NavigateEvent: hasUAVisualTransition property

navigation.addEventListener("navigate", (event) => {
  // Some navigations, e.g. cross-origin navigations, we
  // cannot intercept. Let the browser handle those normally.
  if (!event.canIntercept) {
    return;
  }

  // Don't intercept fragment navigations or downloads.
  if (event.hashChange || event.downloadRequest !== null) {
    return;
  }

  event.intercept({
    handler() {
      // Fetch the new content
      const newContent = await fetchNewContent(event.destination.url, {
        signal: event.signal,
      });

      // 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);
      });
    },
  });
});