index.js

  var CatClass = AnimalClass.extend(function (super_) {
  	return {
    	name: 'CatClass',
      method: {
        constructor: function (params) {
          super_.constructor.call(this, params);
          this._voice = 'mew';
        },
        cry: function() {
        	return super_.cry(this._name, this._voice);
        }
      }
    }
  });