ASP.net MVC returning JSONP

Here is a simple solution, if you don't want to define an action filter

Client side code using jQuery:

  $.ajax("http://www.myserver.com/Home/JsonpCall", { dataType: "jsonp" }).done(function (result) {});

MVC controller action. Returns content result with JavaScript code executing callback function provided with query string. Also sets JavaScript MIME type for response.

 public ContentResult JsonpCall(string callback)
 {
      return Content(String.Format("{0}({1});",
          callback, 
          new JavaScriptSerializer().Serialize(new { a = 1 })),    
          "application/javascript");
 }

Rather than subclassing my controllers with Jsonp() methods, I went the extension method route as it feels a touch cleaner to me. The nice thing about the JsonpResult is that you can test it exactly the same way you would a JsonResult.

I did:

public static class JsonResultExtensions
{
    public static JsonpResult ToJsonp(this JsonResult json)
    {
        return new JsonpResult { ContentEncoding = json.ContentEncoding, ContentType = json.ContentType, Data = json.Data, JsonRequestBehavior = json.JsonRequestBehavior};
    }
}

This way you don't have to worry about creating all the different Jsonp() overloads, just convert your JsonResult to a Jsonp one.