Ajax request returns 200 OK, but an error event is fired instead of success

jQuery.ajax attempts to convert the response body depending on the specified dataType parameter or the Content-Type header sent by the server. If the conversion fails (e.g. if the JSON/XML is invalid), the error callback is fired.

Your AJAX code contains:

dataType: "json"

In this case jQuery:

Evaluates the response as JSON and returns a JavaScript object. […] The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. […] an empty response is also rejected; the server should return a response of null or {} instead.

Your server-side code returns HTML snippet with 200 OK status. jQuery was expecting valid JSON and therefore fires the error callback complaining about parseerror.

The solution is to remove the dataType parameter from your jQuery code and make the server-side code return:

Content-Type: application/javascript

alert("Record Deleted");

But I would rather suggest returning a JSON response and display the message inside the success callback:

Content-Type: application/json

{"message": "Record deleted"}

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You simply have to remove the dataType: "json" in your AJAX call

$.ajax({
    type: 'POST',
    url: 'Jqueryoperation.aspx?Operation=DeleteRow',
    contentType: 'application/json; charset=utf-8',
    data: json,
    dataType: 'json', //**** REMOVE THIS LINE ****//
    cache: false,
    success: AjaxSucceeded,
    error: AjaxFailed
});

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I've had some good luck with using multiple, space-separated dataTypes (jQuery 1.5+). As in:

$.ajax({
    type: 'POST',
    url: 'Jqueryoperation.aspx?Operation=DeleteRow',
    contentType: 'application/json; charset=utf-8',
    data: json,
    dataType: 'text json',
    cache: false,
    success: AjaxSucceeded,
    error: AjaxFailed
});

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This is just for the record since I bumped into this post when looking for a solution to my problem which was similar to the OP's.

In my case my jQuery Ajax request was prevented from succeeding due to same-origin policy in Chrome. All was resolved when I modified my server (Node.js) to do:

response.writeHead(200,
          {
            "Content-Type": "application/json",
            "Access-Control-Allow-Origin": "http://localhost:8080"
        });

It literally cost me an hour of banging my head against the wall. I am feeling stupid...

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I reckon your aspx page doesn't return a JSON object. Your page should do something like this (page_load)

var jSon = new JavaScriptSerializer();
var OutPut = jSon.Serialize(<your object>);

Response.Write(OutPut);

Also, try to change your AjaxFailed:

function AjaxFailed (XMLHttpRequest, textStatus) {

}

textStatus should give you the type of error you're getting.

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I have faced this issue with an updated jQuery library. If the service method is not returning anything it means that the return type is void.

Then in your Ajax call please mention dataType='text'.

It will resolve the problem.

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You just have to remove dataType: 'json' from your header if your implemented Web service method is void.

In this case, the Ajax call don't expect to have a JSON return datatype.

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See this. It's also a similar problem. Working I tried.

Dont remove dataType: 'JSON',

Note: Your response data should be in json format

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Use the following code to ensure the response is in JSON format (PHP version)...

header('Content-Type: application/json');
echo json_encode($return_vars);
exit;

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I had the same issue. My problem was my controller was returning a status code instead of JSON. Make sure that your controller returns something like:

public JsonResult ActionName(){
   // Your code
   return Json(new { });
}

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Another thing that messed things up for me was using localhost instead of 127.0.0.1 or vice versa. Apparently, JavaScript can't handle requests from one to the other.

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If you always return JSON from the server (no empty responses), dataType: 'json' should work and contentType is not needed. However make sure the JSON output...

is valid (JSONLint)

is serialized (JSONMinify)

jQuery AJAX will throw a 'parseerror' on valid but unserialized JSON!

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I had the same problem. It was because my JSON response contains some special characters and the server file was not encoded with UTF-8, so the Ajax call considered that this was not a valid JSON response.

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Your script demands a return in JSON data type.

Try this:

private string test() {
  JavaScriptSerializer js = new JavaScriptSerializer();
 return js.Serialize("hello world");
}

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