title: How to get the error response in Backbone's model.save error callback?
body: <p>Backbone's error callback on <code>model.save</code> only takes two arguments <code>error: function(model, response){}</code>. In my application, if optimistic locking fails a <code>409 conflict</code> status is set (which is easily retrievable). However, the server also sends a custom error message detailing the problem. </p>
  
  <p>Now the server sends an updated JSON response with the <em>updated model</em> <strong><em>along with an error message</em></strong> stating what the problem was. It seems, backbone suppresses this error. As per jquery's error callback the signature is <code>error(jqXHR, textStatus, errorThrown)</code>. Seems Backbone discards the last part and thus I can't seem to get my hands on the server's custom response.</p>
  
  <p>Is this a good practice? I really don't wish to duplicate backbone's functionality of save just to have access to the <code>errorThrown</code> parameter. Is there a seamless way to access the <code>errorThrown</code>? Or is it a better practice to NOT have the server send a custom response, only the code and have the client build the response for viewing??</p>