reduce.js

function reduce(f, init, col) {
  let result = init
  for (i = 0; i < col.length; i++)
    result = f(result, col[i], i, col)
  return result
}

function recursiveReduce(f, init, col) {
  function $(i, result) {
    return i === col.length
      ? result
      : $(i + 1, f(result, col[i], i, col))
  }

  return $(0, init)
}

function range(from, to) {
  const col = [] 
  for (i = from; i < to; i++)
    col.push(i)
  return col
}

const sum = (a, b) => a + b

// použití

reduce(sum, 0, [1, 2, 3])
recursiveReduce(sum, 0, [1, 2, 3])

// bacha na stack při rekurzi!

reduce(sum, 0, range(0, 1000000))
recursiveReduce(sum, 0, range(0, 1000000))// StackOverflow error