How to force datatype as JSON in ASP.Net 2.0

I got the following working after spinning my head around a thousand times and then referring parserrror SyntaxError: Unexpected token < - Load Partial View using jQuery Ajax in ASP.NET MVC 4

I have the following code in my ASP.Net 2.0 project. It works – but to get it to work, I am using dataType: "html" . When I use JSON as datatype I get a parse error: Unexpected token <

How can we make it work with JSON ?

Note: Though I am using IE8, some of my users are still using IE6. So I need a solution that works in IE6 .

jQuery Ajax

   $.ajax({
            type: "GET",
            url: "admPlantParametersViewEdit.aspx/GetResult",
            contentType: "application/json; charset=utf-8",
            dataType: "html",
            success: function(msg) 
            {
                alert("Hi");
            },
            error: errorFunction
        });

VB.Net

   <WebMethod()> _
    Public Shared Function GetResult() As String

        Return "hello"

    End Function

Request and Response Headers

References

in request you need to set Accept: application/json ,the if you server has json support then it will send response in json automatically,

        type: "GET",
        url: "admPlantParametersViewEdit.aspx/GetResult",
        contentType: "application/json; charset=utf-8",
        Accept: application/json,

then in response header you should see

        content-type:application/json 

not content-type:text/html

I figured it out after referring following two posts

encosia - ASP.NET web services mistake: manual JSON serialization

encosia - ASMX ScriptService mistake: Installation and configuration

Since you're using .NET 2.0, the most likely culprit is that you've got the AJAX Extensions installed, but haven't updated your web.config to use that new handler for ASMX requests.

STEPS TO SOLVE:

   <httpHandlers>

    <remove verb="*" path="*.asmx"/>

    <add verb="*" path="*.asmx" validate="false" 
         type="System.Web.Script.Services.ScriptHandlerFactory,
         System.Web.Extensions, Version=1.0.61025.0,
                     Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

</httpHandlers>

As

  <httpModules>
    <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  </httpModules>

and

      <assemblies>
            <add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add assembly="System.Web.Extensions.Design, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>           
        </assemblies>

.4. Made it as POST and json

  $.ajax({
            type: "POST",
            url: "admPlantParametersViewEdit.aspx/GetResult",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function(msg) 
            {
                alert(msg.d);
                alert(msg);
            },
            error: errorFunction
        });

This answer won't be complete without quoting the following lines from encosia

The ability for ASMX services to return raw JSON is made possible by two key features originally added by the ASP.NET AJAX Extensions v1.0

Good Reads

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