Fix clientside no outputs

CHANGELOG.md

@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#2854](https://github.com/plotly/dash/pull/2854) Fix dcc.Dropdown resetting empty values to null and triggering callbacks. Fixes [#2850](https://github.com/plotly/dash/issues/2850)
 - [#2859](https://github.com/plotly/dash/pull/2859) Fix base patch operators. fixes [#2855](https://github.com/plotly/dash/issues/2855)
 - [#2856](https://github.com/plotly/dash/pull/2856) Fix multiple consecutive calls with same id to set_props only keeping the last props. Fixes [#2852](https://github.com/plotly/dash/issues/2852)
+- [#2867](https://github.com/plotly/dash/pull/2867) Fix clientside no output callback. Fixes [#2866](https://github.com/plotly/dash/issues/2866)
 
 ## [2.17.0] - 2024-05-03
 

dash/_callback.py

@@ -549,6 +549,7 @@ def register_clientside_callback(
     **kwargs,
 ):
     output, inputs, state, prevent_initial_call = handle_callback_args(args, kwargs)
+    no_output = isinstance(output, (list,)) and len(output) == 0
     insert_callback(
         callback_list,
         callback_map,
@@ -559,6 +560,7 @@ def register_clientside_callback(
         state,
         None,
         prevent_initial_call,
+        no_output=no_output,
     )
 
     # If JS source is explicitly given, create a namespace and function

dash/dash-renderer/src/actions/callbacks.ts

@@ -278,16 +278,18 @@ async function handleClientside(
             returnValue = await returnValue;
         }
 
-        zipIfArray(outputs, returnValue).forEach(([outi, reti]) => {
-            zipIfArray(outi, reti).forEach(([outij, retij]) => {
-                const {id, property} = outij;
-                const idStr = stringifyId(id);
-                const dataForId = (result[idStr] = result[idStr] || {});
-                if (retij !== dc.no_update) {
-                    dataForId[cleanOutputProp(property)] = retij;
-                }
+        if (outputs) {
+            zipIfArray(outputs, returnValue).forEach(([outi, reti]) => {
+                zipIfArray(outi, reti).forEach(([outij, retij]) => {
+                    const {id, property} = outij;
+                    const idStr = stringifyId(id);
+                    const dataForId = (result[idStr] = result[idStr] || {});
+                    if (retij !== dc.no_update) {
+                        dataForId[cleanOutputProp(property)] = retij;
+                    }
+                });
             });
-        });
+        }
     } catch (e) {
         if (e === dc.PreventUpdate) {
             status = STATUS.PREVENT_UPDATE;

tests/integration/callbacks/test_arbitrary_callbacks.py

@@ -1,7 +1,15 @@
 import time
 from multiprocessing import Value
 
-from dash import Dash, Input, Output, html, set_props, register_page
+from dash import (
+    Dash,
+    Input,
+    Output,
+    html,
+    set_props,
+    register_page,
+    clientside_callback,
+)
 
 
 def test_arb001_global_set_props(dash_duo):
@@ -188,3 +196,39 @@ def on_click(_):
     dash_duo.wait_for_style_to_equal(
         "#output", "background-color", "rgba(255, 0, 0, 1)"
     )
+
+
+def test_arb007_clientside_no_output(dash_duo):
+    app = Dash()
+
+    app.layout = [
+        html.Button("start", id="start1"),
+        html.Button("start2", id="start2"),
+        html.Div(id="output"),
+    ]
+
+    clientside_callback(
+        """
+        function(_) {
+            dash_clientside.set_props('output', {children: 'start1'})
+        }
+        """,
+        Input("start1", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    clientside_callback(
+        """
+        function(_) {
+            dash_clientside.set_props('output', {children: 'start2'})
+        }
+        """,
+        Input("start2", "n_clicks"),
+        prevent_initial_call=True,
+    )
+
+    dash_duo.start_server(app)
+
+    dash_duo.find_element("#start1").click()
+    dash_duo.wait_for_text_to_equal("#output", "start1")
+    dash_duo.find_element("#start2").click()
+    dash_duo.wait_for_text_to_equal("#output", "start2")