There's a huge difference between "you can write functional methods in any language" and "writing functional code is default/idiomatic". Erlang doesn't support

There's a huge difference between "you can write functional methods in any language" and "writing functional code is default/idiomatic". Erlang doesn't support mutation at all, for example, and uses immutable types for everything. But it does let you send messages to other processes, which is a side-effect, so Erlang is not purely functional. But that doesn't mean that JavaScript is somehow just as functional as Erlang. Because it's not.