This is an open source project for a SharePoint Hosted Add-In, feel free to use it as you like. You can see this as a template for your SharePoint Add-In containing a typical solution to communicate with the add-in web as well as the host web or with an external database. This project will bring you different JS files, as you can see as examples of how to work with different data sources. For example communication with an external REST API, internal list in the Add-In web or with a list in the host web. You will see how to read data from A SP list in the app web into a APP Part as well as in a Immersive App. Enjoy!