Simplify callback handler definition for classic notebook.

Author: jasongrout

widgetsnbextension/src/manager.js

@@ -289,36 +289,17 @@ WidgetManager.prototype._get_connected_kernel = function() {
     });
 };
 
+/**
+ * Callback handlers for a specific view
+ */
 WidgetManager.prototype.callbacks = function (view) {
-    /**
-     * callback handlers specific a view
-     */
-    var callbacks = {};
+    var callbacks = widgets.ManagerBase.prototype.callbacks.call(this, view);
     if (view && view.options.output) {
-        // Try to get output handlers
         var output = view.options.output;
-        var handle_output = null;
-        var handle_clear_output = null;
-        if (output) {
-            handle_output = _.bind(output.handle_output, output);
-            handle_clear_output = _.bind(output.handle_clear_output, output);
+        callbacks.iopub = {
+            output: output.handle_output.bind(output),
+            clear_output: output.handle_clear_output.bind(output)
         }
-
-        // Create callback dictionary using what is known
-        var that = this;
-        callbacks = {
-            iopub : {
-                output : handle_output,
-                clear_output : handle_clear_output,
-
-                // Special function only registered by widget messages.
-                // Allows us to get the cell for a message so we know
-                // where to add widgets if the code requires it.
-                get_cell : function () {
-                    return cell;
-                },
-            },
-        };
     }
     return callbacks;
 };