// ...

const subscribeToNewChats = () => {
    chatsQuery.subscribeToMore({
      document: gql`
        subscription MessageSentSubscription {
          messageSent {
            id
            content
            from
            createdAt
          }
        }
      `,
      updateQuery: (previousData, { subscriptionData }) => {
        return {
          chats: [
            subscriptionData.data.messageSent,
            ...previousData.chats
          ].splice(0, 8)
        };
      }
    });
  };

// ...