I recently encountered this problem and stumbled upon this question.

I resolved it with a much easier way.

Method One

You can either remove the dataType: 'json' property from the object literal…

Method Two

Or you can do what @Sagiv was saying by returning your data as Json.

The reason why this parsererror message occurs is that when you simply return a string or another value, it is not really Json, so the parser fails when parsing it.

So if you remove the dataType: json property, it will not try to parse it as Json.

With the other method if you make sure to return your data as Json, the parser will know how to handle it properly.

See the answer by @david-east for the correct way to handle the issue

This answer is only relevant to a bug with jQuery 1.5 when using the file: protocol.

I had a similar problem recently when upgrading to jQuery 1.5. Despite getting a correct response the error handler fired. I resolved it by using the complete event and then checking the status value. e.g:

complete: function (xhr, status) {
    if (status === 'error' || !xhr.responseText) {
        handleError();
    }
    else {
        var data = xhr.responseText;
        //...
    }
}

You have specified the ajax call response dataType as:

‘json’

where as the actual ajax response is not a valid JSON and as a result the JSON parser is throwing an error.

The best approach that I would recommend is to change the dataType to:

‘text’

and within the success callback validate whether a valid JSON is being returned or not, and if JSON validation fails, alert it on the screen so that its obvious for what purpose the ajax call is actually failing. Have a look at this:

$.ajax({
    url: '/Admin/Ajax/GetViewContentNames',
    type: 'POST',
    dataType: 'text',
    data: {viewID: $("#view").val()},
    success: function (data) {
        try {
            var output = JSON.parse(data);
            alert(output);
        } catch (e) {
            alert("Output is not valid JSON: " + data);
        }
    }, error: function (request, error) {
        alert("AJAX Call Error: " + error);
    }
});

the problem is that your controller returning string or other object that can’t be parsed.
the ajax call expected to get Json in return. try to return JsonResult in the controller like that:

 public JsonResult YourAction()
    {
        ...return Json(YourReturnObject);

    }

hope it helps 🙂

There are lots of suggestions to remove

dataType: "json"

While I grant that this works it’s ignoring the underlying issue. If you’re confident the return string really is JSON then look for errant whitespace at the start of the response. Consider having a look at it in fiddler. Mine looked like this:

Connection: Keep-Alive
Content-Type: application/json; charset=utf-8

{"type":"scan","data":{"image":"./output/ou...

In my case this was a problem with PHP spewing out unwanted characters (in this case UTF file BOMs). Once I removed these it fixed the problem while also keeping

dataType: json

Your JSON data might be wrong. http://jsonformatter.curiousconcept.com/ to validate it.

Make sure that you remove any debug code or anything else that might be outputting unintended information. Somewhat obvious, but easy to forgot in the moment.

I don’t know if this is still actual but problem was with Encoding. Changing to ANSI resolved the problem for me.

If you get this problem using HTTP GET in IE I solved this issue by setting the cache: false.
As I used the same url for both HTML and json requests it hit the cache instead of doing a json call.

$.ajax({
    url: '/Test/Something/',
    type: 'GET',
    dataType: 'json',
    cache: false,
    data: { viewID: $("#view").val() },
    success: function (data) {
        alert(data);
    },
    error: function (data) {
        debugger;
        alert("Error");
    }
});

you should remove the dataType: “json”. Then see the magic… the reason of doing such thing is that you are converting json object to simple string.. so json parser is not able to parse that string due to not being a json object.

this.LoadViewContentNames = function () {
$.ajax({
    url: '/Admin/Ajax/GetViewContentNames',
    type: 'POST',
    data: { viewID: $("#view").val() },
    success: function (data) {
        alert(data);
    },
    error: function (data) {
        debugger;
        alert("Error");
    }
 });
};

incase of Get operation from web .net mvc/api, make sure you are allow get

     return Json(data,JsonRequestBehavior.AllowGet);

If you don’t want to remove/change dataType: json, you can override jQuery’s strict parsing by defining a custom converter:

$.ajax({
    // We're expecting a JSON response...
    dataType: 'json',

    // ...but we need to override jQuery's strict JSON parsing
    converters: {
        'text json': function(result) {
            try {
                // First try to use native browser parsing
                if (typeof JSON === 'object' && typeof JSON.parse === 'function') {
                    return JSON.parse(result);
                } else {
                    // Fallback to jQuery's parser
                    return $.parseJSON(result);
                }
            } catch (e) {
               // Whatever you want as your alternative behavior, goes here.
               // In this example, we send a warning to the console and return 
               // an empty JS object.
               console.log("Warning: Could not parse expected JSON response.");
               return {};
            }
        }
    },

    ...

Using this, you can customize the behavior when the response cannot be parsed as JSON (even if you get an empty response body!)

With this custom converter, .done()/success will be triggered as long as the request was otherwise successful (1xx or 2xx response code).

I was also getting “Request return with error:parsererror.” in the javascript console.
In my case it wasn´t a matter of Json, but I had to pass to the view text area a valid encoding.

  String encodedString = getEncodedString(text, encoding);
  view.setTextAreaContent(encodedString);

I have encountered such error but after modifying my response before sending it to the client it worked fine.

//Server side
response = JSON.stringify('{"status": {"code": 200},"result": '+ JSON.stringify(result)+'}');
res.send(response);  // Sending to client

//Client side
success: function(res, status) {
    response = JSON.parse(res); // Getting as expected
    //Do something
}

I had the same problem, turned out my web.config was not the same with my teammates.
So please check your web.config.

Hope this helps someone.

I ran into the same issue. What I found to solve my issue was to make sure to use double quotes instead of single quotes.

echo "{'error':'Sorry, your file is too large. (Keep it under 2MB)'}";
-to-
echo '{"error":"Sorry, your file is too large. (Keep it under 2MB)"}';

When you are using dataType: 'json' your return type must be Json.
You can use contentType: "application/json; charset=utf-8" rather than dataType: 'json'

100% correct

For me what fixes the issue was using returning Task<JsonResult> after serializing it:

[HttpPost, Route("GetSomeText")]
public async Task<JsonResult> GetSomeText(SomeRequest request)
{
    string result = "some text";
    return Json(JsonConvert.SerializeObject(result));
}

The problem

window.JSON.parse raises an error in $.parseJSON function.

<pre>
$.parseJSON: function( data ) {
...
// Attempt to parse using the native JSON parser first
if ( window.JSON && window.JSON.parse ) {
return window.JSON.parse( data );
}
...
</pre>

My solution

Overloading JQuery using requirejs tool.

<pre>
define(['jquery', 'jquery.overload'], function() { 
    //Loading jquery.overload
});
</pre>

jquery.overload.js file content

<pre>
define(['jquery'],function ($) { 

    $.parseJSON: function( data ) {
        // Attempt to parse using the native JSON parser first
        /**  THIS RAISES Parsing ERROR
        if ( window.JSON && window.JSON.parse ) {
            return window.JSON.parse( data );
        }
        **/

        if ( data === null ) {
            return data;
        }

        if ( typeof data === "string" ) {

            // Make sure leading/trailing whitespace is removed (IE can't handle it)
            data = $.trim( data );

            if ( data ) {
                // Make sure the incoming data is actual JSON
                // Logic borrowed from http://json.org/json2.js
                if ( rvalidchars.test( data.replace( rvalidescape, "@" )
                    .replace( rvalidtokens, "]" )
                    .replace( rvalidbraces, "")) ) {

                    return ( new Function( "return " + data ) )();
                }
            }
        }

        $.error( "Invalid JSON: " + data );
    }

    return $;

});
</pre>