Sure, _some_ problems can be solved elegantly and efficiently with it, but a lost of the time it just impedes readability, and maintainability of the code. A `for of` loop (or your C-styled for loop) would sometimes be better suited.
For example, the "use reduce to run asynchronous calls in sequence" is an important pattern, and was pretty much the best way to do this (or another way that was basically equivalent) before async/await. With async/await, though, it's trivial (and in my opinion more readable) to just do this in a for loop with await. So I found it a bit odd that his reducer function used async/await syntax.
There was an article on HN recently about "don't compromise simplicity for dogma", and I think that applies here.
The performance differences can be quite marked as well.
I wrote some code the other day that could have been done with forEach more readably but I just used regular for loops because I was working with what was effectively a 3D array (grid/cell/contents) and know that for can be nearly twice as fast as foreach.
Sure, every problem can be solved in a functional way, but JavaScript is not a purely functional language. Why limit yourself to a subset of the language? IMO, you should use the best tool you can for the problem. Sometimes that's reduce, sometimes it's not.
Also, I love Ruby (and used Elixir), and it's not really a comparison that makes sense, they're different languages with different APIs, syntax, and there's a category of problems in JS you never have to think about when using Erlang/Elixir, or Ruby. I could say that I'm used to seeing maps and folds in Haskell code; doesn't really mean anything in this discussion.
sidenote, i really do enjoy code typeset with typewriter fonts for short codeblocks like in the article
Where I find it fails is when there's a ton of imperative code that's really hard to understand the premise. The beauty of functional programming is that you can take these stanzas and break them into nicely testable, named functions.
[
{id: 1, name: 'Jane'},
{id: 2, name: 'John'}
]
{
1: {id: 1, name: 'Jane'},
2: {id: 2, name: 'John'}
}