how people do it

usualIQ = 120
workingHoursPerDay = 6

getWorkingDaysInMonth = (date) ->
    isWorkingDate = (date) ->
        day = date.getDay()
        return day isnt 0 and day isnt 6
    daysInMonth = new Date(date)
    daysInMonth.setMonth(daysInMonth.getMonth() + 1)
    daysInMonth.setDate(0)
    daysInMonth = date.getDate()

    days = 0

    while (days < daysInMonth)
        days++ if isWorkingDate(date)
        date.setDate(date.getDate() + 1)
    return days


class Money
    constructor: (@money=0) ->

    add: (money) ->
        @money += money

    valueOf: () ->
        return @money

    toString: () ->
        return @money


class Wallet extends Money


class Salary extends Money


class Bonus extends Money


class Human
    constructor: () ->

    hi: () ->
        throw new Error("doesn't implemented")


class Person extends Human
    constructor: (@name, @iq) ->

    isClever: () ->
        return @iq > usualIQ

    hi: () ->
        return "Hi, my name is #{@name}, my iq is #{@iq}"


class Employee extends Person
    constructor: (@name, @iq, @rate) ->

        @wallet = new Wallet()

    getMonthlyRate: () ->
        date = new Date()
        return getWorkingDaysInMonth(date) *  @rate * workingHoursPerDay

    pay: (salary) ->
        @wallet.add(salary)

    hi: () ->
        return 'Bip Bop...'


employee = new Employee('a', 121, 20)

console.log(employee.hi())
console.log(employee.isClever())
console.log(employee.getMonthlyRate())

employee.pay(new Salary(employee.getMonthlyRate())  + new Bonus(500))

console.log(employee.wallet + 0)

how you do it

(function () {

    var getWorkingDaysInMonth = function(date) {
        var days, daysInMonth, isWorkingDate;
        isWorkingDate = function(date) {
            var day;
            day = date.getDay();
            return day !== 0 && day !== 6;
        };
        daysInMonth = new Date(date);
        daysInMonth.setMonth(daysInMonth.getMonth() + 1);
        daysInMonth.setDate(0);
        daysInMonth = date.getDate();
        days = 0;
        while (days < daysInMonth) {
            if (isWorkingDate(date)) {
                days++;
            }
            date.setDate(date.getDate() + 1);
        }
        return days;
    };

    var extend = function (child, parent) {
        for (var key in parent) {
            if ({}.hasOwnProperty.call(parent, key)) {
                child[key] = parent[key];
            }
        }
        function ctor() {
            this.constructor = child;
        }

        ctor.prototype = parent.prototype;
        child.prototype = new ctor();
        child.__super__ = parent.prototype;
        return child;
    };


    var usualIQ = 120;
    var workingHoursPerDay = 6;


    function Money(money) {
        this.money = typeof money === 'number' ? money : 0;
    }

    Money.prototype.add = function(money) {
        this.money += money;
    };

    Money.prototype.valueOf = function() {
        return this.money;
    };

    Money.prototype.toString = function() {
        return this.money;
    };


    function Wallet() {
        return Wallet.__super__.constructor.apply(this, arguments);
    }
    extend(Wallet, Money);


    function Salary() {
        return Salary.__super__.constructor.apply(this, arguments);
    }
    extend(Salary, Money);


    function Bonus() {
        return Bonus.__super__.constructor.apply(this, arguments);
    }
    extend(Bonus, Money);


    function Human() {}

    Human.prototype.hi = function() {
        throw new Error("doesn't implemented");
    };


    function Person(name, iq) {
        this.name = name;
        this.iq = iq;
    }

    extend(Person, Human);

    Person.prototype.isClever = function () {
        return this.iq > usualIQ;
    };

    Person.prototype.hi = function () {
        return "Hi, my name is " + this.name + ", my iq is " + this.iq;
    };


    function Employee(name, iq, rate) {
        this.name = name;
        this.iq = iq;
        this.rate = rate;
        this.wallet = new Wallet();
    }
    extend(Employee, Person);

    Employee.prototype.getMonthlyRate = function() {
        var date;
        date = new Date();
        return getWorkingDaysInMonth(date) * this.rate * workingHoursPerDay;
    };

    Employee.prototype.pay = function(salary) {
        return this.wallet.add(salary);
    };

    Employee.prototype.hi = function () {
        return 'Bip Bop...';
    };


    var employee = new Employee('Alexey', 121, 20);
    console.log(employee.hi());
    console.log(employee.isClever());
    console.log(employee.getMonthlyRate());

    employee.pay(new Salary(employee.getMonthlyRate()) + new Bonus(500));

    console.log(employee.wallet + 0);

}).call(this);