I have been playing with GitHub Actions quite a bit recently at YNAB and for some personal projects and it has been fun. Most recently I got xertz, my static site generator project, running on GitHub Actions for build/test and releases to the npm registry.
We love TypeScript at YNAB. One of our main modules is something we call the “Shared Library” and it is a quite large TypeScript project. Actually, it’s comprised of 3 library projects and 3 test projects. It’s big. And, it was initially written using TypeScript namespaces, before TypeScript had support for ES modules.