def.js

/*
 *    def.js: Simple Ruby-style inheritance for JavaScript
 *
 *    Copyright (c) 2010 Tobias Schneider
 *    This script is freely distributable under the terms of the MIT license.
 */
(function(global) {

  // used to defer setup of superclass and plugins
  var deferred;

  function addPlugins(plugins) {
    augment(this.prototype, plugins);
    return this;
  }

  // TODO: Ensure we fix IE to iterate over shadowed properties
  // of those further up the prototype chain. There is also a
  // bug in Safari 2 that will match the shadowed property and
  // the one further up the prototype chain.
  function augment(destination, source) {
    for (var key in source) {
      destination[key] = source[key];
    }
  }

  // dummy subclass
  function Subclass() { }

  function def(klassName, context) {
    context || (context = global);

    // create class on given context (defaults to global object)
    var Klass =
    context[klassName] = function Klass() {
      // called as a constructor
      if (this != context) {
        // allow the init method to return a different class/object
        return this.init && this.init.apply(this, arguments);
      }
      // called as a method
      // defer setup of superclass and plugins
      deferred._super = Klass;
      deferred._plugins = arguments[0] || { };
    };

    // add static helper method
    Klass.addPlugins = addPlugins;

    // called as function when not
    // inheriting from a superclass
    deferred = function(plugins) {
      return Klass.addPlugins(plugins);
    };

    // valueOf is called to setup
    // inheritance from a superclass
    deferred.valueOf = function() {
      var Superclass = deferred._super;
      if (!Superclass) return Klass.valueOf();

      Subclass.prototype = Superclass.prototype;
      Klass.prototype = new Subclass;

      Klass.superclass = Superclass;
      Klass.prototype.constructor = Klass;
      Klass.addPlugins(deferred._plugins);

      deferred._super = deferred._props = null;
      return Klass.valueOf();
    };

    return deferred;
  }

  // expose
  global.def = def;
})(this);

gistfile2.js

// Example

def ('Person') ({
  'init': function(name) {
    this.name = name;
  },

  'speak': function(text) {
    alert(text || 'Hi, my name is ' + this.name);
  }
});

def ('Ninja') << Person ({
  'kick': function() {
    this.speak('I kick u!');
  }
  , 'speak': function(text){
    alert("My function: " + text);
  }
});

var ninjy = new Ninja('JDD');
ninjy.speak("whoa!");
ninjy.kick();