map.js

/*
 * Given two functions `head` and `tail`
 * Implement the array `map` function using this two fucntions.
 * Example: `map([1,2,3], (n) => n * 2) == [2,4,6]`
 */

const head = (array) => array[0];
const tail = (array) => array.slice(1, array.length);

/* Example: map([1,2,3], (n) => n * 2) === [2,4,6]
 */
const map = (array, fun) => {
  // implement this function
  if (array.length === 0) return [];
  return [fun(head(array))].concat(map(tail(array), fun));
};

console.log(map([1, 2, 3], (n) => n * 2));