probo / rules

---
description: Named exports for components; default export only for lazy() bundle entries
globs: "**/*.tsx"
alwaysApply: false
---

# Named exports; `export default` only for lazy() entries

React components use **named exports**. `export default` is reserved as an
exception **only** for the component a router/`lazy()` imports as a bundle entry,
because `lazy(() => import("./X"))` resolves the module's default export.

In the Loader + Page/Layout pattern this means exactly **one** default export per
chain — the Loader (the `lazy()` target). The Page/Layout it renders is imported
**directly by the Loader**, not through `lazy()`, so it must be a named export.

```tsx
// GOOD — Loader is the lazy() entry → default export
// MainLayoutLoader.tsx
import { MainLayout, mainLayoutQuery } from "./MainLayout";
export default function MainLayoutLoader() { /* useQueryLoader → <MainLayout /> */ }

// GOOD — Layout/Page imported directly by the Loader → named export
// MainLayout.tsx
export const mainLayoutQuery = graphql`query MainLayoutQuery { ...TopBar_query }`;
export function MainLayout({ queryRef }: MainLayoutProps) { /* usePreloadedQuery */ }

// routes.tsx — only the Loader is referenced by lazy()
Component: lazy(() => import("#/pages/MainLayoutLoader")),
```

```tsx
// BAD — Page/Layout defaulted even though the Loader (not lazy) imports it
// MainLayout.tsx
export default function MainLayout(/* ... */) {}
// MainLayoutLoader.tsx
import MainLayout, { mainLayoutQuery } from "./MainLayout";
```

A page with no loader (no Relay data) that `lazy()` imports directly is itself
the bundle entry, so it keeps the `export default`. The rule is about *who
`lazy()` imports*, not about the "Page" vs "Layout" label.

See `contrib/claude/react-components.md` (File and export) and
`contrib/claude/app-arborescence.md`.

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