(function($) {
    $.fn.checkDate = function(txtDate) {
        var currVal = '';
        var typeVal = '';
        if (txtDate != '' && txtDate != undefined) {
            currVal = txtDate;
            typeVal = "Prüfung auf Objekt:";
        } else {
            currVal = this.val();
            typeVal = "Prüfung auf HTML Element:";
        }
       
        if (currVal == '')
            return false;
    
        //Declare Regex 
        //var rxDatePattern = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;
        var rxDatePattern = /^(\d{1,2})(\/|-|.)(\d{1,2})(\/|-|.)(\d{4})$/;
        var dtArray = currVal.match(rxDatePattern); // is format OK?

        if (dtArray == null)
            return false;

        //Checks for dd/mm/yyyy format.
        dtDay = dtArray[1];
        dtMonth = dtArray[3];
        dtYear = dtArray[5];
    
        if (dtMonth < 1 || dtMonth > 12)
            return false;
        else if (dtDay < 1 || dtDay > 31)
            return false;
        else if ((dtMonth == 4 || dtMonth == 6 || dtMonth == 9 || dtMonth == 11) && dtDay == 31)
            return false;
        else if (dtMonth == 2) {
            var isleap = (dtYear % 4 == 0 && (dtYear % 100 != 0 || dtYear % 400 == 0));
            if (dtDay > 29 || (dtDay == 29 && !isleap))
                return false;
        }
        return typeVal + ' ' + true;
    }
}(jQuery));

 var myDate = '25.05.2011';
 $("#Output").val('*' + $().checkDate(myDate) )  ;