var a = moment().subtract(1, 'day');
var b = moment().add(1, 'day');
moment.max(a, b); // b
var friends = fetchFriends(); /* [{name: 'Dan', birthday: '11.12.1977'}, {name: 'Mary', birthday: '11.12.1986'}, {name: 'Stephan', birthday: '11.01.1993'}]*/
var friendsBirthDays = friends.map(function(friend){
return moment(friend.birthday, 'DD.MM.YYYY');
});
moment.max(friendsBirthDays); // '11.01.1993'