Add functional recursive reduce

Author: tshemsedinov

JavaScript/e-reduce.js

@@ -5,3 +5,9 @@ const arr = [7, 10, 1, 5, 2];
 const sum = (acc, val) => (count++, acc + val);
 const res = arr.reduce(sum);
 console.log({ res, count });
+
+const reduce = (fn, acc, [cur, ...rest]) => cur === undefined ?
+  acc : reduce(fn, fn(acc, cur), rest);
+
+const res2 = reduce(sum, 0, arr);
+console.log({ res2 });