Fix Middleware Error in Remix

Remix Loader and Action Errors

Remix doesn't have traditional middleware — instead, loaders and actions serve that role. Errors in parent loaders cascade to child routes, and unhandled action errors break form submissions.

Parent Loader Errors

Parent route loaders run before child loaders. An error in the parent breaks all child routes:

// app/routes/_app.tsx (layout route)
// BAD — throws on auth failure, breaking all child routes
export async function loader({ request }: LoaderFunctionArgs) {
  const user = await getUser(request);
  if (!user) throw new Error('Not authenticated');
  return json({ user });
}

// GOOD — redirect instead of throwing
export async function loader({ request }: LoaderFunctionArgs) {
  const user = await getUser(request);
  if (!user) return redirect('/login');
  return json({ user });
}

Error Boundaries

Every route should have an error boundary:

export function ErrorBoundary() {
  const error = useRouteError();

  if (isRouteErrorResponse(error)) {
    return <div>Error {error.status}: {error.statusText}</div>;
  }

  return <div>Something went wrong</div>;
}

Action Error Handling

export async function action({ request }: ActionFunctionArgs) {
  const form = await request.formData();
  try {
    await createItem(Object.fromEntries(form));
    return redirect('/items');
  } catch (error) {
    // Return validation errors, don't throw
    return json(
      { error: error.message },
      { status: 400 }
    );
  }
}

Response Headers as Middleware

Use a headers export to set middleware-like response headers:

export function headers() {
  return { 'Cache-Control': 'max-age=300' };
}

Bugsly captures Remix loader and action errors with the full route hierarchy, making it clear which loader in the chain failed.