code: function(xhr) {
      var response = {
          headers: {},
          statusCode: xhr.status
      };
  
      var headerPairs = xhr.getAllResponseHeaders().split('\u000d\u000a');
      for (var i = 0; i < headerPairs.length; i++) {
          var headerPair = headerPairs[i],
              index = headerPair.indexOf('\u003a\u0020');
  
          if (index > 0) {
              var key = headerPair.substring(0, index);
              var val = headerPair.substring(index + 2);
              response.headers[key.toLowerCase()] = val;
          }
      }
  
      return response;
  }
docs: Normalize a response into a common format for both environments
  
  @param  {XMLHttpRequest} xhr
  @return {Object}