Extend function from superclass in Backbone.js

Hi guys,

How can i extend a function from a superclass in Titanium? My superclass:

exports.definition = {
config: {
    // config of superclass
},
extendModel: function(Model) {
    _.extend(Model.prototype, {
        test : function (){
            return 'superClass';
        }
    });
 
    return Model;
}
};

exports.definition = {
config: {
  // config of subclass
},
 
extendModel: function(SuperModel) {
    _.extend(SuperModel.prototype, {
        test : function (){
          //return 'superClass'
        }
    });
});

var a = Alloy.Collections.subModel;
var a = Alloy.createModel('subModel', { 
  className : 'A', 
});
console.log(a.test()); // console.log -> superClass