From 391f01c603e9d936fdbfd652c77532d0082b0cd1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 13:56:29 +0000
Subject: [PATCH 1/3] Initial plan


From f21a4ac3550ee23ca29f31d354b5e6b902b0e45f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 14:02:01 +0000
Subject: [PATCH 2/3] Add validation to prevent custom events with same name as
 browser events

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>
---
 .../Web.JS/src/Rendering/Events/EventTypes.ts         |  6 ++++++
 .../test/E2ETest/Tests/EventCustomArgsTest.cs         | 11 +++++++++++
 .../BasicTestApp/EventCustomArgsComponent.razor       |  9 +++++++++
 3 files changed, 26 insertions(+)

diff --git a/src/Components/Web.JS/src/Rendering/Events/EventTypes.ts b/src/Components/Web.JS/src/Rendering/Events/EventTypes.ts
index 89eb799ed3b9..e2cdef267a20 100644
--- a/src/Components/Web.JS/src/Rendering/Events/EventTypes.ts
+++ b/src/Components/Web.JS/src/Rendering/Events/EventTypes.ts
@@ -23,6 +23,12 @@ export function registerCustomEventType(eventName: string, options: EventTypeOpt
     throw new Error(`The event '${eventName}' is already registered.`);
   }
 
+  // When aliasing a browser event, the custom event name must be different from the browser event name
+  // to avoid double-triggering (once for the browser event, once for the custom event wrapper)
+  if (options.browserEventName && eventName === options.browserEventName) {
+    throw new Error(`The custom event '${eventName}' cannot have the same name as its browserEventName '${options.browserEventName}'. Choose a different name for the custom event.`);
+  }
+
   // If applicable, register this as an alias of the given browserEventName
   if (options.browserEventName) {
     const aliasGroup = browserEventNamesToAliases.get(options.browserEventName);
diff --git a/src/Components/test/E2ETest/Tests/EventCustomArgsTest.cs b/src/Components/test/E2ETest/Tests/EventCustomArgsTest.cs
index a5a236a67585..a0bafe47d750 100644
--- a/src/Components/test/E2ETest/Tests/EventCustomArgsTest.cs
+++ b/src/Components/test/E2ETest/Tests/EventCustomArgsTest.cs
@@ -170,6 +170,17 @@ public void CanRegisterCustomEventAndSupplyComplexParams()
             line => Assert.Equal("Event with IJSObjectReference received: Hello!", line));
     }
 
+    [Fact]
+    public void ThrowsErrorWhenEventNameMatchesBrowserEventName()
+    {
+        // Attempt to register a custom event with the same name as the browser event
+        Browser.Exists(By.Id("register-invalid-same-name-event")).Click();
+        
+        // Verify that an error is thrown
+        var errorMessage = Browser.Exists(By.Id("same-name-event-error")).Text;
+        Assert.Contains("cannot have the same name as its browserEventName", errorMessage);
+    }
+
     void SendKeysSequentially(IWebElement target, string text)
     {
         foreach (var c in text)
diff --git a/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor b/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
index 805cf82b9ff6..ec2f6781f573 100644
--- a/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
+++ b/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
@@ -60,6 +60,15 @@
             onclick="Blazor.registerCustomEventType('custommouseover', { browserEventName: 'mouseover' })">
         Register custom mouseover event (which has no corresponding native listener)
     </button>
+
+    <button id="register-invalid-same-name-event"
+            onclick="try { Blazor.registerCustomEventType('click', { browserEventName: 'click' }); document.getElementById('same-name-event-error').textContent = 'No error thrown'; } catch (error) { document.getElementById('same-name-event-error').textContent = error.message; }">
+        Try to register event with same name as browserEventName (should throw error)
+    </button>
+</p>
+
+<p>
+    <span id="same-name-event-error"></span>
 </p>
 
 <p>

From bee2de4e64819679ef4c48ab9c0a241252ef6006 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 14:12:23 +0000
Subject: [PATCH 3/3] Fix test to use non-pre-registered event name

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>
---
 .../test/testassets/BasicTestApp/EventCustomArgsComponent.razor | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor b/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
index ec2f6781f573..b7afb2d5d192 100644
--- a/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
+++ b/src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
@@ -62,7 +62,7 @@
     </button>
 
     <button id="register-invalid-same-name-event"
-            onclick="try { Blazor.registerCustomEventType('click', { browserEventName: 'click' }); document.getElementById('same-name-event-error').textContent = 'No error thrown'; } catch (error) { document.getElementById('same-name-event-error').textContent = error.message; }">
+            onclick="try { Blazor.registerCustomEventType('scrolltop', { browserEventName: 'scrolltop' }); document.getElementById('same-name-event-error').textContent = 'No error thrown'; } catch (error) { document.getElementById('same-name-event-error').textContent = error.message; }">
         Try to register event with same name as browserEventName (should throw error)
     </button>
 </p>