Add reduce example

Author: tshemsedinov

JavaScript/6-reduce.js

@@ -0,0 +1,8 @@
+'use strict';
+
+const reduce = (fn, acc, [cur, ...rest]) => (
+  cur === undefined ? acc : reduce(fn, fn(acc, cur), rest)
+);
+
+const res = reduce((a, b) => a + b, 0, [1, 2, 3, 4, 5, 6, 7, 8, 9]);
+console.log({ res });