the way JS does closures, and the mandatory async nature of everything, leads to a world where you're working with functions a lot more than you would be in languages in the same family (garbage collected, lenient, a la python and ruby). from there, functional programming concepts like partial application and currying start to pop up. if you dive into frameworks like react.js, you start to encounter pure functions and immutability. it's not what I would call a "functional programming language", but I find the concepts show up more than usual, and I think that's because functions are one of the more advanced primitives in the language