PopStateEvent: hasUAVisualTransition property

window.addEventListener("popstate", async (event) => {
  // Fetch the new content
  const newContent = await fetchNewContent(location.href);

  // The UA does not support View Transitions, or the UA
  // already provided a Visual Transition by itself (e.g. swipe back).
  // In either case, update the DOM directly
  if (!document.startViewTransition || event.hasUAVisualTransition) {
    doSinglePageAppNav(newContent);
    return;
  }

  // Update the content using a View Transition
  document.startViewTransition(() => {
    doSinglePageAppNav(newContent);
  });
});