JQuery ajax call executes error on 200 [duplicate]

Answer 1

From MSDN, HttpStatusCode.OK is defined as follows (emphasis mine):

Equivalent to HTTP status 200. OK indicates that the request succeeded and that the requested information is in the response. This is the most common status code to receive.

Because a 200 implies some content is sent with the response (even an empty JSON object literal would be fine), you can run into problems if jQuery's Ajax implementation assumes a non-zero length response but does not receive it, especially if it tries parsing JSON (and possibly XML) from it. This is why John S makes the suggestion of changing the dataType to text; doing so would allow you to take specific action when receving an empty response.

On the other hand, HttpStatusCode.NoContent is defined as (emphasis mine):

Equivalent to HTTP status 204. NoContent indicates that the request has been successfully processed and that the response is intentionally blank.

In your particular situation, it may make more sense to set the status code to HttpStatusCode.NoContent to ensure that jQuery Ajax understands that it does not need to attempt any parsing/processing of the response.

Answer 2

This is how jQuery works.

JQuery will assume the response is JSON if either:

1. You specify dataType: 'json' in the ajax call, or
2. You do not include the dataType setting but jQuery detects the response is JSON because of a response header.

And when jQuery assumes the response is JSON, it automatically tries to parse the response into objects before it calls the success handler. If the parse fails, the error handler is called instead.

From the jQuery documentation:

As of jQuery 1.9, an empty response is also rejected; the server should return a response of null or {} instead.

I don't know why jQuery couldn't make an exception for an empty response and treat it the same as null, or even as undefined, but if you cannot (or won't) change the response, a work-around would be to specify dataType: 'text' and then parse the response yourself.

$.ajax(url, {
    type: 'post',
    dataType: 'text',
    data: params,
    success: function(text) {
        if (text) {
            var data = jQuery.parseJSON(text);
            // ...
        }
    }
});