Well, reduce is a recursion with an accumulator. Did you had something special in mind?

In hindsight the second solution was obvious :) But can you explain your ideal solution more? Is it something that can be accomplished in Javascript?

Why would you write mind-boggling recursion by hand, and not use a nice combinator that comes pre-debugged?

Because I had a brain fart and though "reduce" was "scan", and I didn't want to initialize an array.