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JSONP in ASP.NET Web API Quick Get Started

, 4 Aug 2013 CPOL
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This tip contains the basic introduction to the JSONP, Same-Origin and Cross-Origin Resource Sharing concepts and quick get started with JSONP in ASP.NET Web API.


While searching the web to get started with JSONP in ASP.NET Web API, I was not able to find a real quick start guide. Rather, I found many discussions and detailed articles. So I thought of collating the information from across the web to provide a real simple quick start guide on JSONP in ASP.NET Web API for beginners.


This is a quick get started with JavaScript Object Notation with Padding (JSONP) in ASP.NET Web API to get data from different domains and also explain about the JSONP, Same-Origin and Cross-Origin Resource Sharing concepts.

Same-Origin Policy Vs. Cross-Origin Resource Sharing (CORS)

Same-origin policy is a concept in browser-side programming languages (such as JavaScript) which allows accessing resources in the same site (same domain) but preventing accessing resources in different domains.

Cross-origin resource sharing (CORS) is a mechanism that allows JavaScript on a web page to make XMLHttpRequests to another domain, not the domain the JavaScript originated from. Such "cross-domain" requests would otherwise be forbidden by web browsers, per the same origin security policy. CORS defines a way in which the browser and the server can interact to determine whether or not to allow the cross-origin request.

What and Why JSONP?

AJAX (XMLHttpRequest) doesn’t allow cross domain communication due to security reasons. JavaScript Object Notation with Padding (JSONP) is a way to grab JSON data from external domains. It’s a better and cleaner alternative to other approaches (web proxy and IFrame) to get data from an external domain / CORS (Cross-Origin Resource Sharing).


JSONP (JavaScript Object Notation with Padding) = JSON data padded with JavaScript function name

callbackFunc({ "firstName": "Sathik Ali", "lastName": "S" }); 

Enable AJAX Request to Get JSONP Data

We need to set callback and data type attributes of Ajax request as highlighted below:

<script type="text/javascript">
$("#getJsonp").click(function () {
       	type: 'GET',
              url: "http://localhost:5511/api/values/GetUserName/1",
              callback: 'callbackFunc',
              contentType: "application/json",
              dataType: 'jsonp'
function callbackFunc(resultData) {

Enable ASP.NET Web API to Return JSONP Data

  1. Install the JSONP MediaTypeFormatter by entering the following command using NuGet Package Manager console in Visual Studio.
    Install-Package WebApiContrib.Formatting.Jsonp
  2. Add a FormatterConfig class in App_Start folder:
        public class FormatterConfig
            public static void RegisterFormatters(MediaTypeFormatterCollection formatters)
                var jsonFormatter = formatters.JsonFormatter;
                jsonFormatter.SerializerSettings = new JsonSerializerSettings
                    ContractResolver = new CamelCasePropertyNamesContractResolver()
                // Insert the JSONP formatter in front of the standard JSON formatter.
                var jsonpFormatter = new JsonpMediaTypeFormatter(formatters.JsonFormatter);
                formatters.Insert(0, jsonpFormatter);
  3. Add the following routes in /App_Start/RouteConfig.cs:
                    name: "DefaultApi",
                    routeTemplate: "api/{controller}/{id}/{format}",
                    defaults: new { id = RouteParameter.Optional, format = RouteParameter.Optional }
  4. Add the following line in the Application_Start method of Global.ascx.cs:

Points of Interest

If you want your routes mapping with action, please specify the following in App_Start/RouteConfig.cs:

                name: "DefaultApi",
                routeTemplate: "api/{controller}/{action}/{id}/{format}",
                defaults: new { id = RouteParameter.Optional, format = RouteParameter.Optional }



This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

S.Sathik Ali
Technical Lead
India India
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Comments and Discussions

GeneralMy vote of 5 PinmemberMember 1071222928-Feb-15 9:13 
SuggestionFix for 'System.Web.Http.GlobalConfiguration.get_Configuration()' error PinmemberRudy Otzen7-Jan-15 0:39 
GeneralRe: Fix for 'System.Web.Http.GlobalConfiguration.get_Configuration()' error PinmemberS.Sathik Ali8-Jan-15 3:03 
GeneralMy vote of 5 Pinmemberfmtoro25-Jun-14 10:24 
GeneralRe: My vote of 5 PinmemberS.Sathik Ali26-Jun-14 20:59 
QuestionOnce again Pinmemberfmtoro25-Jun-14 10:22 
QuestionMost valuable article Pinmembersoftsathian21-Apr-14 19:34 
AnswerRe: Most valuable article PinmemberS.Sathik Ali23-Apr-14 18:45 
QuestionAwesome article Pinmembercodeprojecthai2-Mar-14 13:07 
GeneralMy vote of 5 Pinmembermanoj.jsm5-Aug-13 0:29 
GeneralRe: My vote of 5 PinprofessionalS.Sathik Ali5-Aug-13 9:14 

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