2016 Update

Task/Flatten-a-list/JavaScript/flatten-a-list-2.js

@@ -1,3 +1,18 @@
-let flatten = list => list.reduce(
-    (a, b) => a.concat(Array.isArray(b) ? flatten(b) : b), []
-);
+(function () {
+    'use strict';
+
+    // flatten :: Tree a -> [a]
+    function flatten(t) {
+        return (t instanceof Array ? concatMap(flatten, t) : t);
+    }
+
+    // concatMap :: (a -> [b]) -> [a] -> [b]
+    function concatMap(f, xs) {
+        return [].concat.apply([], xs.map(f));
+    }
+
+    return flatten(
+        [[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []]
+    );
+
+})();