A sample React component that uses subscriptions along with Relay Modern

feed-subscription.jsx

fragment Feed_item on Photo {
    id
    creator {
      id
      name
    }
    photoUrl
}

class Feed extends React.Component {
  componentDidMount() {
    const addItemSubscription = graphql`
      subscription FeedAddSubscription { feedItemAdded { ...Feed_item } }
    `;
    requestSubscription(
      environment, // The relay environment created earlier
      {
        subscription: addItemSubscription,
        variables: null,
        onNext: (response) => {},
        onCompleted: () => {},
        onError: error => console.error(error),
        updater: (store) => {
          // application specific logic goes here
          const item = store.getRootField('feedItemAdded');
          const me = store.getRoot().getLinkedRecord('me');
          const feed = ConnectionHandler.getConnection(me, 'discover_feed');
          const edge = ConnectionHandler.createEdge(
            store,
            feed,
            item,
            'PhotoEdge',
          );
          ConnectionHandler.insertEdgeBefore(feed, edge);
          feed.setValue(feed.getValue('totalCount') + 1, 'totalCount');
        },
      }
    );
  }

  renderContent() {
    ...
  }

  render() {
    return this.renderContent();
  }
}