Fixed button widget click event handler/

IPython/html/static/notebook/js/widgets/button.js

@@ -12,7 +12,8 require(["notebook/js/widget"], function(){
             this.$el = $("<button />")
                 .addClass('btn')
                 .click(function() {
-                    that.model.set('clicks', that.model.get('clicks') + 1)
+                    that.model.set('clicks', that.model.get('clicks') + 1);
+                    that.model.apply(that);
                 });
 
             this.update(); // Set defaults.

IPython/html/widgets/widget_button.py

@@ -1,3 +1,6
+import inspect
+import types
+
 from base import Widget
 from IPython.utils.traitlets import Unicode, Bool, Int
 
@@ -12,12 +15,14 class ButtonWidget(Widget):
     
     _click_handlers = []
 
-    def handle_click(self, callback, remove=False):
+
+    def on_click(self, callback, remove=False):
         if remove:
             self._click_handlers.remove(callback)
         else:
             self._click_handlers.append(callback)
 
+
     def _clicks_changed(self, name, old, new):
         if new > old:
             for handler in self._click_handlers: