Return JSON from ASMX web service, without XML wrapper?

Use this:

var JsonString = ....;
$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: "YourWebServiceName.asmx/yourmethodname",
    data: "{'TheData':'" + JsonString + "'}",
    dataType: "json",
    success: function (msg) {
        var data = msg.hasOwnProperty("d") ? msg.d : msg;
        OnSucessCallBack(data);
    },
    error: function (xhr, status, error) {
        alert(xhr.statusText);
    }
});

function OnSuccessCallData(DataFromServer) {
 // your handler for success    
}

and then on the server side, in the code behind file that’s auto-generated in your AppCode folder, you write something like this:

using System.Web.Services;
using System.Web.Script.Serialization;

    [System.Web.Script.Services.ScriptService]
    public class YourWebServiceName : System.Web.Services.WebService
    {
        [WebMethod]
        public string yourmethodname(string TheData)
        {
          JavascriptSerializer YourSerializer = new JavascriptSerializer();
          // custom serializer if you need one 
          YourSerializer.RegisterConverters(new JavascriptConverter  [] { new YourCustomConverter() });

          //deserialization
          TheData.Deserialize(TheData);

          //serialization  
          TheData.Serialize(TheData);
        }
    }

If you don’t use a custom converter, the properties between the json string and the c# class definition of your server-side object must match for the deserialization to work. For the serialization, if you don’t have a custom converter, the json string will include every property of your c# class. You can add [ScriptIgnore] just before a property definition in your c# class and that property will be ignored by the serializer if you don’t specify a custom converter.