A possibly naive way to write less code when you want a Controller POST action to play nicely with both vanilla and Ajax form submits.

ControllerHelper.cs

    public static class ControllerHelper {

        // working with forms on MVC 3, I found a handful of instances where I wanted to support ajax form submits using the jQuery form plugin
        // but still wanted to keep the option of graceful degradation if javascript wasn't supported.
        // there might be a better approach to this, like having seperate Ajax and vanilla Post methods,
        // moving the logic that currently resides in the controller elsewhere. That would increase complexity a lot all at once.
        // Perhaps this kind of thing is the right path in the short term.
        public static ActionResult PartialIfAjax_ViewOtherwise(this Controller controller, string viewName, object model) {
            if (controller.Request.IsAjaxRequest()) {
                return controller.PartialView(viewName, model);
            }
            return controller.View(viewName: viewName, model: model);
        }
    }

Works for MVC 5 ?