Как добавить константы к объекту Date

[VladBD]

Date.SEC= 1000;
Date.MIN = 60*Date.SEC;
Date.HOUR= 60*Date.MIN;
Date.DAY = Date.HOUR*24;

Date.daysofWeek = new Array("вс","пн","вт","ср","чт","пт","сб");
Date.months = new Array("01","02","03","04","05","06","07","08","09","10","11","12");

собственно пример из книги - но что-то ругается...