jquery ajax 200 OK JSON.ParseError

Question

I have a control which has a textbox which, when its content changes, will tricker this javascript function:

page parameter is document.URL as the control has no attached .asxc page and fieldValue is value of the textbox.

function UpdateFieldsOnListSelection(page, fieldValue) {
    $.ajax({
        type: "POST",
        url: page + "/IsSelectedListPictureLibrary",
        data: { "libraryInfo": fieldValue },
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (data) {
            alert("Success!");
        },
        error: function (jqXHR, textStatus, errorThrown) {
            alert("jqXHR: " + jqXHR.status + "\ntextStatus: " + textStatus + "\nerrorThrown: " + errorThrown);
        }
    });
};

It keeps throwing this error:

jqXHR: 200
textStatus: parsererror
errorThrown: SyntaxError: JSON.parse: unexpected character

The code for IsSelectedListPictureLibrary:

[WebMethod]
public static bool IsSelectedListPictureLibrary(string libraryInfo)
{
    if (string.IsNullOrEmpty(libraryInfo)) return false;
    var common = new Utility();
    var storedLibraryInfo = common.GetStoredLibraryInfo(libraryInfo);
    if (storedLibraryInfo == null) return false;
    var web = SPContext.Current.Site.OpenWeb(storedLibraryInfo.WebId);
    var spList = web.Lists[storedLibraryInfo.LibraryId];
    if (spList.BaseTemplate == SPListTemplateType.PictureLibrary)
    {
        web.Dispose();
        return true;
    }
    web.Dispose();
    return false;
}

I have tried changing json in the ajax to jsonp, but same error occured.
I tried changing the format of data.

Any ideas?

Solution 1

Try to remove contentType and dataType from Ajax parameters and let them be identified automatically

Solution 2

Had the same problem with AJAX's 'post' command.

Sent a JSON post request, got a 200 OK repsponse but textStatus was parseerror and errorThrown was SyntaxError: JSON.parse: unexpected character.

This is my JS code:

$.post(url, JSON.stringify(reportVarsJson), function(response) {}, 'json')
.fail(function(jqXHR, textStatus, errorThrown) {
    alert('Error saving report request variables:\n\n' + jqXHR.responseText);
});

The problem turned out to be that my server view (Django) returned an empty response which was not a JSON response.

I changed my server view to return an empty json response and everything works well!