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

$scope.$digest();
  };
  const invitedHandler = (payload, conversation) => {
    if (conversation.transient) {
      // 暂态对话
      if ($scope.transConvs.indexOf(conversation) === -1) {
        $scope.transConvs.push(conversation);
      }
    } else if ($scope.normalConvs.indexOf(conversation) === -1) {
      $scope.normalConvs.push(conversation);
    }
    $scope.$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, () => {

$scope.$on("$destroy", () => {
      conversation.off(Event.MEMBERS_JOINED, membersJoinedHandler);
      conversation.off(Event.MEMBERS_LEFT, membersLeftHandler);
      conversation.off(Event.KICKED, kickedHandler);
      conversation.off(Event.INFO_UPDATED, infoUpdatedHandler);
      conversation.off(Event.MEMBER_INFO_UPDATED, memberInfoUpdateHandler);
      conversation.off(Event.MESSAGE, readMarker);
      conversation.off(Event.MESSAGE, messageUpdater);
      conversation.off(Event.LAST_DELIVERED_AT_UPDATE, receiptUpdateHandler);
      conversation.off(Event.LAST_READ_AT_UPDATE, receiptUpdateHandler);
      conversation.off('lastreadtimestampsupdate', receiptUpdateHandler);
      conversation.off(Event.MESSAGE_RECALL, replaceRecalledMessage);
      $scope.typingIndicator.off('change');
      document.removeEventListener("visibilitychange", handleVisibilityChange);
    });

$scope.$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));
  });

const receiptUpdateHandler = () => {
      $scope.$digest();
    };

    const handleVisibilityChange = () => {
      if (!document.hidden && conversation.unreadMessagesCount) {
        conversation.read();
      }
    };

    conversation.on(Event.MEMBERS_JOINED, membersJoinedHandler);
    conversation.on(Event.MEMBERS_LEFT, membersLeftHandler);
    conversation.on(Event.KICKED, kickedHandler);
    conversation.on(Event.INFO_UPDATED, infoUpdatedHandler);
    conversation.on(Event.MEMBER_INFO_UPDATED, memberInfoUpdateHandler);
    conversation.on(Event.MESSAGE, readMarker);
    conversation.on(Event.MESSAGE, messageUpdater);
    conversation.on(Event.LAST_DELIVERED_AT_UPDATE, receiptUpdateHandler);
    conversation.on(Event.LAST_READ_AT_UPDATE, receiptUpdateHandler);
    conversation.on('lastreadtimestampsupdate', receiptUpdateHandler);
    conversation.on(Event.MESSAGE_RECALL, replaceRecalledMessage);
    document.addEventListener("visibilitychange", handleVisibilityChange);

    $scope.$on("$destroy", () => {
      conversation.off(Event.MEMBERS_JOINED, membersJoinedHandler);
      conversation.off(Event.MEMBERS_LEFT, membersLeftHandler);
      conversation.off(Event.KICKED, kickedHandler);
      conversation.off(Event.INFO_UPDATED, infoUpdatedHandler);
      conversation.off(Event.MEMBER_INFO_UPDATED, memberInfoUpdateHandler);
      conversation.off(Event.MESSAGE, readMarker);
      conversation.off(Event.MESSAGE, messageUpdater);
      conversation.off(Event.LAST_DELIVERED_AT_UPDATE, receiptUpdateHandler);