Nice ones! My first TS project was with a C# guy, so we had some virtual classes, no good) Anyways, the TS community itself does not seem to enforce OOP stuff too much — Angular / mobx do.

On the other hand, I don't know why the DI stuff never caught on in he js world — it should be good for testablity (better than build-time magic at least)?

Honestly, DI is really a thing of the OO-Obsessed world when everything has to be a class and instantiated.

In the JS/TS world, we mostly use Interface/Type to describe constraints, and most of the module export function or group of methods in a const (namespace, module,...) but the caller does not have to know if it is a class or just a object with some methods, and does not do a "new ..." or @inject... anymore. Much simpler, much more intent driven, and you can remove a lot of boilerplate code (which DI still is)

Now, one of the value of DI is for testing, and one way to accomplish module compartmentalization, is with module-alias. It does not the granularity that DI needs, but I would argue that if more is needed, it perhaps because the testing and mocking got a little too out of hands. In our experience, thanks to Kubernetes, we try to mock less, and have our test running mostly with real services.