Javascript is a multi-paradigm language as are most others people are mentioning in these threads. It shows in the specification for the language too: higher-order functions, anonymous functions, Array.map/filter/reduce, etc. Like it or not the language has facilities to enable programming in a functional style.

There are advantages to this approach like enabling different styles when appropriate.

There are disadvantages as well: you rely on the discipline of the programmers or tools to catch mistakes.

But there's nothing inherently wrong about thinking of programs in terms of FP ideas. There are other ways to think about programming than in terms of program counters, control flow statements, and procedures. It's not even idiomatic Javascript to write code that way!

JS is a more functional language than most people seem to think.

The tragic thing about TFA is that it's not an article but a chapter in a long series of posts and this is just one step along the way to showing how an FP style can manage the complexities of a non-trivially large JS code base.