Function useFocusContainment

packages/react-aria/src/focus/FocusScope.tsx:335–475

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

}

function useFocusContainment(scopeRef: RefObject<Element[] | null>, contain?: boolean) {
  let focusedNode = useRef<FocusableElement>(undefined);

  let raf = useRef<ReturnType<typeof requestAnimationFrame>>(undefined);
  useLayoutEffect(() => {
    let scope = scopeRef.current;
    if (!contain) {
      // if contain was changed, then we should cancel any ongoing waits to pull focus back into containment
      if (raf.current) {
        cancelAnimationFrame(raf.current);
        raf.current = undefined;
      }
      return;
    }

    const ownerDocument = getOwnerDocument(scope ? scope[0] : undefined);

    // Handle the Tab key to contain focus within the scope
    let onKeyDown = e => {
      if (
        e.key !== 'Tab' ||
        e.altKey ||
        e.ctrlKey ||
        e.metaKey ||
        !shouldContainFocus(scopeRef) ||
        e.isComposing
      ) {
        return;
      }

      let focusedElement = getActiveElement(ownerDocument);
      let scope = scopeRef.current;
      if (!scope || !isElementInScope(focusedElement, scope)) {
        return;
      }

      let scopeRoot = getScopeRoot(scope);
      let walker = getFocusableTreeWalker(scopeRoot, {tabbable: true}, scope);
      if (!focusedElement) {
        return;
      }
      walker.currentNode = focusedElement;
      let nextElement = (
        e.shiftKey ? walker.previousNode() : walker.nextNode()
      ) as FocusableElement;
      if (!nextElement) {
        walker.currentNode = e.shiftKey
          ? scope[scope.length - 1].nextElementSibling!
          : scope[0].previousElementSibling!;
        nextElement = (e.shiftKey ? walker.previousNode() : walker.nextNode()) as FocusableElement;
      }

      e.preventDefault();
      if (nextElement) {
        focusElement(nextElement, true);
        if (nextElement instanceof getOwnerWindow(nextElement).HTMLInputElement) {
          nextElement.select();
        }