Code
function getLastDateOfMonth(year, month){
return (new Date( (new Date(year,month+1,1))-1 )).getDate();
}
ok( getLastDateOfMonth(2000, 0) == 31 );
ok( getLastDateOfMonth(2000, 1) == 29 );
ok( getLastDateOfMonth(2001, 1) == 28 );
ok( getLastDateOfMonth(2004, 1) == 29 );
ok( getLastDateOfMonth(2100, 1) == 28 );