Add preventDefault and stopPropagation to event spec

.gitignore

@@ -20,6 +20,7 @@ parts/
 sdist/
 var/
 wheels/
+pip-wheel-metadata
 *.egg-info/
 .installed.cfg
 *.egg

docs/event-spec.md

@@ -50,7 +50,11 @@ vdom will:
 
 ```python
 {
-    'event_type': '{hash}_{target_name}'
+    '{eventName}': {
+        'hash': string,
+        'stopPropagation': boolean,
+        'preventDefault': boolean
+    }
 }
 ```
 

vdom/core.py

@@ -46,30 +46,6 @@ def escape(s):
 _validate_err_template = "Your object didn't match the schema: {}. \n {}"
 
 
-def create_event_handler(event_type, handler):
-    """Register a comm and return a serializable object with target name"""
-
-    target_name = '{hash}_{event_type}'.format(hash=hash(handler), event_type=event_type)
-
-    def handle_comm_opened(comm, msg):
-        @comm.on_msg
-        def _handle_msg(msg):
-            data = msg['content']['data']
-            event = json.loads(data)
-            return_value = handler(event)
-            if return_value:
-                comm.send(return_value)
-
-        comm.send('Comm target "{target_name}" registered by vdom'.format(target_name=target_name))
-
-    # Register a new comm for this event handler
-    if get_ipython():
-        get_ipython().kernel.comm_manager.register_target(target_name, handle_comm_opened)
-
-    # Return a serialized object
-    return target_name
-
-
 def to_json(el, schema=None):
     """Convert an element to VDOM JSON
 
@@ -102,6 +78,69 @@ def to_json(el, schema=None):
     return json_el
 
 
+def eventHandler(handler=None, preventDefault=False, stopPropagation=False):
+    """Create an event handler with special attributes
+
+    Typically when defining event handlers you can simply pass them to a VDOM Component,
+    however you can't prevent the event's default behaviors or stop its propagation up
+    through the DOM this way.
+
+    Parameters:
+        preventDefault: stop the event's default behavior
+        stopPropagation: halt the event's propagation up the DOM
+
+    Examples:
+        >>> @eventHandler(preventDefault=True, stopPropagation=True)
+        ... def on_hover(event):
+                pass
+        >>> drag_drop_spot = VDOM("div", event_handler={"onDragOver": hover})
+    """
+
+    def setup(handler):
+        return EventHandler(handler, preventDefault, stopPropagation)
+
+    if handler is not None:
+        return setup(handler)
+    else:
+        return setup
+
+
+class EventHandler(object):
+
+    def __init__(self, handler, prevent_default=False, stop_propagation=False):
+        self._handler = handler
+        self._prevent_default = prevent_default
+        self._stop_propagation = stop_propagation
+        # Register a new comm for this event handler
+        if get_ipython():
+            comm_manager = get_ipython().kernel.comm_manager
+            comm_manager.register_target(hash(self), self._on_comm_opened)
+
+    def serialize(self):
+        return {
+            "hash": hash(self),
+            "preventDefault": self._prevent_default,
+            "stopPropagation": self._stop_propagation,
+        }
+
+    def __call__(self, event):
+        return self._handler(event)
+
+    def __hash__(self):
+        return hash(self._handler)
+
+    def _on_comm_opened(self, comm, msg):
+        comm.on_msg(self._on_comm_msg)
+        comm.send('Comm target "{hash}" registered by vdom'.format(hash=hash(self)))
+
+    def _on_comm_msg(self, msg):
+        data = msg['content']['data']
+        event = json.loads(data)
+        return_value = self(event)
+        if return_value:
+            comm.send(return_value)
+
+
 class VDOM(object):
     """A basic virtual DOM class which allows you to write literal VDOM spec
 
@@ -191,9 +230,10 @@ def to_dict(self):
         vdom_dict = {'tagName': self.tag_name, 'attributes': attributes}
         if self.event_handlers:
             event_handlers = dict(self.event_handlers.items())
-            for key, value in event_handlers.items():
-                value = create_event_handler(key, value)
-                event_handlers[key] = value
+            for key, handler in event_handlers.items():
+                if not isinstance(handler, EventHandler):
+                    handler = EventHandler(handler)
+                event_handlers[key] = handler.serialize()
             vdom_dict['eventHandlers'] = event_handlers
         if self.key:
             vdom_dict['key'] = self.key

vdom/tests/test_core.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-from ..core import create_component, create_element, to_json, VDOM, convert_style_key
+from ..core import create_component, create_element, to_json, VDOM, convert_style_key, eventHandler
 from ..helpers import div, p, img, h1, b, button
 from jsonschema import ValidationError, validate
 import os
@@ -68,7 +68,7 @@ def test_css():
     }
 
 
-def test_event_handler():
+def test_event_handler_normal_function():
     def handle_click(event):
         print(event)
 
@@ -77,7 +77,41 @@ def handle_click(event):
     assert el.to_html() == '<button>click me</button>'
     assert el.to_dict() == {
         'attributes': {},
-        'eventHandlers': {'onClick': '{hash}_onClick'.format(hash=hash(handle_click))},
+        'eventHandlers': {
+            'onClick': {
+                'hash': hash(handle_click),
+                'stopPropagation': False,
+                'preventDefault': False,
+            },
+        },
+        'children': ['click me'],
+        'tagName': 'button',
+    }
+
+
+def test_event_handler_decorator():
+
+    @eventHandler(stopPropagation=True, preventDefault=True)
+    def handle_click(event):
+        pass
+
+    assert handle_click.serialize() == {
+        "hash": hash(handle_click._handler),
+        "preventDefault": True,
+        "stopPropagation": True,
+    }
+
+    el = button('click me', onClick=handle_click)
+
+    assert el.to_dict() == {
+        'attributes': {},
+        'eventHandlers': {
+            'onClick': {
+                'hash': hash(handle_click),
+                'stopPropagation': True,
+                'preventDefault': True,
+            },
+        },
         'children': ['click me'],
         'tagName': 'button',
     }
@@ -199,13 +233,13 @@ def test_create_element_deprecated():
 
 def test_component_disallows_children():
     void = create_component('void', allow_children=False)
-    with pytest.raises(ValueError, message='<void /> cannot have children'):
+    with pytest.raises(ValueError, match='<void /> cannot have children'):
         void(div())
 
 
 def test_component_disallows_children_kwargs():
     void = create_component('void', allow_children=False)
-    with pytest.raises(ValueError, message='<void /> cannot have children'):
+    with pytest.raises(ValueError, match='<void /> cannot have children'):
         void(children=div())