Let bind(x) return object

Change-Id: Ic597c75fa9695c5f8de13c20f8e141cbfa047920
diff --git a/dev/js/spec/buttongroupSpec.js b/dev/js/spec/buttongroupSpec.js
index 67baaef..a25d15c 100644
--- a/dev/js/spec/buttongroupSpec.js
+++ b/dev/js/spec/buttongroupSpec.js
@@ -92,7 +92,9 @@
       expect(fun.count).toEqual(0);
 
       // Bind group to another object
-      group.bind(fun);
+      var group2 = group.bind(fun);
+      expect(group2).toEqual(group);
+      expect(group.bind()).toEqual(fun);
 
       group.add('Incr', undefined, function (e) {
         // increment on bind object
diff --git a/dev/js/src/buttongroup.js b/dev/js/src/buttongroup.js
index 443d650..cb6a95c 100644
--- a/dev/js/src/buttongroup.js
+++ b/dev/js/src/buttongroup.js
@@ -98,6 +98,7 @@
     bind : function (obj) {
       if (obj !== undefined) {
         this._bind = obj;
+        return this;
       };
       return this._bind || this;
     },