Override Response Content-Type with OutputCache

Response content-type will be set as text/html on OutputCache is assigned, even if there is an assignment inside action.

HomeController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace WebApplication1.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        [OutputCache(Duration = 60)]
        public ActionResult NavigationScript()
        {
            Response.ContentType = "application/javascript";
            return View();
        }
    }
}

Result

Custom a attribute and change content type after output cache processed.

ResponseHeaderAttribute.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace WebApplication1.Filter
{
    public class ResponseHeaderAttribute : ActionFilterAttribute
    {
        public string ContentType { get; set; }
        public System.Text.Encoding ContentEncoding { get; set; }

        public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            if (!string.IsNullOrWhiteSpace(ContentType)) filterContext.HttpContext.Response.ContentType = ContentType;
            if (ContentEncoding != null) filterContext.HttpContext.Response.ContentEncoding = ContentEncoding;
        }
    }
}

HomeController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using WebApplication1.Filter;

namespace WebApplication1.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        [OutputCache(Duration = 60, Order = 1)]
        [ResponseHeader(ContentType = "application/javascript", Order = 2)]
        public ActionResult NavigationScript()
        {
            return View();
        }
    }
}

Result