React SPA Net Core

YourApp.csproj

<PropertyGroup>
        <TargetFramework>netcoreapp3.1</TargetFramework>
        <SpaRoot>frontend\</SpaRoot>
        <DefaultItemExcludes>$(DefaultItemExcludes);$(SpaRoot)node_modules\**</DefaultItemExcludes>
</PropertyGroup>

<ItemGroup>
    <None Update="app.db" CopyToOutputDirectory="PreserveNewest" ExcludeFromSingleFile="true"/>
</ItemGroup>
<ItemGroup>
    <!-- Don't publish the SPA source files, but do show them in the project files list -->
    <Content Remove="$(SpaRoot)**"/>
    <None Remove="$(SpaRoot)**"/>
    <None Include="$(SpaRoot)**" Exclude="$(SpaRoot)node_modules\**"/>
</ItemGroup>

<Target Name="PublishRunWebpack" AfterTargets="ComputeFilesToPublish">
      <!-- As part of publishing, ensure the JS resources are freshly built in production mode -->
      <!-- Customize these command as needed -->
      <Exec WorkingDirectory="$(SpaRoot)" Command="yarn"/>
      <Exec WorkingDirectory="$(SpaRoot)" Command="yarn build"/>

      <!-- Include the newly-built files in the publish output -->
      <ItemGroup>
          <DistFiles Include="$(SpaRoot)build\**"/>
          <ResolvedFileToPublish Include="@(DistFiles->'%(FullPath)')" Exclude="@(ResolvedFileToPublish)">
              <RelativePath>%(DistFiles.Identity)</RelativePath>
              <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
              <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
          </ResolvedFileToPublish>
      </ItemGroup>
  </Target>