From what I can see functional programming is significant but not only part of javascript allonge and javascript spessore contains references to fp but it doesn't seem to be focus of this book
"Spessore" is about OOP, but described from unusual angle: it reminds me of "The Little Java, a Few Patterns" in this regard. It's a great description of how and why OOP works, from the most basic concepts up.
Reg's articles on FP in JS and Ruby let me fill the gaps in my knowledge I had because of having no formal education in maths. I was interested in FP for years, and I learned much about it on my own, but Reg's texts made it all "click" for me. I definitely recommend reading all of them; unless you're really familiar with this stuff, from both theoretical and practical sides, I can guarantee that you'll learn something new and useful.
Really, go read them. See also https://leanpub.com/coffeescript-ristretto if you prefer CS.