From 90fa4c36c51960ace9486438878cd2d6fea38650 Mon Sep 17 00:00:00 2001
From: CNFeffery <fefferypzy@gmail.com>
Date: Tue, 26 Aug 2025 10:58:01 +0800
Subject: [PATCH 1/3] Fix #3366

---
 dash/dash-renderer/src/actions/callbacks.ts   | 12 ++++-
 ...multiple_output_return_single_no_update.py | 46 +++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 tests/integration/clientside/test_clientside_multiple_output_return_single_no_update.py

diff --git a/dash/dash-renderer/src/actions/callbacks.ts b/dash/dash-renderer/src/actions/callbacks.ts
index 78b2ad1550..8f3c4f97fd 100644
--- a/dash/dash-renderer/src/actions/callbacks.ts
+++ b/dash/dash-renderer/src/actions/callbacks.ts
@@ -226,8 +226,16 @@ function refErr(errors: any, paths: any) {
 const getVals = (input: any) =>
     Array.isArray(input) ? pluck('value', input) : input.value;
 
-const zipIfArray = (a: any, b: any) =>
-    Array.isArray(a) ? zip(a, b) : [[a, b]];
+const zipIfArray = (a: any, b: any) => {
+    if (Array.isArray(a)) {
+        // For client-side callbacks with multiple Outputs, only return a single dash_clientside.no_update
+        if (b?.description === 'Return to prevent updating an Output.') {
+            return zip(a, [b]);
+        }
+        return zip(a, b);
+    }
+    return [[a, b]];
+};
 
 function cleanOutputProp(property: string) {
     return property.split('@')[0];
diff --git a/tests/integration/clientside/test_clientside_multiple_output_return_single_no_update.py b/tests/integration/clientside/test_clientside_multiple_output_return_single_no_update.py
new file mode 100644
index 0000000000..4ba55a2c40
--- /dev/null
+++ b/tests/integration/clientside/test_clientside_multiple_output_return_single_no_update.py
@@ -0,0 +1,46 @@
+from dash import (
+    Dash,
+    Input,
+    Output,
+    html,
+    clientside_callback,
+)
+
+
+def test_cmorsnu001_clientside_multiple_output_return_single_no_update(dash_duo):
+    app = Dash(__name__)
+    app.layout = html.Div(
+        [
+            html.Button("trigger", id="trigger-demo"),
+            html.Div("demo1", id="output-demo1"),
+            html.Div("demo2", id="output-demo2"),
+        ],
+        style={"padding": 50},
+    )
+
+    clientside_callback(
+        """(n_clicks) => {
+            try {
+                return window.dash_clientside.no_update;
+            } catch (e) {
+                return [null, null];
+            }
+        }""",
+        Output("output-demo1", "children"),
+        Output("output-demo2", "children"),
+        Input("trigger-demo", "n_clicks"),
+        prevent_initial_call=True,
+    )
+
+    dash_duo.start_server(app)
+
+    trigger_clicker = dash_duo.wait_for_element("#trigger-demo")
+    trigger_clicker.click()
+    dash_duo.wait_for_text_to_equal(
+        "#output-demo1",
+        "demo1",
+    )
+    dash_duo.wait_for_text_to_equal(
+        "#output-demo2",
+        "demo2",
+    )

From d339423388771f2889e137bac7ce6770db77ed03 Mon Sep 17 00:00:00 2001
From: CNFeffery <fefferypzy@gmail.com>
Date: Tue, 26 Aug 2025 11:07:50 +0800
Subject: [PATCH 2/3] Update CHANGELOG.md

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d9bc7db83b..252898131b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## Fixed
 - [#3395](https://github.com/plotly/dash/pull/3395) Fix Components added through set_props() cannot trigger related callback functions. Fix [#3316](https://github.com/plotly/dash/issues/3316)
 - [#3397](https://github.com/plotly/dash/pull/3397) Add optional callbacks, suppressing callback warning for missing component ids for a single callback.
+- [#3415](https://github.com/plotly/dash/pull/3415) Fix the error triggered when only a single no_update is returned for client-side callback functions with multiple Outputs. Fix [#3366](https://github.com/plotly/dash/issues/3366)
 
 ## [3.2.0] - 2025-07-31
 

From ae473a6ad7a0b109b78e094ace777e05d3d234c1 Mon Sep 17 00:00:00 2001
From: CNFeffery <fefferypzy@gmail.com>
Date: Tue, 26 Aug 2025 21:18:47 +0800
Subject: [PATCH 3/3] Update the judgment conditions for no_update

---
 dash/dash-renderer/src/actions/callbacks.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dash/dash-renderer/src/actions/callbacks.ts b/dash/dash-renderer/src/actions/callbacks.ts
index 8f3c4f97fd..ff677fee94 100644
--- a/dash/dash-renderer/src/actions/callbacks.ts
+++ b/dash/dash-renderer/src/actions/callbacks.ts
@@ -229,7 +229,7 @@ const getVals = (input: any) =>
 const zipIfArray = (a: any, b: any) => {
     if (Array.isArray(a)) {
         // For client-side callbacks with multiple Outputs, only return a single dash_clientside.no_update
-        if (b?.description === 'Return to prevent updating an Output.') {
+        if (b === (window as any).dash_clientside.no_update) {
             return zip(a, [b]);
         }
         return zip(a, b);