Function useActiveScopeTracker

packages/react-aria/src/focus/FocusScope.tsx:580–611

(
  scopeRef: RefObject<Element[] | null>,
  restore?: boolean,
  contain?: boolean
)

}

function useActiveScopeTracker(
  scopeRef: RefObject<Element[] | null>,
  restore?: boolean,
  contain?: boolean
) {
  // tracks the active scope, in case restore and contain are both false.
  // if either are true, this is tracked in useRestoreFocus or useFocusContainment.
  useLayoutEffect(() => {
    if (restore || contain) {
      return;
    }

    let scope = scopeRef.current;
    const ownerDocument = getOwnerDocument(scope ? scope[0] : undefined);

    let onFocus = e => {
      let target = getEventTarget(e) as Element;
      if (isElementInScope(target, scopeRef.current)) {
        activeScope = scopeRef;
      } else if (!isElementInAnyScope(target)) {
        activeScope = null;
      }
    };

    ownerDocument.addEventListener('focusin', onFocus, false);
    scope?.forEach(element => element.addEventListener('focusin', onFocus, false));
    return () => {
      ownerDocument.removeEventListener('focusin', onFocus, false);
      scope?.forEach(element => element.removeEventListener('focusin', onFocus, false));
    };
  }, [scopeRef, restore, contain]);
}

function shouldRestoreFocus(scopeRef: ScopeRef) {
  let scope = focusScopeTree.getTreeNode(activeScope);