js浮点运算0.1+0.2=0.3和日期格式化

//调用方法：Number.add(0.1, 0.2)
//Date.fmt(1596509653796 , "YYYY-MM-DD hh:mm:ss")

Object.prototype.addMethod = function (name, fn) {
    var old = this[name];
    this[name] = function () {
        var fncLen = fn.length,
            argLen = arguments.length;
        if (fncLen === argLen) {
            return fn.apply(this, arguments);
        } else if (typeof old === "function") {
            return old.apply(this, arguments);
        } else {
            throw new Error("no method with " + argLen + " param(s) defined!");
        }
    }
}

/*
* 核心方法，实现加减乘除运算，确保不丢失精度
* 思路：把小数放大为整数（乘），进行算术运算，再缩小为小数（除）
*
* @param a {number} 运算数1
* @param b {number} 运算数2
* @param op {string} 运算类型，有加减乘除（add/subtract/multiply/divide）
*
*/

var __number__ = {
    operation: function (a, b, op) {
        var o1 = __number__.toInteger(a || 0);
        var o2 = __number__.toInteger(b || 0);
        var n1 = o1.num;
        var n2 = o2.num;
        var t1 = o1.times;
        var t2 = o2.times;
        var max = t1 > t2 ? t1 : t2;
        var result = null;

        switch (op) {
            case 'add':
                if (t1 === t2) { // 两个小数位数相同
                    result = n1 + n2
                } else if (t1 > t2) { // o1 小数位 大于 o2
                    result = n1 + n2 * (t1 / t2)
                } else { // o1 小数位 小于 o2
                    result = n1 * (t2 / t1) + n2
                }
                return result / max;

            case 'subtract':
                if (t1 === t2) {
                    result = n1 - n2
                } else if (t1 > t2) {
                    result = n1 - n2 * (t1 / t2)
                } else {
                    result = n1 * (t2 / t1) - n2
                }
                return result / max;

            case 'multiply':
                result = (n1 * n2) / (t1 * t2);
                return result;

            case 'divide':
                result = (n1 / n2) * (t2 / t1);
                return result
        }
    },

    isInteger: function (obj) {
        return Math.floor(obj) === obj
    },

    /*
    * 将一个浮点数转成整数，返回整数和倍数。如 3.14 >> 314，倍数是 100
    * @param floatNum {number} 小数
    * @return {object}
    *  {times:100, num: 314}
    */

    toInteger: function (floatNum) {
        var ret = {
            times: 1,
            num: 0
        };

        if (__number__.isInteger(floatNum)) {
            ret.num = floatNum;
            return ret
        }

        var strfi = floatNum + '';
        var dotPos = strfi.indexOf('.');
        var len = strfi.substr(dotPos + 1).length;
        var times = Math.pow(10, len);
        var intNum = parseInt(floatNum * times + 0.5, 10);
        ret.times = times;
        ret.num = intNum;
        return ret
    },

    add: function (a, b) {
        return __number__.operation(a, b, 'add')
    },

    subtract: function (a, b) {
        return __number__.operation(a, b, 'subtract')
    },

    multiply: function (a, b) {
        return __number__.operation(a, b, 'multiply')
    },

    divide: function (a, b) {
        return __number__.operation(a, b, 'divide')
    }

}

Number.addMethod('add', __number__.add) // Number.add(0.1, 0.2)
Number.addMethod('subtract', __number__.subtract)
Number.addMethod('multiply', __number__.multiply)
Number.addMethod('divide', __number__.divide)

var __date__ = {
    /**
    *  fmt = "YYYY-MM-DD hh:mm:ss" => 2016-04-01 10:41:08
    *  fmt = "YY-MM-DD hh:mm:ss" => 16-04-01 10:41:08
    *  fmt = "Y-M-D hh:mm:ss" => 16-4-1 10:41:08
    *  fmt = "MM/DD<br>hh:mm" => 01/12<br>12:05
    **/

    fmt: function (timestamp, fmt) {
        if (typeof timestamp === 'string')
            timestamp = parseInt(timestamp, 10)
            
        const t = new Date(timestamp)
        var o = {
            "Y+": t.getFullYear(),
            "M+": t.getMonth() + 1,
            "D+": t.getDate(),
            "h+": t.getHours(),
            "m+": t.getMinutes(),
            "s+": t.getSeconds()
        };

        for (var k in o) {
            if (new RegExp("(" + k + ")").test(fmt)) {
                if (k == "Y+") fmt = fmt.replace(RegExp.$1, ("" + o[k]).substr(4 - RegExp.$1.length));
                else fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
            }
        }

        return fmt;
    },

    /**
    * 星期一：Monday（Mon.）
    * 星期二：Tuesday（Tues.）
    * 星期三：Wednesday（Wed.）
    * 星期四：Thursday（Thur./Thurs.）
    * 星期五：Friday（Fri.）
    * 星期六：Saturday（Sat.）
    * 星期日：Sunday（Sun.）
    **/

    get_week: function (timestamp, fmt) {
        if (typeof timestamp === 'string')
            timestamp = parseInt(timestamp, 10)
        const t = new Date(timestamp).getDay()

        if (fmt == 'zh') {
            fmt = ["星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"]
        } else if (fmt == 'en') {
            fmt = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
        } else if (fmt == 'zh-abbr') {
            fmt = ["日", "一", "二", "三", "四", "五", "六"]
        } else if (fmt == 'en-abbr') {
            fmt = ["Mon", "Tues", "Wed", "Thur", "Fri", "Sat", "Sun"]
        } else if (!Array.isArray(fmt)) {
            return t
        }

        return fmt[t];
    }
}

Date.addMethod('fmt', __date__.fmt)
Date.addMethod('get_week', __date__.get_week)