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Throw error when custom event name matches browserEventName to prevent double-triggering #64774

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Throw error when custom event name matches browserEventName to prevent double-triggering #64774

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391f01c
Initial plan
Copilot Dec 15, 2025
f21a4ac
Add validation to prevent custom events with same name as browser events
Copilot Dec 15, 2025
bee2de4
Fix test to use non-pre-registered event name
Copilot Dec 15, 2025
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6 changes: 6 additions & 0 deletions src/Components/Web.JS/src/Rendering/Events/EventTypes.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
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11 changes: 11 additions & 0 deletions src/Components/test/E2ETest/Tests/EventCustomArgsTest.cs
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Expand Up @@ -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)
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9 changes: 9 additions & 0 deletions src/Components/test/testassets/BasicTestApp/EventCustomArgsComponent.razor
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Expand Up @@ -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('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>

<p>
<span id="same-name-event-error"></span>
</p>

<p>
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