Eli Weinstock-Herman explains how to use Azure Functions to create dynamic content on an otherwise-static page:
My personal website is a static site: 100% HTML, JS, and CSS files with no server-side processing. I have custom code that pulls data from a variety of sources and builds updated versions of the files from templates, which are then deployed to the host. I do this to move the CPU latency of building the pages to my time, instead of charging it to visitors on each page hit. While I have a host, a strategy like this means I could also choose to host for free via github or similar services.
So there’s a great benefit to the reader and our wallet, but no server-side execution makes things like contact forms trickier. Luckily, Azure Functions or AWS Lambda can be used as a webhook to receive the form post and process it, costing nothing near nothing to use (AWS and Azure both offer a free tier for 1M requests/month and 400,000 GB-seconds of compute time).
Eli has a working example in the post, which I recommend checking out.