gistfile1.js

// extend.js
define(function (require) {

    var _ = require("vendor/underscore");

    var ctor = function () {};

    var inherits = function (parent,protoProps,staticProps) {
        var child;
        if (protoProps && protoProps.hasOwnProperty("constructor")) {
            child = protoProps.constructor;
        } else {
            child = function () { return parent.apply(this,arguments); };
        }
        _.extend(child,parent);
        ctor.prototype = parent.prototype;
        child.prototype = new ctor();
        if (protoProps) _.extend(child.prototype,protoProps);
        if (staticProps) _.extend(child,staticProps);
        child.prototype.constructor = child;
        child.__super__ = parent.prototype;
        return child;
    };

    function extendThis (protoProps,staticProps) {
        var child = inherits(this,protoProps,staticProps);
        child.extend = extendThis;
        return child;
    }

    return extendThis.bind(extendThis);
});

// Usage

define(function (require) {
  
  var extend = require("extend");
  
  var MyClass = extend({
    init: function (options) {
      console.log("MyClass.init");
    }
  });
  
  var myClass = new MyClass();
  myClass.init({}); // MyClass.init
  
  var MySubClass = MyClass.extend({
    init: function (options) {
      MyClass.prototype.init.call(this,options);
      console.log("MySubClass.init");
    }
  });
  
  var mySubClass = new MySubClass();
  mySubClass.init(); // MyClass.init + MySubClass.init
  
});