Lazy loaded `BlazorCustomElements.js` file does not adhere to the `loadBootResource` configuration

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Hi guys,

Since .NET 7 is out, I’ve been test driving Blazor WASM to see how to use it in combination with other frameworks.

I’ve configured the following to be able to point the loading of resources to a specific server. https://learn.microsoft.com/en-us/aspnet/core/blazor/fundamentals/startup?view=aspnetcore-7.0#load-boot-resources

Which works nicely.

I’m now using the Microsoft.AspNetCore.Components.CustomElements nuget package to get CustomElements to work. Initially you had to reference the script manually:

<script src="_content/Microsoft.AspNetCore.Components.CustomElements/BlazorCustomElements.js"></script>

But since .NET 7 has been released it’s lazy loaded by ASP.NET. Which is awesome. The only problem is: it uses the URL of the server you are on, to lazy load the file, while it should be respecting the loadBootResource configuration.

Which is a problem for me, as I’m depending on the loadBootResource function to get the WASM files from another server, for example a CDN.

Is that something you guys can fix?

cc: @guardrex https://github.com/dotnet/AspNetCore.Docs/issues/27638

Expected Behavior

Loading the JS for CustomElements should respect the loadBootResource configuration.

Steps To Reproduce

1. Create a Blazor WASM client app
2. Create a simple webserver that loads the Blazor script with autostart="false" and add the following bootstrapping lines:

Blazor.start({
        loadBootResource: function (type, name, defaultUri, integrity) {
          return 'https://localhost:8088/' + defaultUri`;
        }
      });

1. Install the CustomElements nuget and implement a basic customelement.
2. Try loading the basic webserver with the customelement and blazor script.

Exceptions (if any)

No response

.NET Version

7

Anything else?

No response

[SteveSandersonMS]

I’ve filed an issue describing this as a general feature request: https://github.com/dotnet/aspnetcore/issues/45148

A more practical solution for you in the short term would be to implement a service worker that will let you override how all static resources are fetched.

[martinlingstuyl]

Thanks!