js

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({
    async handler() {
      if (myFramework.currentPage) {
        await myFramework.currentPage.transitionOut();
      }

      let { key } = event.destination;

      if (
        event.navigationType === "traverse" &&
        myFramework.previousPages.has(key)
      ) {
        await myFramework.previousPages.get(key).transitionIn();
      } else {
        // This will probably result in myFramework storing
        // the rendered page in myFramework.previousPages.
        await myFramework.renderPage(event.destination);
      }
    },
  });
});