function extend(Child, Parent) {
        var F = function() { }
        F.prototype = Parent.prototype
        Child.prototype = new F()
        Child.prototype.constructor = Child
        Child.superclass = Parent.prototype
    }

 function foo() {}
    foo.prototype.identify = function() {
        return "I'm a foo";
    }
    
    function bar() {}
    extend(bar, foo)
    bar.prototype.identify = function() {
        return "I'm a bar and " +
            this.constructor.superclass.identify.apply(this, arguments);
    }
    
    function zot() {}
    extend(zot, bar)
    zot.prototype.identify = function() {
        return "I'm a zot and " +
            this.constructor.superclass.identify.apply(this, arguments);
    }

 f = new foo();
    
    alert(f.identify()); // "I'm a foo"
    
    b = new bar();
    
    alert(b.identify()); // "I'm a bar and I'm a foo"
    
    z = new zot();
    
    alert(z.identify()); // stack overflow