Lodge It

<script type="text/javascript" src="prototype.js"></script>
<script type="text/javascript">
var Mammal = Class.create();
Mammal.prototype = {
    initialize : function(name) {
        this.name = name;
        this.offspring = [];
        this.type = "Mammal";
    },
    toString : function() {
        return "[" + this.type + ": " + this.name + "]";
    },
    haveABaby : function(name) {
        if (name == undefined) {
            name = "Baby " + this.name;
        }
        var newBaby = new this.constructor(name);
        this.offspring.push(newBaby);
        return newBaby;
    }
};

var Human = Class.create();
Human.prototype.constructor = Human;
Human.prototype = Object.extend(new Mammal, {
    initialize : function(name) {
        this.name = name;
        this.type = "Human";
    },
});

var hoge = new Human("Hoge");
var fuga = hoge.haveABaby("Fuga");

var takashi = new Human("Takashi");
var kay = takashi.haveABaby("Kay");
alert(takashi.offspring[0].toString());
</script>