From 79f8c24e9f055c9cb6572f20014d67b670ba14fb Mon Sep 17 00:00:00 2001
From: Chris P <chris@plot.ly>
Date: Sat, 30 Mar 2019 13:13:26 -0400
Subject: [PATCH] :racehorse: clientside callback interface

see associated PR & examples in
https://github.com/plotly/dash-renderer/pull/143
---
 dash/dash.py         | 13 +++++++++++--
 dash/dependencies.py | 13 +++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 040152f29b..ed1460fab2 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -631,6 +631,7 @@ def dependencies(self):
                 'output': k,
                 'inputs': v['inputs'],
                 'state': v['state'],
+                'client_function': v['client_function']
             } for k, v in self.callback_map.items()
         ])
 
@@ -946,7 +947,7 @@ def _validate_value(val, index=None):
     # TODO - Check this map for recursive or other ill-defined non-tree
     # relationships
     # pylint: disable=dangerous-default-value
-    def callback(self, output, inputs=[], state=[]):
+    def callback(self, output, inputs=[], state=[], client_function=None):
         self._validate_callback(output, inputs, state)
 
         callback_id = _create_callback_id(output)
@@ -960,8 +961,16 @@ def callback(self, output, inputs=[], state=[]):
             'state': [
                 {'id': c.component_id, 'property': c.component_property}
                 for c in state
-            ]
+            ],
         }
+        if client_function is not None:
+            self.callback_map[callback_id]['client_function'] = {
+                'namespace': client_function.namespace,
+                'function_name': client_function.function_name
+            }
+        else:
+            self.callback_map[callback_id]['client_function'] = {}
+
 
         def wrap_func(func):
             @wraps(func)
diff --git a/dash/dependencies.py b/dash/dependencies.py
index 3f946f1ebf..1e7985c4cc 100644
--- a/dash/dependencies.py
+++ b/dash/dependencies.py
@@ -32,3 +32,16 @@ class Input(DashDependency):
 # pylint: disable=too-few-public-methods
 class State(DashDependency):
     """Use the value of a state in a callback but don't trigger updates."""
+
+
+# pylint: disable=too-few-public-methods
+class ClientFunction:
+    def __init__(self, namespace=None, function_name=None):
+        self.namespace = namespace
+        self.function_name = function_name
+
+    def __repr__(self):
+        return 'ClientFunction({}, {})'.format(
+            self.namespace,
+            self.function_name
+        )