JSON parsing failed due to the occurrence of an unexpected token "<" at the beginning of the file

I seem to be encountering an issue with retrieving data using ajax. When I test locally, it returns the desired output. However, upon publishing the project on the server with IIS, it shows a HTML Code of my page along with an error message "syntax Error: Unxpected token < in JSON as position 0". Any assistance would be greatly appreciated. Thank you :)

Below is the code snippet:

Controller: 
[HttpGet]
    public ActionResult getregion(string zname)
    {
        SelectList list = RegionList(zname);

        var serializedData = JsonConvert.SerializeObject(list, Formatting.Indented,
          new JsonSerializerSettings
          {
              ContractResolver = new CamelCasePropertyNamesContractResolver(),
              NullValueHandling = NullValueHandling.Ignore
          });

        return Json(list, JsonRequestBehavior.AllowGet);
    }

The above code is designed to fetch a list of regions in JSON format.

public SelectList RegionList(string zname)
    {
        CustomerModel cust = new CustomerModel();
        List<SelectListItem> regionname = new List<SelectListItem>();
        try
        {

            dt1.Clear();
            MySqlConnection mycon = new MySqlConnection(conn.getconnections("mysql"));
            mycon.Open();
            if (zname == null || zname == "")
            {
                cmdsql = mycon.CreateCommand(); cmdsql.CommandText = "SELECT regionname FROM tbl_region WHERE STATUS=1 group by regionname order by regionname asc";
            }
            else
            {
                cmdsql = mycon.CreateCommand(); cmdsql.CommandText = string.Format("SELECT regionname FROM tbl_region WHERE STATUS=1 and zonecode='{0}'  group by regionname   order by regionname asc", getzonecode(zname));
            }
            drsql = cmdsql.ExecuteReader();
            try
            {
                if (drsql.HasRows)
                {
                    regionname.Add(new SelectListItem { Text = "- Select -", Value = "", Selected = true });
                    regionname.Add(new SelectListItem { Text = "All Region", Value = "AllRegion" });
                    while (drsql.Read())
                    {
                        regionname.Add(new SelectListItem { Text = drsql["regionname"].ToString().ToUpper().Trim(), Value = drsql["regionname"].ToString().ToUpper().Trim() });
                    }
                }
            }
            catch (Exception ex) { cust.WriteToFile(ex.ToString()); return null; }
        }
        catch (Exception ex) { cust.WriteToFile(ex.ToString()); }
        return new SelectList(regionname, "Value", "Text");
    }

This method is utilized for fetching the list of regions.

 JAVASCRIPT:
 $(function () {
    $('#zoneitem').change(function () {
        var item = $('#zoneitem').val();
        var region = $("#regionitem");
        region.empty();

        if (item != "") {
            $("#reportsitem").val($("#reportsitem option:first").val());
        }
        $.ajax({
            type: "GET",
            url: "Home/getregion",
            contentType: "application/json; charset=utf-8",
            data: { zname: item },
            cache: false,
            dataType: "json",
            success: function (result) {
                for (var i = 0; i < result.length; i++) {
                    region.append('<option value="' + result[i].Value.trim() + '">' + result[i].Text.trim() + '</option>');
                }
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
                alert(errorThrown);                    
            }
        });
    });
});

This pertains to my _reference.js code, where debugging indicates that the returned result is in HTML format of my webpage. Kindly assist me in resolving this issue. Despite researching and attempting various solutions, the problem persists.

Answer №1

When analyzing why your response is appearing in HTML format, there are multiple potential reasons to consider:

  1. If the URL for your ajax request does not exist, you may encounter a 404 Not Found Error
  2. If the user ID being used lacks authorization to access the server resource, a 401 Unauthorized Error could occur
  3. A firewall blocking the ajax request might result in a 403 Forbidden Error
  4. If issues in the server-side code cause it to malfunction, a 500 Internal Server Error may be seen

While other scenarios are possible, focusing on point number 4, if you see responses similar to the following:

<html>
    <head>
        <title>500 Internal Server Error</title>
    </head>
    <body>
        <h1>Internal Server Error</h1>
        <p>The server encountered an internal error or misconfiguration and     
        was unable to complete your request.</p>
        <p>Please contact the server administrator, <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="116674737c7062657463517469707c617d743f727e7c">[email protected]</a> 
        and inform them of the time the error occurred, as well as any actions that may have triggered it.</p>
        <hr>
        <address>Apache Server at xyz.com Port 80</address>
    </body>
</html>

You may encounter an issue with JSON parsing, resulting in a syntax error due to encountering "<" from "<html>" in the response.

To resolve this, per @torazaburo's suggestion, closely examine the response in your network tab and adjust your server-side code based on the provided messages.

Answer №2

I've managed to identify the issue with my code - it seems to be related to my js file. The problem lies in the URL line on the server side, where it is unable to locate the folder name of my application and redirects to the Controller.

Instead of accessing ip address/my folder application, it now routes to ip address/Home/getregion, which leads to the controller.

To resolve this, I made the following changes:

$.ajax({
        type: "GET",
        url: " my folder application /Home/getregion",
        contentType: "application/json; charset=utf-8",
        data: { zname: item },
        cache: false,
        dataType: "json",
        success: function (result) {
            for (var i = 0; i < result.length; i++) {
                region.append('<option value="' + result[i].Value.trim() + '">' + result[i].Text.trim() + '</option>');
            }
        },
        error: function (XMLHttpRequest, textStatus, errorThrown) {
            alert(errorThrown);                    
        }
    });

Could someone assist me in understanding why my application folder cannot be located? Thank you so much :)

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