diff --git a/index.js b/index.js
index 9bb9cd7..30ec052 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,33 @@
 var doubler = function(a, b) {
-}
+  if(typeof b === "function" ){
+    return b()*2+a()*2;
+  }
+  return a + a + b + b;
+};
 
 console.assert(doubler(4,2) === 12);
 console.assert(doubler(1,3) === 8);
 console.assert(doubler(-1,3) === 4);
+
+console.assert(doubler("a", "b") === "aabb");
+console.assert(doubler("coding", "rocks") === "codingcodingrocksrocks");
+
+function m3() {return 3; }
+function m4() {return 4; }
+function m2() {return 2; }
+function m1() {return 1; }
+
+console.assert(doubler(m4, m2) === 12);
+console.assert(doubler(m1, m3) === 8);
+
+function objectsEqual() {return a != b;}
+
+var a = { z: 42 , t: 7 }, b = { t: 7, z: 42 };
+
+console.assert(objectsEqual(a, b));
+console.assert(objectsEqual(b, a));
+
+objectsEqual(doubler({x1: 1, x2: 4}), {x1: 2, x2: 8});
+objectsEqual(doubler({x1: -4, x2: 0}), {x1: -8, x2: 0});
+
+//console.log(Object.keys(a).reverse());