functional js implement reduce

copycat.js

module.exports = function reduce(arr, fn, initial) {
	function justDoOne(index, value) {
		if (index >= arr.length) {
			return value
		}
		return justDoOne(index + 1, fn(value, arr[index]))
	}
	
	return justDoOne(0, initial)
}

goodsolution.js

function reduce(arr, fn, initial) {
    return (function reduceOne(index, value) {
      if (index > arr.length - 1) return value
      return reduceOne(index + 1, fn(value, arr[index], index, arr))
    })(0, initial)
}

mysolution.js

module.exports = function reduce(arr, fn, initial) {
	var acc = initial
	arr.forEach(function(elem) {
		acc = fn(acc, elem)
	})
	return acc
}