jquery ajax call return JSON parsing error

Question

I am using jquery to call an ajax wcf method that returns a list of objects as a JSON string. The JSON string looks like this when inspecting it in fiddler2 (in TextView):

{"d":"[{\"ID\":\"6b2b8c62-31ce-4df2-982b-054ff5f6be72\",\"Name\":\"Carol\",\"Surname\":\"IrishWife\"},{\"ID\":\"d254740a-0a0f-4a1e-9e4f-0812227dd5af\",\"Name\":\"Willie\",\"Surname\":\"Le Roux\"},{\"ID\":\"660bf0dd-436a-4588-a9c0-19fd6fdcee23\",\"Name\":\"Emmas\",\"Surname\":\"Mum\"},{\"ID\":\"6b9403c5-b728-4e96-bcb1-203e7472eec3\",\"Name\":\"Owen\",\"Surname\":\"Lima\"},{\"ID\":\"d52c08fb-4418-4600-960f-243ff4443ee6\",\"Name\":\"Tim\",\"Surname\":\"Lee\"},{\"ID\":\"e2aacf5b-8855-44ce-9338-3d39f8ab3349\",\"Name\":\"Marcello\",\"Surname\":\"MT\"},{\"ID\":\"578be087-8385-46d6-89de-3db31d352cbc\",\"Name\":\"Carlyn\",\"Surname\":\"Homegroup\"},{\"ID\":\"4c805825-2bee-447a-8b75-41ead17db33e\",\"Name\":\"George\",\"Surname\":\"Homegroup\"},{\"ID\":\"ae48804f-5e78-42c8-9ba0-4214c98a5a89\",\"Name\":\"Isla\",\"Surname\":\"Le Roux\"},{\"ID\":\"f8be2f4f-fedb-4863-8a84-44fddea84ea9\",\"Name\":\"Peter\",\"Surname\":\"Anderson\"},{\"ID\":\"15e7644d-ec43-44ff-a959-47e00112da6b\",\"Name\":\"Kitty\",\"Surname\":\"Corbett\"},{\"ID\":\"8fd7fccc-335c-4d5c-93b5-4b00f96a9950\",\"Name\":\"Natalie\",\"Surname\":\"Archibald\"},{\"ID\":\"09b5aad2-2cf1-488a-962b-4d692b05ddea\",\"Name\":\"Miku\",\"Surname\":\"Heally\"},{\"ID\":\"affa369e-5af3-4537-a0f4-71422956da41\",\"Name\":\"Steven\",\"Surname\":\"Corbett\"},{\"ID\":\"65f57da3-4f88-4798-9590-83b4ccecfc44\",\"Name\":\"Tim\",\"Surname\":\"Archibald\"},{\"ID\":\"53bfb451-f66f-4b6e-b430-8d13c95b30d8\",\"Name\":\"Philip\",\"Surname\":\"MT\"},{\"ID\":\"c7f22b9b-4030-4f82-9f75-bbb726cabb73\",\"Name\":\"Vincent\",\"Surname\":\"Van Der Walt\"},{\"ID\":\"232577be-3165-4316-a20d-c2f2a09c5382\",\"Name\":\"Scott\",\"Surname\":\"Lynn\"},{\"ID\":\"913508a1-5dca-4504-8caf-c8e3dc386fc0\",\"Name\":\"Dan\",\"Surname\":\"MT\"},{\"ID\":\"36054a07-b14d-4c1c-b35f-e00875dde7e5\",\"Name\":\"Sarah\",\"Surname\":\"MT\"},{\"ID\":\"f14e7d98-e040-4ba9-928f-f2ff48116b0b\",\"Name\":\"Josh\",\"Surname\":\"IrishDude\"}]"}

When I inspect the result in fiddler's JSON View, it shows the following JSON:

d=[{"ID":"6b2b8c62-31ce-4df2-982b-054ff5f6be72","Name":"Carol","Surname":"IrishWife"},{"ID":"d254740a-0a0f-4a1e-9e4f-0812227dd5af","Name":"Willie","Surname":"Le Roux"},{"ID":"660bf0dd-436a-4588-a9c0-19fd6fdcee23","Name":"Emmas","Surname":"Mum"},{"ID":"6b9403c5-b728-4e96-bcb1-203e7472eec3","Name":"Owen","Surname":"Lima"},{"ID":"d52c08fb-4418-4600-960f-243ff4443ee6","Name":"Tim","Surname":"Lee"},{"ID":"e2aacf5b-8855-44ce-9338-3d39f8ab3349","Name":"Marcello","Surname":"MT"},{"ID":"578be087-8385-46d6-89de-3db31d352cbc","Name":"Carlyn","Surname":"Homegroup"},{"ID":"4c805825-2bee-447a-8b75-41ead17db33e","Name":"George","Surname":"Homegroup"},{"ID":"ae48804f-5e78-42c8-9ba0-4214c98a5a89","Name":"Isla","Surname":"Le Roux"},{"ID":"f8be2f4f-fedb-4863-8a84-44fddea84ea9","Name":"Peter","Surname":"Anderson"},{"ID":"15e7644d-ec43-44ff-a959-47e00112da6b","Name":"Kitty","Surname":"Corbett"},{"ID":"8fd7fccc-335c-4d5c-93b5-4b00f96a9950","Name":"Natalie","Surname":"Archibald"},{"ID":"09b5aad2-2cf1-488a-962b-4d692b05ddea","Name":"Miku","Surname":"Heally"},{"ID":"affa369e-5af3-4537-a0f4-71422956da41","Name":"Steven","Surname":"Corbett"},{"ID":"65f57da3-4f88-4798-9590-83b4ccecfc44","Name":"Tim","Surname":"Archibald"},{"ID":"53bfb451-f66f-4b6e-b430-8d13c95b30d8","Name":"Philip","Surname":"MT"},{"ID":"c7f22b9b-4030-4f82-9f75-bbb726cabb73","Name":"Vincent","Surname":"Van Der Walt"},{"ID":"232577be-3165-4316-a20d-c2f2a09c5382","Name":"Scott","Surname":"Lynn"},{"ID":"913508a1-5dca-4504-8caf-c8e3dc386fc0","Name":"Dan","Surname":"MT"},{"ID":"36054a07-b14d-4c1c-b35f-e00875dde7e5","Name":"Sarah","Surname":"MT"},{"ID":"f14e7d98-e040-4ba9-928f-f2ff48116b0b","Name":"Josh","Surname":"IrishDude"}]

So fiddler can parse it successfully, but on the client, the jquery ajax error callback function displays the following error:

Error: No conversion from text to application/json

The wcf method is defined as follows:

    [OperationContract]
    [WebGet(ResponseFormat=WebMessageFormat.Json)]
    public string GetPeople(Guid groupId)
    {
        using (SchedulerContext context = new SchedulerContext())
        {
            JavaScriptSerializer ser = new JavaScriptSerializer();

            var query = from p in context.People
                        where p.Group_ID == groupId
                        select new
                        {
                            p.ID,
                            p.Name,
                            p.Surname
                        };

            return ser.Serialize(query.ToArray());
        }   
    }

And finally, the calling jquery is:

$.ajax(
        {
            type: "GET",
            dataType: "application/json",
            contentType: "json",
            data: { groupId: 'ae09a080-5d7c-4e92-9a87-591574b7c4b8' },
            url: "WebAPI.svc/GetPeople",
            error: function (jqXHR, textStatus, errorThrown) {
                alert("error");
            },
            success: function (msg) {
                alert(msg.d[0].Name);
            }
        }
);

Thanks in advance!

UPDATE: Thanks to @user1370958, one step closer to the solution.

When changing the error callback function to the following it successfully returns the result...

error: function (jqXHR, textStatus, errorThrown) {
    var test = $.parseJSON(jqXHR.responseText);
    var test2 = $.parseJSON(test.d);
    alert(test2[0].Name);
},

Not sure why, but I have to parse the result and then parse the nested objects inside that. I'm assuming if any of my returned types contained complex objects it would also have needed another parse...

Answer 1

Here, "application/json" is not a valid value for the dataType property. I changed it to "json" in my project and the same problem was solved.

Please check details here (comment #7): http://bugs.jquery.com/ticket/8216

Answer 2

Try adding the MIME type in your server-side code:

Response.ContentType = "application/json";

Answer 3

With WCF 4.0, you can add an attribute called automaticFormatSelectionEnabled which allows the service to look at the Accept header in the HTTP request to determine what format to return. As long as what you are returning is serializable, WCF will handle the correct serialization for you. In your jQuery ajax call, the Accept header is added by including accepts: {json: "application/json"}.