"JS Building Blocks" in the HubSpot CMS is entering a private beta. This source code is a Hello World demo for those in the beta program. If you are interested in signing up please follow this link and fill out the form. Without access to the beta, critical features of JS Buidling blocks will not work for you.
If you are in the private beta, you should have received seperate and specific documentation on how to use this project with your account.