classext.js

function $extend(inherit, b) {
    var base = b.$class;
    for (var m in base) {
        if (base.hasOwnProperty(k)) {
            inherit[k] = base[k];
        }
    }

    function ctor() {
        this.constructor = inherit;
    }
    ctor.prototype = base.prototype;
    inherit.prototype = new ctor();
    inherit.$super = base.prototype;
    return inherit;
}

var $AnimalClass, $Animal, $SnakeClass, $Snake, s, bf, bw;

$Animal = (function() {
    function Animal(name) {
        this.name = name;
    }

    Animal.prototype.move = function(x) {
        return this.name + ' moved ' + x + ' meters';
    }

    function create(name) {
        return new Animal(name);
    }
    create.$class = Animal;
    return create;
})();

$Snake = (function() {
    function Snake(name) {
        return Snake.$super.constructor.apply(this, [name]);
    }

    $extend(Snake, $Animal);
    Snake.prototype.move = function(x) {
        return 'Snake ' + Snake.$super.move.call(this, x);
    }

    function create(name) {
        return new Snake(name);
    }
    create.$class = Snake;
    return create;
})();

$Bird = function() {
    function Bird(name, flyable) {
        Bird.$super.constructor.apply(this, [name]);
        this.flyable = flyable;
    }

    $extend(Bird, $Animal);
    Bird.prototype.move = function(x) {
        if (this.flyable) {
            return this.fly(x);
        }
        return Bird.$super.move.call(this, x);
    };
    Bird.prototype.fly = function(x) {
        return this.name + ' flied ' + x + ' meters';
    };

    function create(name, flyable) {
        return new Bird(name, flyable);
    }
    create.$class = Bird;
    return create;
}();

s = $Snake('Alche');
console.log(s, s.move(3));

bw = $Bird('Duck', false);
console.log(bw, bw.move(5));

bf = $Bird('Hawk', true);
console.log(bf, bf.move(7));