[jasonkester]

When used correctly it shouldn't produce any side-effects outside the mapping of each element.

But that's just a social convention. There's nothing stopping you from doing other things during your map or reduce.

In practice, the only difference between Map, Reduce and a For loop is that the first two return things. So depending on whether you want to end up with an array containing one item for each pass through the loop, "something else", or nothing, you'll use Map, Reduce or forEach.

You can still increment your global counters, launch the missiles or cause any side effects you like. "using it correctly" and not doing that is just a convention that you happen to prefer.

[hnedeotes]

That is true (less so in FP languages though), but the for loop doesn't either - indeed I do prefer it most of the times, I think its a reasonable expectation to provide the most intention revealing constructs when possible, it's also easier to spot "code smells" when using those. The exceptions I make is when there's significant speed concerns/gains, when what you're doing is an actual loop, when the readability by using a loop is improved.

(and I haven't read the article so not even sure I agree with the example there, this was more in general terms)