Refactor towards dependency injection

Author here. I am happy to hear some comments from you HN readers. This is the start of my attempt to blog more often, get some experience in writing and help others about a topic I think I have some experience in.

It is understandable that the topic is kinda junior level to most of you, as you are not the target group to learn from it. Nevertheless, more experienced programmers and writers can hopefully give me a few tips. Anything welcome!