It was an introduction to reactive programming with the RxJS library, with examples that are relevant to Angular apps. I didn’t know this guide existed. If I had, I would have started here first! If I had, I still wouldn’t have understood RxJS immediately, but I would at least have a better focus as I ventured to other RxJS guides. Mostly thanks to Observables in Angular which showed the most common RxJS usage patterns.
I was mildly disappointed the Practical Usage page had only two examples, and one of them was the type-ahead autocomplete mechanism already covered in Tour of Heroes. At least that one had a breakdown of how the asynchronous processing pipeline worked to accomplish its goal. The other example “Exponential backoff” had no such explanation. Just an overly optimistic claim “With observables, it is very easy” before we were tossed a chunk of code with no comments nor a breakdown of what it did. Definitely room for improvement here.