[Violation] Permissions policy violation: unload is not allowed in this document.

Question

[Violation] Permissions policy violation: unload is not allowed in this document.

Prathamesh Shende 551

Hello,
I am getting this error after migrating from .net 8 to .net 10 blazor web app project. server and webassembly rendermode
"[Violation] Permissions policy violation: unload is not allowed in this document." in browser console.

how to resolve this?

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AgaveJoe 31,706 Reputation points

2026-08-15T13:01:11.5866667+00:00
The unload event fires when a user navigates away from, refreshes, or closes a page. Developers traditionally used this synchronous event to clean up state or send analytical data. However, modern Chromium-based browsers (Chrome, Edge) have begun strictly restricting unload via Permissions Policy because it is synchronous, unreliable, and blocks page lifecycles like the Back/Forward cache (bfcache).

To resolve this, you need to identify where the unload handler is being registered:

Check the DevTools Console: Click the source link next to the [Violation] message in your browser console to see exactly which script or library is adding the listener.

If it is your own custom JavaScript: Move away from unload.

For saving state or cleanup, use the pagehide or visibilitychange events instead.

If you are using it as a "last gasp" to send telemetry/analytics, use navigator.sendBeacon() inside a visibilitychange listener.

If it comes from a third-party package/library: Check for an updated version of that NuGet or NPM package that removes deprecated unload listeners.

Check Browser Extensions: Test the page in an Incognito/Private window to rule out injected scripts from extensions.
Danny Nguyen (WICLOUD CORPORATION) 8,725 Reputation points Microsoft External Staff Moderator

2026-08-17T02:16:41.8833333+00:00

I'm looking into this post and will get back to you soon. Thank you for your patience.
Prathamesh Shende 551 Reputation points

2026-08-17T02:25:24.45+00:00

@AgaveJoe Sir, I have tried this same in incognito mode and also in fresh install browser. till last friday it was fine no error. But suddenly this error popup in browser console tab. But if this from js how we going to change or control code from third-party library like bootstrap or any while they may contain the unload event func.

Answer accepted by question author

0 additional answers

AgaveJoe 31,706 Reputation points

2026-08-15T13:01:11.5866667+00:00

The unload event fires when a user navigates away from, refreshes, or closes a page. Developers traditionally used this synchronous event to clean up state or send analytical data. However, modern Chromium-based browsers (Chrome, Edge) have begun strictly restricting unload via Permissions Policy because it is synchronous, unreliable, and blocks page lifecycles like the Back/Forward cache (bfcache).

To resolve this, you need to identify where the unload handler is being registered:

Check the DevTools Console: Click the source link next to the [Violation] message in your browser console to see exactly which script or library is adding the listener.

If it is your own custom JavaScript: Move away from unload.

For saving state or cleanup, use the pagehide or visibilitychange events instead.

If you are using it as a "last gasp" to send telemetry/analytics, use navigator.sendBeacon() inside a visibilitychange listener.

If it comes from a third-party package/library: Check for an updated version of that NuGet or NPM package that removes deprecated unload listeners.

Check Browser Extensions: Test the page in an Incognito/Private window to rule out injected scripts from extensions.
Danny Nguyen (WICLOUD CORPORATION) 8,725 Reputation points Microsoft External Staff Moderator

2026-08-17T02:16:41.8833333+00:00

I'm looking into this post and will get back to you soon. Thank you for your patience.
Prathamesh Shende 551 Reputation points

2026-08-17T02:25:24.45+00:00

@AgaveJoe Sir, I have tried this same in incognito mode and also in fresh install browser. till last friday it was fine no error. But suddenly this error popup in browser console tab. But if this from js how we going to change or control code from third-party library like bootstrap or any while they may contain the unload event func.

Answer 1

Hello @Prathamesh Shende ,

To address your concern regarding how to handle this when using third-party libraries: it makes sense that this error can suddenly appear, as modern Chromium-based browsers (like Chrome and Edge) are rolling out strict deprecations for the unload event across their updates to improve page performance and Back/Forward Cache capabilities.

When the unload event violation originates from a third-party library (like Bootstrap or Google Analytics) that you cannot easily modify yourself, you have a couple of options:

1. Wait for Library Updates Most major libraries (including Bootstrap) are actively removing unload listeners in newer versions because of this exact browser policy change. Upgrading your NPM/NuGet packages or updating CDN links to their latest versions is the best long-term solution.

2. Temporary Server-Side Workaround If you cannot update the library immediately and want to suppress the violation, you can explicitly grant the unload permission using the Permissions-Policy HTTP header.

You can add this middleware in your Program.cs file in your Blazor project (ensure this runs early in the pipeline):

app.Use(async (context, next) =>
{
    context.Response.Headers.Append("Permissions-Policy", "unload=*");
    await next();
});

Note: Use this workaround cautiously. Browsers are moving towards completely ignoring the unload event in the future, so relying on this header is only a temporary fix.

3. Check for specific problematic scripts You mentioned you saw this in your browser console. If you inspect the [Violation] entry in the Developer Tools (F12), there is usually a file link on the right side of the error message. Looking at that file can help you pinpoint exactly which third-party script triggers it, letting you check their GitHub issues to see if a formal fix is already released.

I hope this helps clarify how to handle third-party libraries. If you found my response helpful or informative, I would greatly appreciate it if you could follow this guidance or provide feedback.

Thank you.

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