Clientside prevent update

CHANGELOG.md

@@ -2,6 +2,13 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+### Added
+- [#964](https://github.com/plotly/dash/pull/964) Adds support for preventing
+updates in clientside functions. 
+  - Reject all updates with `throw window.dash_clientside.PreventUpdate;`
+  - Reject a single output by returning `window.dash_clientside.no_update`
+
 ## [1.4.1] - 2019-10-17
 ### Fixed
 - [#969](https://github.com/plotly/dash/pull/969) Fix warnings emitted by react devtools coming from our own devtools components.

dash-renderer/src/actions/index.js

@@ -565,6 +565,27 @@ function updateOutput(
     // Clientside hook
     if (clientside_function) {
         let returnValue;
+
+        /*
+         * Create the dash_clientside namespace if it doesn't exist and inject
+         * no_update and PreventUpdate.
+         */
+        if (!window.dash_clientside) {
+            window.dash_clientside = {};
+        }
+
+        if (!window.dash_clientside.no_update) {
+            Object.defineProperty(window.dash_clientside, 'no_update', {
+                value: {description: 'Return to prevent updating an Output.'},
+                writable: false,
+            });
+
+            Object.defineProperty(window.dash_clientside, 'PreventUpdate', {
+                value: {description: 'Throw to prevent updating all Outputs.'},
+                writable: false,
+            });
+        }
+
         try {
             returnValue = window.dash_clientside[clientside_function.namespace][
                 clientside_function.function_name
@@ -573,6 +594,14 @@ function updateOutput(
                 ...(has('state', payload) ? pluck('value', payload.state) : [])
             );
         } catch (e) {
+            /*
+             * Prevent all updates.
+             */
+            if (e === window.dash_clientside.PreventUpdate) {
+                updateRequestQueue(true, STATUS.PREVENT_UPDATE);
+                return;
+            }
+
             /* eslint-disable no-console */
             console.error(
                 `The following error occurred while executing ${clientside_function.namespace}.${clientside_function.function_name} ` +
@@ -618,6 +647,13 @@ function updateOutput(
              */
             updateRequestQueue(false, STATUS.OK);
 
+            /*
+             * Prevent update.
+             */
+            if (outputValue === window.dash_clientside.no_update) {
+                return;
+            }
+
             // Update the layout with the new result
             const appliedProps = doUpdateProps(outputId, updatedProps);
 

dash/_utils.py

@@ -128,7 +128,8 @@ def create_callback_id(output):
 
 
 def run_command_with_process(cmd):
-    proc = subprocess.Popen(shlex.split(cmd, posix=sys.platform != "win32"))
+    is_win = sys.platform == "win32"
+    proc = subprocess.Popen(shlex.split(cmd, posix=is_win), shell=is_win)
     proc.wait()
     if proc.poll() is None:
         logger.warning("🚨 trying to terminate subprocess in safe way")

dash/dependencies.py

@@ -35,6 +35,11 @@ class State(DashDependency):  # pylint: disable=too-few-public-methods
 class ClientsideFunction:
     # pylint: disable=too-few-public-methods
     def __init__(self, namespace=None, function_name=None):
+
+        if namespace in ['PreventUpdate', 'no_update']:
+            raise ValueError('"{}" is a forbidden namespace in'
+                             ' dash_clientside.'.format(namespace))
+
         self.namespace = namespace
         self.function_name = function_name
 

tests/integration/clientside/assets/clientside.js

@@ -22,6 +22,20 @@ window.dash_clientside.clientside = {
         return parseInt(value, 10) + 1;
     },
 
+    add1_prevent_at_11: function (value1, value2) {
+        if (parseInt(value1, 10) === 11) {
+            throw window.dash_clientside.PreventUpdate;
+        }
+        return parseInt(value2, 10) + 1;
+    },
+
+    add1_no_update_at_11: function (value1, value2, value3) {
+        if (parseInt(value1, 10) === 11) {
+            return [window.dash_clientside.no_update, parseInt(value3, 10) + 1];
+        }
+        return [parseInt(value2, 10) + 1, parseInt(value3, 10) + 1];
+    },
+
     add_to_four_outputs: function(value) {
         return [
             parseInt(value) + 1,

tests/integration/clientside/test_clientside.py

@@ -4,7 +4,7 @@
 import dash_html_components as html
 import dash_core_components as dcc
 from dash import Dash
-from dash.dependencies import Input, Output, ClientsideFunction
+from dash.dependencies import Input, Output, State, ClientsideFunction
 
 
 def test_clsd001_simple_clientside_serverside_callback(dash_duo):
@@ -261,3 +261,86 @@ def test_clsd005_clientside_fails_when_returning_a_promise(dash_duo):
     dash_duo.wait_for_text_to_equal("#input", "hello")
     dash_duo.wait_for_text_to_equal("#side-effect", "side effect")
     dash_duo.wait_for_text_to_equal("#output", "output")
+
+
+def test_clsd006_PreventUpdate(dash_duo):
+    app = Dash(__name__, assets_folder="assets")
+
+    app.layout = html.Div(
+        [
+            dcc.Input(id="first", value=1),
+            dcc.Input(id="second", value=1),
+            dcc.Input(id="third", value=1)
+        ]
+    )
+
+    app.clientside_callback(
+        ClientsideFunction(namespace="clientside", function_name="add1_prevent_at_11"),
+        Output("second", "value"),
+        [Input("first", "value")],
+        [State("second", "value")]
+    )
+
+    app.clientside_callback(
+        ClientsideFunction(namespace="clientside", function_name="add1_prevent_at_11"),
+        Output("third", "value"),
+        [Input("second", "value")],
+        [State("third", "value")]
+    )
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_text_to_equal("#first", '1')
+    dash_duo.wait_for_text_to_equal("#second", '2')
+    dash_duo.wait_for_text_to_equal("#third", '2')
+
+    dash_duo.find_element("#first").send_keys("1")
+
+    dash_duo.wait_for_text_to_equal("#first", '11')
+    dash_duo.wait_for_text_to_equal("#second", '2')
+    dash_duo.wait_for_text_to_equal("#third", '2')
+
+    dash_duo.find_element("#first").send_keys("1")
+
+    dash_duo.wait_for_text_to_equal("#first", '111')
+    dash_duo.wait_for_text_to_equal("#second", '3')
+    dash_duo.wait_for_text_to_equal("#third", '3')
+
+
+def test_clsd006_no_update(dash_duo):
+    app = Dash(__name__, assets_folder="assets")
+
+    app.layout = html.Div(
+        [
+            dcc.Input(id="first", value=1),
+            dcc.Input(id="second", value=1),
+            dcc.Input(id="third", value=1)
+        ]
+    )
+
+    app.clientside_callback(
+        ClientsideFunction(namespace="clientside", function_name="add1_no_update_at_11"),
+        [Output("second", "value"),
+         Output("third", "value")],
+        [Input("first", "value")],
+        [State("second", "value"),
+         State("third", "value")]
+    )
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_text_to_equal("#first", '1')
+    dash_duo.wait_for_text_to_equal("#second", '2')
+    dash_duo.wait_for_text_to_equal("#third", '2')
+
+    dash_duo.find_element("#first").send_keys("1")
+
+    dash_duo.wait_for_text_to_equal("#first", '11')
+    dash_duo.wait_for_text_to_equal("#second", '2')
+    dash_duo.wait_for_text_to_equal("#third", '3')
+
+    dash_duo.find_element("#first").send_keys("1")
+
+    dash_duo.wait_for_text_to_equal("#first", '111')
+    dash_duo.wait_for_text_to_equal("#second", '3')
+    dash_duo.wait_for_text_to_equal("#third", '4')