When exactly does jquery.ajax run the fail callback?

Question

I cannot find this in the documentation. I also did a run through the jquery source and can't find any more info.

By using jquery.ajax, when can I expect the fail callback to be run?

Apart of the following:

• connection problem ( e.g. mobile device lost connection )

• server is down and does not respond

  // EDIT: added after comments, a lot of thanks to @charlietfl :

• http error code equal to or greater then 400

• missing CORS headers

what are the other cases when jquery will run the fail callback?

Answer 1

When the response status returned is 4xx or 5xx, which indicates a client-side or server-side error respectively. Here's the entire list of such status codes.