Add support for bokeh event callbacks

holoviews/plotting/bokeh/callbacks.py

@@ -37,7 +37,7 @@ def attributes_js(attributes, handles):
         obj_name = attrs[0]
         attr_getters = ''.join(["['{attr}']".format(attr=attr)
                                 for attr in attrs[1:]])
-        if obj_name not in ['cb_obj', 'cb_data']:
+        if obj_name not in ['cb_obj', 'cb_data', 'event']:
             assign_str = '{assign}{{id: {obj_name}["id"], value: {obj_name}{attr_getters}}};\n'.format(
                 assign=data_assign, obj_name=obj_name, attr_getters=attr_getters
             )
@@ -169,6 +169,8 @@ class Callback(object):
 
     _callbacks = {}
 
+    event = False
+
     def __init__(self, plot, streams, source, **params):
         self.plot = plot
         self.streams = streams
@@ -274,6 +276,11 @@ def set_customjs(self, handle, references):
         attributes = attributes_js(self.attributes, references)
         code = 'var data = {};\n' + attributes + self.code + self_callback
 
+        if self.event:
+            js_callback = CustomJS(args=references, code=code)
+            handle.js_on_event(self.event, js_callback)
+            return
+
         # Merge callbacks if another callback has already been attached
         # otherwise set it
         if id(handle.callback) in self._callbacks: