This is a simple barebone demo for Azure SWAG (Static Web Apps on GitHub). You can use it as a template for your own apps.
It includes a website using HTML + JavaScript and an example Node.js API. See it live here.
Click on Use this template on GitHub, then click on the button below to deploy your own (for free):
TL;DR:
It's an all-inclusive hosting service for web apps with serverless APIs built using JavaScript, based on continuous deployment from a GitHub repository.
For the longer version with the deployment instructions, see this full length article.
You can also take a look at the official docs.