NavigateEvent: canIntercept property

The canIntercept read-only property of the NavigateEvent interface returns true if the navigation can be intercepted and have its URL rewritten, or false otherwise

There are several rules around when a navigation can be intercepted. For example:

• You can't intercept cross-origin navigations.
• You can intercept http or https URLs if only the path, query, and fragment portions of the new URL differ from the current URL.
• You can intercept file URLs if only the query and fragment portions of the new URL differ.
• For other URL types you can intercept the navigation if only the fragment portion differs.

See the spec for more explanation on when a Document can have its URL rewritten, including a table of examples.

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() {
      if (event.formData) {
        processFormDataAndUpdateUI(event.formData, event.signal);
      } else {
        doSinglePageAppNav(event.destination, event.signal);
      }
    },
  });
});