MooTools

var Animal = new Class({

    initialize: function(name) {
        this.name = name;
    }

});

var Cat = new Class({
    Extends: Animal,

    talk: function() {
        return 'Meow!';
    }

});

var Dog = new Class({

    Extends: Animal,

    talk: function() {
        return 'Arf! Arf!';
    }

});

var animals = {
    a: new Cat('Missy'),
    b: new Cat('Mr. Bojangles'),
    c: new Dog('Lassie')
};

Object.each(animals, function(animal) {
    alert(animal.name + ': ' + animal.talk());
});

// alerts the following:
//
// Missy: Meow!
// Mr. Bojangles: Meow!
// Lassie: Arf! Arf!