Many years ago I remember using a similar shim on ASP.NET where you'd simply decorate a server-side C# method and you could call it from JS like any other method. Not quite the way done here, but it had similar goals to blend server and client. So far, these things don't work in practice because of the so many things that differ between a browser and server environment.
https://docs.microsoft.com/en-us/dotnet/api/system.web.scrip...