calculate days and months from a month and a number of days

dates-001.js

var task = (function(){

    var _days = [31,28,31,30,31,30,31,31,30,31,30,31];

    function addDays(date,days){
        date.setDate(date.getDate() + days);
        return date;
    }

    function isLeapYear(year){
        return year %  4 === 0 ;
    }

    function subtractDaysByMonthAndYear(currentMonth,numberOfDays){
        var days = numberOfDays-_days[currentMonth.month];
        if(currentMonth.month==1 && isLeapYear(currentMonth.year))
            days -=1;
        return days;
    }

    function increaseMonth(currentMonth){
        if(currentMonth.month>11){
            currentMonth.month=0;
            currentMonth.year++;
        }
        return currentMonth;
    }


    return {

        fromMonth: function fromMonth(currentMonth,numberOfDays,monthsCounter){
            monthsCounter = monthsCounter || 0;
            currentMonth = increaseMonth(currentMonth);
            var days = subtractDaysByMonthAndYear(currentMonth,numberOfDays);
            currentMonth.month++;
            return (_days[currentMonth.month]>=days) ? [++monthsCounter,days] : fromMonth(currentMonth,days,++monthsCounter);
        },

        addDays: function(date,days){
            return addDays(date,days);
        }

    };

})();

var  currentMonth = {
    month:2,
    year:2016
};

console.log(task.fromMonth(currentMonth,1100));


currentMonth = {
    month:2,
    year:2015
};

console.log(task.fromMonth(currentMonth,1100));