Butterfly state machine ( http://harkablog.com/dynamic-state-machines.html ) in javascript

butterflymachine.js

#!/usr/bin/node

/* butterfly state machine */

var Egg = function(species) {

    this.species = species;
    console.log("An egg");

    this.hatch = function() {
        this.__proto__ = new Catterpiller();
        console.log(this.species, "hatching, check out my", this.legs, "legs!");
    }
};

var Catterpiller = function() {

    this.legs = 16;

    this.crawl = function() { 
        console.log("crawling");
    };

    this.eat = function() { 
        console.log("eating");
    };

    this.pupate = function() {
        this.__proto__ = new Pupa();
        console.log(this.species, "Pupating!");
    }
};

var Pupa = function() {

    this.emerge = function() {
        this.__proto__ = new Butterfly();
    }
};

var Butterfly = function() {

    this.fly = function() { 
        console.log("flying");
    };

    this.eat = function() { 
        console.log("eating");
    };

    this.reproduce = function() {
        return new Egg(this.species);
    }
};


critter = new Egg('Morpho menelaus');
critter.hatch();
critter.crawl();
critter.eat();
critter.pupate();
critter.emerge();
critter.fly();
offspring = critter.reproduce();

That's all well and good, but IIRC __proto__ is an implementation detail. This may work in node, and most browsers, but in I believe it will fail in some IE browsers.

According to an answer on http://www.quora.com/JavaScript/What-is-the-difference-between-__proto__-and-prototype, you should not use it.