Date.dayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
Date.abbrDayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
Date.monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];
Date.abbrMonthNames = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
Date.firstDayOfWeek = 1;
Date.format = 'dd/mm/yyyy';
//Date.format = 'mm/dd/yyyy';
//Date.format = 'yyyy-mm-dd';
//Date.format = 'dd mmm yy';
Date.fullYearStart = '20';
(function() {
    function add(name, method) {
        if( !Date.prototype[name] ) {
            Date.prototype[name] = method;
        }
    };
    add("isLeapYear", function() {
        var y = this.getFullYear();
        return (y%4==0 && y%100!=0) || y%400==0;
    });
    add("isWeekend", function() {
        return this.getDay()==0 || this.getDay()==6;
    });
    add("isWeekDay", function() {
        return !this.isWeekend();
    });
    add("getDaysInMonth", function() {
        return [31,(this.isLeapYear() ? 29:28),31,30,31,30,31,31,30,31,30,31][this.getMonth()];
    });
    add("getDayName", function(abbreviated) {
        return abbreviated ? Date.abbrDayNames[this.getDay()] : Date.dayNames[this.getDay()];
    });
    add("getMonthName", function(abbreviated) {
        return abbreviated ? Date.abbrMonthNames[this.getMonth()] : Date.monthNames[this.getMonth()];
    });
    add("getDayOfYear", function() {
        var tmpdtm = new Date("1/1/" + this.getFullYear());
        return Math.floor((this.getTime() - tmpdtm.getTime()) / 86400000);
    });
    add("getWeekOfYear", function() {
        return Math.ceil(this.getDayOfYear() / 7);
    });
    add("setDayOfYear", function(day) {
        this.setMonth(0);
        this.setDate(day);
        return this;
    });
    add("addYears", function(num) {
        this.setFullYear(this.getFullYear() + num);
        return this;
    });
    add("addMonths", function(num) {
        var tmpdtm = this.getDate();
        
        this.setMonth(this.getMonth() + num);
        
        if (tmpdtm > this.getDate())
            this.addDays(-this.getDate());
        
        return this;
    });
    add("addDays", function(num) {
        this.setDate(this.getDate() + num);
        return this;
    });
    add("addHours", function(num) {
        this.setHours(this.getHours() + num);
        return this;
    });
    add("addMinutes", function(num) {
        this.setMinutes(this.getMinutes() + num);
        return this;
    });
    add("addSeconds", function(num) {
        this.setSeconds(this.getSeconds() + num);
        return this;
    });
    add("zeroTime", function() {
        this.setMilliseconds(0);
        this.setSeconds(0);
        this.setMinutes(0);
        this.setHours(0);
        return this;
    });
    add("asString", function() {
        var r = Date.format;
        return r
            .split('yyyy').join(this.getFullYear())
            .split('yy').join((this.getFullYear() + '').substring(2))
            .split('mmm').join(this.getMonthName(true))
            .split('mm').join(_zeroPad(this.getMonth()+1))
            .split('dd').join(_zeroPad(this.getDate()));
    });
    Date.fromString = function(s)
    {
        var f = Date.format;
        var d = new Date('01/01/1977');
        var iY = f.indexOf('yyyy');
        if (iY > -1) {
            d.setFullYear(Number(s.substr(iY, 4)));
        } else {
            d.setFullYear(Number(Date.fullYearStart + s.substr(f.indexOf('yy'), 2)));
        }
        var iM = f.indexOf('mmm');
        if (iM > -1) {
            var mStr = s.substr(iM, 3);
            for (var i=0; i<Date.abbrMonthNames.length; i++) {
                if (Date.abbrMonthNames[i] == mStr) break;
            }
            d.setMonth(i);
        } else {
            d.setMonth(Number(s.substr(f.indexOf('mm'), 2)) - 1);
        }
        d.setDate(Number(s.substr(f.indexOf('dd'), 2)));
        if (isNaN(d.getTime())) {
            return false;
        }
        return d;
    };
    
    var _zeroPad = function(num) {
        var s = '0'+num;
        return s.substring(s.length-2)
    };
    
})();
Date.dayNames = ['Sonntag', 'Montag', 'Dienstag', 'Mittwoch', 'Donnerstag', 'Freitag', 'Samstag'];
Date.abbrDayNames = ['So', 'Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa'];
Date.monthNames = ['Januar', 'Februar', 'März', 'April', 'Mai', 'Juni', 'Juli', 'August', 'September', 'Oktober', 'November', 'Dezember'];
Date.abbrMonthNames = ['Jan', 'Feb', 'Mrz', 'Apr', 'Mai', 'Jun', 'Jul', 'Aug', 'Sep', 'Okt', 'Nov', 'Dez'];