_app.tsx

useFeatureValue

const growthbook = new GrowthBook({
  apiHost: '<https://cdn.growthbook.io>',
  clientKey: growthbookClientKey,
  enableDevMode: !(isBeta() || isProduction()),
  trackingCallback: (experiment, result) => {
    sendEvent(
      eventCategory.AB_TEST,
      eventAction.EXPERIMENT_VIEWED,
      experiment.key,
      result.variationId,
      {
        experimentId: experiment.key,
        variationId: result.variationId,
      },
    );
  },
});

const EdpressoUserActions = ({}) => {
  const loggedIn = useTypedSelector(
    (state) => !!<http://state.user.info?.data?.user_id|state.user.info?.data?.user_id>,
  );

  const feature_value = useFeatureValue('edpresso_aa_test', 'fallback');
  console.log('feature_value', feature_value);

  React.useEffect(() => {
    const loadFeatures = async () => {
      await growthbook.loadFeatures({
        autoRefresh: true,
        timeout: 2000,
      });
    };
    try {
      loadFeatures();
    } catch (error) {
      sendErrorEvent(error);
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  React.useEffect(() => {
    const sessionId =
      !loggedIn && !document.cookie.match(/_ga=(.+?);/)
        ? ''
        : document.cookie
            .match(/_ga=(.+?);/)[1]
            .split('.')
            .slice(-2)
            .join('.');

    growthbook.setAttributes({
      loggedIn: loggedIn,
      id: sessionId,
    });
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [loggedIn]);

.....}