Math-Extends 1.0.0 @class MathExtends @constructor decimal 全局保留位数 @author BaoQiang.Xu @api npm install math-extends -d const MathExtends = require('math-extends') const math = new MathExtends(2) math.$add(num1, num2, ?decimal) 加 math.$sub(num1, num2, ?decimal) 减 math.$mul(num1, num2, ?decimal) 乘 math.$dev(num1, num2, ?decimal) 除