js 加减乘除以及四舍五入 新写法

1 四舍五入

eg: (1.23).round() = 1.2

(1.2456).round(3) = 1.246

Number.prototype.round = function (count) {

    var res = ;

    var val = this.toString();

    var num = parseInt(count || );

    var dataArr = val.split('.');

    var arr1 = dataArr[] || "";

    var arr2 = dataArr[] || "";

    var newArr2 = arr2;

    if (arr2.length > num) {

      var lastNum = arr2.substring(num, num + );

      if (parseInt(lastNum) >= ) {

        newArr2 = parseInt(newArr2.substring(, num)) + ;

        newArr2 = newArr2.toString();

        if(newArr2.length<num){

          for(var i =; i< (num - newArr2.length); i ++){

            newArr2 = "" + newArr2;

          }

        }

        else if (newArr2.length > num) {

            arr1 = (parseInt(arr1) + ).toString();

            newArr2 = newArr2.substring(, );

        }

      }

    }

    val = parseFloat(arr1 + '.' + newArr2);

    res = parseFloat(val.toFixed(num));

    return res;

  }

2 加减乘除

eg: (1).plus(2) = 3

if (!Number.prototype.plus) { //'+'

    Number.prototype.plus = function (addend) {

        var arg1 = this,

            arg2 = addend;

        var r1,

            r2,

            m,

            num1,

            num2;

        try {

            r1 = arg1.toString().split(".")[].length;

        } catch (e) {

            r1 =

        }

        try {

            r2 = arg2.toString().split(".")[].length;

        } catch (e) {

            r2 =

        }

        m = Math.pow(, Math.max(r1, r2));

        num1 = r1 ==  ? parseInt(arg1 * m) : (parseInt(`${arg1.toString().replace('.', '')}`) * m / (Math.pow(, r1)));

        num2 = r2 ==  ? parseInt(arg2 * m) : (parseInt(`${arg2.toString().replace('.', '')}`) * m / (Math.pow(, r2)));

        return (num1 + num2) / m;

    }

}

if (!Number.prototype.minus) { //'-'

    Number.prototype.minus = function (Subtraction) {

        var arg1 = this,

            arg2 = Subtraction;

        var r1,

            r2,

            m,

            n,

            num1,

            num2;

        try {

            r1 = arg1.toString().split(".")[].length

        } catch (e) {

            r1 =

        }

        try {

            r2 = arg2.toString().split(".")[].length

        } catch (e) {

            r2 =

        }

        m = Math.pow(, Math.max(r1, r2));

        n = (r1 >= r2) ? r1 : r2;

        num1 = r1 ==  ? parseInt(arg1 * m) : (parseInt(`${arg1.toString().replace('.', '')}`) * m / (Math.pow(, r1)));

        num2 = r2 ==  ? parseInt(arg2 * m) : (parseInt(`${arg2.toString().replace('.', '')}`) * m / (Math.pow(, r2)));

        return parseFloat(((num1 - num2) / m).toFixed(n));

    }

}

if (!Number.prototype.multiply) { //'*'

    Number.prototype.multiply = function (multiple) {

        var arg1 = this,

            arg2 = multiple;

        var m = ,

            s1 = arg1.toString(),

            s2 = arg2.toString();

        try {

            m += s1.split(".")[].length

        } catch (e) { }

        try {

            m += s2.split(".")[].length

        } catch (e) { }

        return Number(s1.replace(".", "")) * Number(s2.replace(".", "")) / Math.pow(, m)

    }

    if (!Number.prototype.devide) { //'/'

        Number.prototype.devide = function (divisor) {

            var arg1 = this,

                arg2 = divisor;

            var t1 = ,

                t2 = ,

                r1,

                r2;

            try {

                t1 = arg1.toString().split(".")[].length

            } catch (e) { }

            try {

                t2 = arg2.toString().split(".")[].length

            } catch (e) { }

            r1 = Number(arg1.toString().replace(".", ""))

            r2 = Number(arg2.toString().replace(".", ""))

            return (r1 / r2).multiply(Math.pow(, t2 - t1));

        }

    }

}