router-core/not-found-and-errors

Add a notFoundComponent to your root route to render a global 404 for unmatched URLs. You can also set defaultNotFoundComponent on createRouter as a router-wide fallback for any route without its own handler.

Throw notFound() inside a loader or beforeLoad when a resource does not exist, and the nearest parent route with a notFoundComponent renders it. Pass a routeId option to target a specific parent route for handling.

The deprecated NotFoundRoute blocks notFound() and notFoundComponent from functioning, so remove it and use notFoundComponent instead. Also note that leaf routes without children cannot catch path-based not-found errors.

No, useLoaderData may be undefined in notFoundComponent because the loader may not have completed. Use Route.useParams, Route.useSearch, or Route.useRouteContext instead, or forward partial data via the data option on notFound().

Call router.invalidate() from your errorComponent to re-run the loader, which also resets the error boundary automatically. Calling reset() alone clears the boundary without re-running the loader.

Masking data is stored in location.state, so masked URLs are lost when shared or opened in a new tab. Masks survive local reloads by default unless you set unmaskOnReload on the mask, link, or router.