Rule Definition
Ensure that each web service callback is going to be properly checked in order to make sure you will not miss any problem that occurred in your application and you will give the information to the user.

Remediation
Always implement success, error, complete callbacks before jQuery 3.0 Always implement done, fail, always callbacks with jQuery 3.0 (and latest)

Violation Code Sample

// error callback is missing
$.ajax({
   type: 'POST',
   url: '_auth/login',
   success: function(res, status, xhr) { window.location.reload(); },
   complete: function(xhr, status, err) {
   }
});

-------------------------------------------
// fail callback is missing
$.ajax({
   type: 'POST',
   url: '_auth/login'
})
.done(successHandler)
.always();

Fixed Code Sample

$.ajax({
   type: 'POST',
   url: '_auth/login',
   success: function(res, status, xhr) { window.location.reload(); },
   error: function(res, status, xhr) { window.location.reload(); },
   complete: function(xhr, status, err) {
   }
});

-------------------------------------------
$.ajax({
   type: 'POST',
   url: '_auth/login'
})
.done(successHandler)
.fail(errorHandler)
.always();

https://api.jquery.com/jquery.ajax/