Blazor: Prerendered HeadContent gets replaced on WASM startup even if it is not changed

[hakenr]

As the WebAssembly application in browser activates it replaces server-prerendered HeadOutlet content with new (same) content (probably new instances of the DOM objects). Which causes UI flickering if you use HeadContent for injecting CSS links (e.g. to support theme switching).

Expected Behavior

Similar to rendering of regular components, the HeadOutlet should not replace the content if it did not change (in comparison to the server prerendered version).

Steps To Reproduce

Blazor WebAssemblyPrerendered mode (ASP.NET Core Host, server prerendering, ...).
Put a component in MainLayout.razor with some content.
When you start the application, the HeadOutlet prerendered content contains the content from HeadContent (correct).
But as the WebAssembly application in browser activates it replaces the HeadOutlet content with new (same) content (probably new instances of the DOM objects).
Which causes UI flickering if you use HeadContent for injecting CSS links (e.g. to support theme switching).

repro repo: https://github.com/hakenr/BlazorHeadContentPrerenderingFlicker
repro site: https://blazorheadcontentprerenderingflicker.azurewebsites.net/

.NET Version

6.0.6

[javiercn]

@hakenr thanks for contacting us.

I believe this happens because as you mention, we replace the entire contents of the DOM after prerendering.

I have filed a separate issue here to provide more context on other areas where this behavior is problematic as well as some ideas on how we can improve this area.

We are going to use the other issue to track improvements in this space, so I'm going to close this issue and I would suggest you go and upvote the issue referenced here so that we can gather customer interest on it.

[ghost]

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