classy.js

(function () {
  var initializing = false
    , superPattern = /xyz/.test(function () { xyz; }) ? /\b_super\b/ : /.*/;

  Object.subClass = function (properties) {
    var _super = this.prototype;

    initializing = true;
    var proto = new this();
    initializing = false;

    for (var name in properties) {
      proto[name] = typeof properties[name] == 'function' &&
                    typeof _super[name] == 'function' &&
                    superPattern.test(properties[name]) ?
        (function (name, fn) {
          return function () {
            var tmp = this._super;

            this._super = _super[name];
            var ret = fn.apply(this, arguments);
            this._super = tmp;

            return ret;
          };
        }(name, properties[name])) :
        properties[name];
    }

    function Class() {
      if (!initializing && this.init) {
        this.init.apply(this, arguments);
      }
    }

    Class.prototype = proto;
    Class.constructor = Class;
    Class.subClass = arguments.callee;
    return Class;
  };
}());