[mushyhammer]

> what to do when going from n to n+1

You mention the only worthwhile exception: sums and other 3-character operation.

If you’re using reduce to construct objects you’re just better off with a for loop. Having a random awkward named function that only makes sense when plugged into reduce is not any better than just have a function that includes the loop itself:

    - newArray = array.reduce(operation, [])
    + newArray = operation(array)

If you’re used to having infinite chains of loops then of course that’s not going to work.

The problem is that reduce can do anything and most people use it to do anything. It has no advantage over regular for loops unless you’re proficient with real functional programming (if you use forEach() in JavaScript, you’re not)

> With both, you only have to write what happens to one element, and it will happen to the whole collection. This makes code easier to read.

Filter and map are ok. Filter, map and reduce are not, at least not in JavaScript. Try writing the equivalent for loop and you’ll find that it’s just as simple to follow.