title: Backbonejs collection fetch error detect XHR object
body: <p>In my backbone collection, I have</p>
  
  <pre><code>fetch_data: function(data, callback) {
    this.fetch({
      data: data,
      success: callback,
      error: function() {
        // detect of HTTP code here
      }
    });
  }
  </code></pre>
  
  <p>And I want to check the HTTP header status code within error. How can I access XHR object within the error function?</p>