2016 Update

Task/Happy-numbers/JavaScript/happy-numbers-2.js

@@ -0,0 +1,25 @@
+(() => {
+    'use strict';
+
+    // isHappy :: Int -> Bool
+    function isHappy(n) {
+        let f = n => n.toString()
+            .split('')
+            .reduce((a, x) => a + Math.pow(parseInt(x, 10), 2), 0),
+            p = (s, n) => n === 1 ? true : (
+                s.has(n) ? false : p(s.add(n), f(n))
+            );
+        return p(new Set(), n);
+    }
+
+    // TEST
+
+    // range :: Int -> Int -> [Int]
+    let range = (m, n) => Array.from({
+        length: Math.floor(n - m) + 1
+    }, (_, i) => m + i);
+
+    return range(1, 50)
+        .filter(isHappy)
+        .slice(0, 8);
+})()