title: How to get response code in backbone js?
body: <p>How can I get Response code in backbone js when i fetch the result using fetch() method of collection?
  I know it executes error callback function when the response code is like 4xx and success callback method when the Response code is like 2xx.</p>
  
  <pre><code>var x = user.fetch({
      error:   function(model, xhr, options){
         alert('Error on fetch')
         console.log(xhr.responseText);
      },
      success: function(model, response, options) {
          alert(user.toJSON());
      }
  </code></pre>
  
  <p>Here I want to get Response code, No matter whether It is an error callback or success callback.</p>
  
  <p>Thanks in Advance.</p>