How things are done everywhere. Versus how I want them to be done.

extension-patterns.js

// tired of this extension pattern
var Cow = AnimalFactory({
  getVoice: function() { return 'moo'; }),
  numLegs: 4,
  name: 'Cow',
})

// propose this one instead
var MutantCow = AnimalFactory.extend()
  .getVoice(function() { return 'moo'; })
  .numLegs(5)
  .name('Cow');

var Crow = AnimalFactory.extend()
  .getvoice(function() { return 'CAWW!'; } // no method error
  .numlegs(2) // no method error

// what other things can I configure?
// the configuration object gives me a good hint
Object.keys(AnimalFactory.configure())


function AnimalFactory() {
  var classConfig = {};
  var  = {};

  var _classAttributes = {};

  //downside: lots of boilerplate for the owner
  classConfig.getVoice = function(voiceFunction) {
    _classAttributes.getVoice = voiceFunction;
    return classConfig;
  };

  classConfig.numLegs = function(numLegs) {
    _classAttributes.numLegs = numLegs;
    return classConfig;
  };

  classConfig.name = function(name) {
    _classAttributes.name = name;
    return classConfig;
  };

  this.extend = function() {
    return (new AnimalFactory())._configure();
  };

  this._configure = function() {
    return classConfig;
  };

  this.instantiate = function() {
    var instance = {};

    instance.speak = function() {
      alert(_classAttributes.getVoice());
    };

    instance.walk = function() {
      alert([
        _classAttributes.name,
        "is walking with its",
        _classAttributes.numLegs,
        "legs"
      ].join(' '));
    };

    return instance;
  }
}