jquery 3 ajax().fail(jqXHR) status is always 0

Question

When maintaining my (old) web app I found out that error handling stopped working, probably already some time ago. Here is my old code which was working:

$.ajax({
  url: this.url,
  type: 'post',
  data: jsonsendobject,
  dataType: 'json',
  crossDomain: true, // comment this out when not in test mode from foreign webapp
  xhrFields: { withCredentials: true }, // comment this out when not in thest mode from foreign webapp

  }).done(function(data, textStatus, jqXHR) {

    // do something after it worked

  }).fail(function(jqXHR,textStatus,errorThrown) {

    console.log(JSON.stringify(jqXHR));
    // now always returns: {"readyState":0,"status":0,"statusText":"error"}             

  });

Now jqXHR always returns 0, even if the server obviously sends a 500 status code.

I searched a lof of questions here at stackoverflow but most of them were asked around 2011 and the quality of answers unfortunately is bad. Here are different opinions I read:

jquery as of 2.0 (of 3.0) does not support the jqXHR object anymore. It is returned for compatibility reasons but status is always 0.
jqXHR object is empty when used with HTTP 2.0
HTTP status codes don't work if dataType is "json" (or "jsonp")
HTTP status codes do not work if it is crossDomain (or a local web app)

But if I read the documentation (https://api.jquery.com/jquery.ajax) I cannot find evidence that one of these answers is correct,

I understand that I could probably do something like this

$.ajax({
  statusCode: {
    404: function() {
      alert( "page not found" );
    }
  }
});

But I'd rather like to get the status code and decide after (together with other parameters) what to do about it.

What is the working, non-deprecated way of getting the status code within the .fail() call?

jquery 3 ajax().fail(jqXHR) status is always 0

0 Answers