JS array map via Comonad (https://gist.github.com/quelgar/4661081)

array_comonad.js

//https://gist.github.com/quelgar/4661081

const daggy = require('daggy');
const {range} = require('ramda');

// type to hold an index and the array
const Pointer = daggy.tagged('i', 'a')

// Comonad instance
Pointer.prototype.extract = function() { return this.a[this.i] }

// builds a pointer of pointers where each element is focused.
Pointer.prototype.extend = function(f) {
  return Pointer(this.i, range(0, this.a.length).map(i => f(Pointer(i, this.a))))
}

const jsmap = (f, xs) => Pointer(0, xs).extend(({i: i, a: a}) => f(a[i], i, a)).a

// our map gets 3 args that are "context aware" - current el, index, and rest of the array
jsmap((e, i, xs) => e + i, [1,2,3,4,5])
//=> [1,3,5,7,9]