[jquery] jQuery: How to get the HTTP status code from within the $.ajax.error method?

I'm using jQuery to make an AJAX request. I want to perform different actions whether or not the HTTP status code is a 400 error or a 500 error. How can I achieve this?

$.ajax({
    type: 'POST',
    url: '/controller/action',
    data: $form.serialize(),
    success: function(data){
        alert('horray! 200 status code!');
    },
    error: function(data){
        //get the status code
        if (code == 400) {
            alert('400 status code! user error');
        }
        if (code == 500) {
            alert('500 status code! server error');
        }
    },
});

Update:

@GeorgeCummins mentioned that it "seemed odd" to work with the response body. This is the first time that I've attempted doing this sort of thing. Is my approach not a best-practice? What would you recommend? I created another StackOverflow question for this here: What response/status code should I send to an AJAX request when there is a user/form validation error?

use

   statusCode: {
    404: function() {
      alert('page not found');
    }
  }

-

$.ajax({
    type: 'POST',
    url: '/controller/action',
    data: $form.serialize(),
    success: function(data){
        alert('horray! 200 status code!');
    },
    statusCode: {
    404: function() {
      alert('page not found');
    },

    400: function() {
       alert('bad request');
   }
  }

});

An other solution is to use the response.status function. This will give you the http status wich is returned by the ajax call.

function checkHttpStatus(url) {     
    $.ajax({
        type: "GET",
        data: {},
        url: url,
        error: function(response) {
            alert(url + " returns a " + response.status);
        }, success() {
            alert(url + " Good link");
        }
    });
}

You should create a map of actions using the statusCode setting:

$.ajax({
  statusCode: {
    400: function() {
      alert('400 status code! user error');
    },
    500: function() {
      alert('500 status code! server error');
    }
  }
});

Reference (Scroll to: 'statusCode')

EDIT (In response to comments)

If you need to take action based on the data returned in the response body (which seems odd to me), you will need to use error: instead of statusCode:

error:function (xhr, ajaxOptions, thrownError){
    switch (xhr.status) {
        case 404:
             // Take action, referencing xhr.responseText as needed.
    }
}