I am creating a new MVC4 project, and research has lead me to believe that communicating from javascript to the server side is better achieved now through web API framework
Steven from SimpleInjector (IoC framework) advises two separate projects: What is the difference between DependencyResolver.SetResolver and HttpConfiguration.DependencyResolver in WebAPI
I tried to split the API controllers into a new project. All I've done is to create a new library project, moved the controllers inside folder named API. Then added the reference of the library project to the MVC project.
The webAPI configuration is left in the MVC project itself. It works fine.