blah.js

function handleKeyDown(event) {
  if (event.key === "Tab" && event.shiftKey) {
    if (shiftTabbedFromElementAfterTrigger(event)) {
      focusLastTabbableInPopover(event);
    } else if (shiftTabbedOutOfPopover(event)) {
      focusTriggerRef(event);
    } else if (shiftTabbedToBrowserChrome(event)) {
      disableTabbablesInPopover(event);
    }
  } else if (event.key === "Tab") {
    if (tabbedFromTriggerToPopover(event)) {
      focusFirstPopoverTabbable(event);
    } else if (tabbedOutOfPopover(event)) {
      focusTabbableAfterTrigger(event);
    } else if (tabbedToBrowserChrome(event)) {
      disableTabbablesInPopover(event);
    }
  }
}

useEffect(() => {
  doc.addEventListener("keydown", handleKeyDown);
  return () => doc.removeEventListener("keydown", handleKeyDown);
});