Repository: storybookjs/storybook
File: code/core/src/manager/App.tsx (TypeScript)

Code before:
  setManagerLayoutState: ComponentProps<typeof Layout>['setManagerLayoutState'];
  pages: Addon_PageType[];
  hasTab: boolean;
};

export const App = ({ managerLayoutState, setManagerLayoutState, pages, hasTab }: Props) => {
  const { setMobileAboutOpen } = useLayout();

  const { enableShortcuts = true } = addons.getConfig();
  useEffect(() => {
    document.body.setAttribute('data-shortcuts-enabled', enableShortcuts ? 'true' : 'false');
  }, [enableShortcuts]);

  useEffect(() => {
    const rootElement = document.getElementById('root');
    if (!rootElement) {
      return;
    }

    const observer = new MutationObserver((mutations) => {
      mutations.forEach((mutation) => {
        if (mutation.type === 'attributes' && mutation.attributeName === 'inert') {
          const hasInert = rootElement.hasAttribute('inert');
          addons.getChannel().emit('managerFocusTrapChange', hasInert);
        }
      });
    });

    observer.observe(rootElement, {
      attributes: true,
      attributeFilter: ['inert'],
    });

    return () => observer.disconnect();
  }, []);

  return (
    <>
      <Global styles={createGlobal} />
      <Layout
        hasTab={hasTab}
        managerLayoutState={managerLayoutState}
        setManagerLayoutState={setManagerLayoutState}
        slotMain={<Preview id="main" withLoader />}
        slotSidebar={<Sidebar onMenuClick={() => setMobileAboutOpen((state) => !state)} />}
        slotPanel={<Panel />}
        slotPages={pages.map(({ id, render: Content }) => (
          <Content key={id} />
        ))}
      />
    </>

Review comment (suggestion):
Technically this is the correct way do handle the callback value, but we don't really need the `forEach` nor the `if` check, since we're only observing a single element and we're using `attributeFilter`, so we know by definition that `mutations` will be a single item `{ type: 'attributes', attributeName: 'inert' }`.

Code after:
  managerLayoutState: ComponentProps<typeof Layout>['managerLayoutState'];
  setManagerLayoutState: ComponentProps<typeof Layout>['setManagerLayoutState'];
  pages: Addon_PageType[];
  hasTab: boolean;
};

export const App = ({ managerLayoutState, setManagerLayoutState, pages, hasTab }: Props) => {
  const { setMobileAboutOpen } = useLayout();

  /**
   * Lets us tell the UI whether or not keyboard shortcuts are enabled, in places where it's not
   * convenient to load the addons singleton to figure it out.
   */
  const { enableShortcuts = true } = addons.getConfig();
  useEffect(() => {
    document.body.setAttribute('data-shortcuts-enabled', enableShortcuts ? 'true' : 'false');
  }, [enableShortcuts]);

  /**
   * Detects when our component library has enabled a focus trap. By convention, react-aria sets the
   * document root to `inert` when a focus trap is enabled. We observe that attribute and inform the
   * preview iframe when to respect the focus trap, via a channel event. This is necessary because
   * inert is no longer propagated into iframes as per https://github.com/whatwg/html/issues/7605,
   * and the replacement permission policy is not yet widely available
   * (https://github.com/w3c/webappsec-permissions-policy/issues/273).
   */
  useEffect(() => {
    const rootElement = document.getElementById('root');
    if (!rootElement) {
      return;
    }

    const observer = new MutationObserver(() => {
      const hasInert = rootElement.hasAttribute('inert');
      addons.getChannel().emit(Events.MANAGER_INERT_ATTRIBUTE_CHANGED, hasInert);
    });

    observer.observe(rootElement, {
      attributes: true,
      attributeFilter: ['inert'],
    });

    return () => observer.disconnect();
  }, []);

  return (
    <>
      <Global styles={createGlobal} />
      <Layout
        hasTab={hasTab}
        managerLayoutState={managerLayoutState}