Address @minrk 's review comments.

IPython/html/static/widgets/js/widget.js

@@ -76,7 +76,7 b' define(["widgets/js/manager",'
                     this.set_state(msg.content.data.state);
                     if (this.init_state_callback) {
                         this.init_state_callback.apply(this, [this]);
-                        this.init_state_callback = null;
+                        delete this.init_state_callback;
                     }
                     break;
                 case 'custom':

IPython/html/widgets/widget.py

@@ -102,7 +102,7 b' class Widget(LoggingConfigurable):'
         target_name = msg['content']['data']['target_name']
         widget_class = import_item(target_name)
         widget = widget_class(open_comm=False)
-        widget.set_comm(comm)
+        widget.comm = comm
 
 
     #-------------------------------------------------------------------------
@@ -160,11 +160,11 b' class Widget(LoggingConfigurable):'
                               'model_module': self._model_module})
             if self._model_id is not None:
                 args['comm_id'] = self._model_id
-            self.set_comm(Comm(**args))
+            self.comm = Comm(**args)
 
-    def set_comm(self, comm):
-        """Set's the comm of the widget."""
-        self.comm = comm
+    def _comm_changed(self, name, new):
+        """Called when the comm is changed."""
+        self.comm = new
         self._model_id = self.model_id
         
         self.comm.on_msg(self._handle_msg)
@@ -173,7 +173,6 b' class Widget(LoggingConfigurable):'
         # first update
         self.send_state()
 
-
     @property
     def model_id(self):
         """Gets the model id of this widget.