This isn't meant to be an exhaustive guide on how to write an NPM module. This guide is meant to be a simple working example where you can see a basic working module and easily adapt this to create your own module.
You can see the basic structure is
A St.George Bank IPG Hosted Payment Page (HPP) plugin for WooCommerce. This plugin will allow you to accept payments via your St.George Bank online Merchant Account using your WooCommerce shopping cart
Download the module here.
Here are the steps to