How to use the leancloud-realtime.Event.OFFLINE function in leancloud-realtime

}
    $scope.$digest();
  };

  const client = $scope.imClient;
  client.on(Event.MESSAGE, messageHandler);
  client.on(Event.INVITED, invitedHandler);
  client.on(Event.UNREAD_MESSAGES_COUNT_UPDATE, () => {
    $scope.$emit('unreadCountUpdate', getTotalUnreadCount());
  });
  client.on(Event.DISCONNECT, () => {
    $scope.networkError = '连接已断开';
    $scope.networkErrorIcon = 'sync_problem';
    $scope.$digest();
  });
  client.on(Event.OFFLINE, () => {
    $scope.networkError = '网络不可用，请检查网络设置';
    $scope.networkErrorIcon = 'signal_wifi_off';
    $scope.networkShowRetry = false;
    $scope.$digest();
  });
  client.on(Event.ONLINE, () => {
    $scope.networkError = '网络已恢复';
    $scope.$digest();
  });
  client.on(Event.SCHEDULE, (attempt, time) => {
    $scope.networkError = `${time / 1000}s 后进行第 ${attempt + 1} 次重连`;
    $scope.networkShowRetry = true;
    $scope.$digest();
  });
  client.on(Event.RETRY, attempt => {
    $scope.networkError = `正在进行第 ${attempt + 1} 次重连`;

$scope.$on("$destroy", () => {
    client.off(Event.MESSAGE, messageHandler);
    client.off(Event.INVITED, invitedHandler);
    [
      Event.UNREAD_MESSAGES_COUNT_UPDATE,
      Event.DISCONNECT,
      Event.OFFLINE,
      Event.ONLINE,
      Event.SCHEDULE,
      Event.RETRY,
      Event.RECONNECT,
      Event.RECONNECT_ERROR
    ].forEach(event => client.off(event));
  });