Getting Undefined error while using extended java script

Summary

I have extended the java script of product listing style widget. But when I tried to bind the observable from extended js to the template, it is giving error.

Content

I have a standard widget Product listing style widget, I have extended the java script of the same from admin console. Within the extended java script I have created an observable and I am trying to bind that observable to the widget template code. But when I tried that I am getting undefined error in the console. Can you please help me in this.

Code Snippet

//template code

  <span data-bind="text: firstname"></span>

//extended js

/**
 * @fileoverview extendproductListing_v15.js.
 *
 * @author 
 */
define(
  //---------------------
  // DEPENDENCIES
  //---------------------
  ['knockout','viewModels/productListingViewModelFactory','CCi18n','ccConstants', 'pubsub', 'pageLayout/product', 'storageApi', 'ccStoreConfiguration'],

  //-----------------------
  // MODULE DEFINITION
  //-----------------------
  function (ko, ProductListingViewModelFactory, CCi18n, CCConstants, pubsub, Product, storageApi, CCStoreConfiguration) {
      var widgetModal;
           var repositoryId = widget.category().repositoryId;
      console.log("rep id"+repositoryId);

    "use strict";
    return {
       
     // myValue: ko.observable(false),