How to use the @material/tab-bar.MDCTabBarFoundation.strings function in @material/tab-bar

getTabElements(): Element[] | null {
    return [].slice.call(
      this.root.ref &&
        this.root.ref.querySelectorAll(MDCTabBarFoundation.strings.TAB_SELECTOR)
    );
  }

getFocusedTabIndex: () => {
          const tabElements: Element[] = [].slice.call(
            rootEl.ref?.querySelectorAll(
              MDCTabBarFoundation.strings.TAB_SELECTOR
            )
          );
          const activeElement = document.activeElement as Element;
          return tabElements ? tabElements.indexOf(activeElement) : -1;
        },
        getIndexOfTabById: (id: string) => {