Compare these two solutions:

map = (fn, [head, …tail]) => {
 if (head === undefined) {
   return [];
 }
 return [fn(head), …map(fn, tail)];
};
map2 = (fn, arr) => {
 let result = [];
 for (let i = 0; i < arr.length; i++) {
   result[i] = fn(arr[i]);
 }
 return result; 
 
};
let test_data = [];
for (let i = 0; i < 5000; i++) {
 test_data.push(i);
}
let double = (x)=> x * 2;
map2(double, test_data);

Map Recursive:

real 0m2.172s
user 0m2.026s
sys 0m0.154s

Map Iterative:

real 0m0.087s
user 0m0.063s
sys 0m0.022s

While the recursive solution is neat, slick, etc — it comes at the cost of a huge performance hit..