Functional programming is kind of thing which usually is not too famous. You have to come to this one day and will be completely different.
What is this? Long story short, it's method of thinking. Personally me prefer to treat it as a stream when you do not do something, you are converting one items (inputs) to another (results), using some computational logic.
There are not a lot of resources for functional programming in JS at all, so my recommendation will be this link https://medium.com/@cb.yannick/functional-programming-with-typescript-part-1-3f7167a2c0ad

So what about angular? I did not found any good resources for Angular, maybe because with FP it's pretty common to avoid Dependency injection, which is a core and main part of Angular.

So I will try in next articles to show what and how I apply functional programming with Angular.