Everything you have said. Don't forget currying. By the way, you don't always have the option to go functional on an existing or even a new project. All depends on the team and their willingness to learn new concepts.

I'm learning this so don't know every concept of FP. I think about high order and pure functions with all your stuff, with forEach in some cases.

the same things :) I'm experimenting with elixir atm so I have to add recursions :) for the pure functional programming I would have to learn a lot more.