automatically copy static files like css or js from a Blazor component lib into the app's wwwroot

One thing in this library would be the reuse of the javascript alert() method. I know how to do this, this involves adding this in a .cshtml page:

<script>
  Blazor.registerFunction('Alert', (message) => {
      alert(message);
  });
</script>

and this in my code:

public void Alert(string message)
{
     RegisteredFunction.Invoke<object>("Alert", message);
}

I ended up with creating my own blazor component containing my javascript, like this:

public class BlazorExtensionScripts : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
{

    protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
    {
        builder.OpenElement(0, "script");
        builder.AddContent(1, "Blazor.registerFunction('Alert', (message) => { alert(message); });");
        builder.CloseElement();
    }
}

And adding it to my app.cshtml like this:

@addTagHelper *, BlazorExtensions

<Router AppAssembly=typeof(Program).Assembly />

<BlazorExtensionScripts></BlazorExtensionScripts>

By default, publishing a Blazor WebAssembly app places the app's static assets, including Blazor framework files (_framework folder assets), at the root path (/) in published output. The <StaticWebAssetBasePath> property specified in the project file (.csproj) sets the base path to a non-root path:

<PropertyGroup>
  <StaticWebAssetBasePath>{PATH}</StaticWebAssetBasePath>
</PropertyGroup>

In the Client app's project file (.csproj) or the standalone Blazor WebAssembly app's project file (.csproj):

<PropertyGroup>
  <StaticWebAssetBasePath>app1</StaticWebAssetBasePath>
</PropertyGroup>

Configure options through dependency injection (DI) in Program.cs using StaticFileOptions:

using Microsoft.AspNetCore.StaticFiles;

...

var provider = new FileExtensionContentTypeProvider();
provider.Mappings["{EXTENSION}"] = "{CONTENT TYPE}";

builder.Services.Configure<StaticFileOptions>(options =>
{
    options.ContentTypeProvider = provider;
});

Configure the custom file provider in the first call with StaticFileOptions. The second middleware serves blazor.server.js, which uses the default static files configuration provided by the Blazor framework.

using Microsoft.AspNetCore.StaticFiles;

...

var provider = new FileExtensionContentTypeProvider();
provider.Mappings["{EXTENSION}"] = "{CONTENT TYPE}";

app.UseStaticFiles(new StaticFileOptions { ContentTypeProvider = provider });
app.UseStaticFiles();

You can avoid interfering with serving _framework/blazor.server.js by using MapWhen to execute a custom Static File Middleware:

app.MapWhen(ctx => !ctx.Request.Path
    .StartsWithSegments("/_framework/blazor.server.js"),
        subApp => subApp.UseStaticFiles(new StaticFileOptions() { ... }));