

var num = 12.66;
console.log(Math.ceil(num));   // 13
console.log(Math.floor(num));   //12
console.log(Math.round(num));   //13
console.log(Math.random());