1.Math

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

var num = 12.26;
console.log(Math.ceil(num)); //13
console.log(Math.floor(num)); //12
console.log(Math.round(num)); //12
console.log(Math.random(num)); //随机数