code: function(xhr, promise) {
              // for XDomainRequest, we need "onload" instead of "onreadystatechange"
              xhr.onreadystatechange = function() {
                  // CANNOT console xhr.responseText here! IE9 will throw an error:
                  // you can only acces it after (xhr.readyState===4)
                  // also check xhr._aborted --> IE9 comes here after aborted and will throw an error when reading xhr"s native properties
                  if (!xhr._aborted && (xhr.readyState===4)) {
                      clearTimeout(xhr._timer);
                      if ((xhr.status>=200) && (xhr.status<300)) {
                          // In case streamback function is set, but when no intermediate stream-data was send
                          // (or in case of XDR: below 2kb it doesn"t call onprogress)
                          // --> we might need to call onprogress ourselve.
                          if (xhr._isStream && !xhr._gotstreamed) {
                              xhr.onprogress(xhr.responseText);
                          }
                          if (xhr._fileProgress && !xhr._gotstreamed) {
                              xhr.onprogress({
                                  lengthComputable: true,
                                  loaded: 1,
                                  total: 1
                              });
                          }
                          promise.fulfill(xhr);
                      }
                      else {
                          promise.reject(xhr.statusText || (UNKNOW_ERROR));
                      }
                  }
              };
              xhr.onerror = function() {
                  clearTimeout(xhr._timer);
                  promise.reject(XHR_ERROR);
              };
          }
docs: Adds 2 methods on the xhr-instance which are used by xhr when events occur:
  
  xhr.onreadystatechange()
  xhr.ontimeout()  // only XMLHttpRequest2
  
  These events are responsible for making the Promise resolve.
  @method _setReadyHandle
  @param xhr {Object} containing the xhr-instance
  @param fulfill {Function} reference to the Promise fulfill-function
  @param reject {Function} reference to the Promise reject-function
  @private