Math functions suitable for monetary calculations

basic-math.js

/**
 * Basic Arithmetic
 */

const bind = Function.prototype.bind,
      liberate = bind.bind(Function.prototype.call),
      reduce   = liberate(Array.prototype.reduce),
      slice    = liberate(Array.prototype.slice);

function multiplier(x) {

    const parts = x.toString().split('.');

    if (parts.length < 2) {
        return 1;
    }

    return Math.pow(10, parts[1].length);
}

function correctionFactor() {

    return reduce(arguments, function (prev, next) {

        const mp = multiplier(prev),
              mn = multiplier(next);

        return mp > mn ? mp : mn;

    }, -Infinity);
}

export function add() {

    var corrFactor = correctionFactor.apply(null, arguments);

    function cback(accum, curr, currI, O) {
        return accum + corrFactor * curr;
    }

    return reduce(arguments, cback, 0) / corrFactor;
}

export function sub() {

    var corrFactor = correctionFactor.apply(null, arguments),
        first      = arguments[0];

    function cback(accum, curr, currI, O) {
        return accum - corrFactor * curr;
    }

    delete arguments[0];

    return reduce(arguments, 
            cback, first * corrFactor) / corrFactor;
}

export function mul() {

    function cback(accum, curr, currI, O) {

        var corrFactor = correctionFactor(accum, curr);

        return (accum * corrFactor) * (curr * corrFactor) /
            (corrFactor * corrFactor);
    }

    return reduce(arguments, cback, 1);
}

export function div() {

    function cback(accum, curr, currI, O) {

        var corrFactor = correctionFactor(accum, curr);

        return (accum * corrFactor) / (curr * corrFactor);
    }

    return reduce(arguments, cback);
}

sinful-math.js

// Taken from https://github.com/guipn/sinful.js
void function (bless) {

    'use strict';

    var bind     = Function.prototype.bind,
        liberate = bind.bind(Function.prototype.call),
        reduce   = liberate(Array.prototype.reduce),
        slice    = liberate(Array.prototype.slice);


    bless = bless || function (thing, name, content) {
        
        if (typeof thing[name] !== 'undefined') {
            throw new Error('Sinful: ' + name + ' is already defined.');
        }

        thing[name] = content;
    };

    function multiplier(x) {

        var parts = x.toString().split('.');

        if (parts.length < 2) {
            return 1;
        }

        return Math.pow(10, parts[1].length);
    }

    function correctionFactor() {

        return reduce(arguments, function (prev, next) {

            var mp = multiplier(prev),
                mn = multiplier(next);

        return mp > mn ? mp : mn;

        }, -Infinity);

    }

    [

        [Math, 'add', function () {

            var corrFactor = correctionFactor.apply(null, arguments);

            function cback(accum, curr, currI, O) {
                return accum + corrFactor * curr;
            }

            return reduce(arguments, cback, 0) / corrFactor;
        }],

        [Math, 'sub', function () {

            var corrFactor = correctionFactor.apply(null, arguments),
                first      = arguments[0];

            function cback(accum, curr, currI, O) {
                return accum - corrFactor * curr;
            }

            delete arguments[0];

            return reduce(arguments, 
                    cback, first * corrFactor) / corrFactor;
        }],

        [Math, 'mul', function () {

            function cback(accum, curr, currI, O) {

                var corrFactor = correctionFactor(accum, curr);

                return (accum * corrFactor) * (curr * corrFactor) /
                    (corrFactor * corrFactor);
            }

            return reduce(arguments, cback, 1);
        }],

        [Math, 'div', function () {

            function cback(accum, curr, currI, O) {

                var corrFactor = correctionFactor(accum, curr);

                return (accum * corrFactor) / (curr * corrFactor);
            }

            return reduce(arguments, cback);
        }],


    ].forEach(function (blessing) {
        bless(blessing.shift(), blessing.shift(), blessing.shift());
    });
}();

I have removed the wrapping code and the Math prototype changes from the original sinful.js code.

The result is at basic-math.js file.