Inertia Rails Pages

Page components, layouts, navigation, and client-side APIs.

Before building a page, ask:

Does this page need a layout? → Use persistent layout (React: Page.layout = ...; Vue: defineOptions({ layout }); Svelte: module script export) — wrapping in JSX/template remounts on every navigation, losing scroll position, audio playback, and component state
Does UI state come from the URL? → Change BOTH controller (read params, pass as prop) AND component (derive from prop, no useState/useEffect) — use router.get to update URL
Need to refresh data without navigation? → router.reload({ only: [...] }) — never useEffect + fetch
Need to update a prop without server round-trip? → router.replaceProp — no fetch, no reload

NEVER:

Parse window.location.search or use useSearchParams — derive URL state from controller props
Use useState/useEffect to sync URL ↔ React state — the controller passes URL-derived data as props; the component just reads them
Pass arguments to <Deferred> render function — {(data) => ...} does NOT work; child reads via usePage()
Access usePage().props.flash — flash is top-level: usePage().flash
Wrap layout in JSX return for persistence — use Page.layout = ... or global layout inside createInertiaApp's resolve callback

Page Component Structure

Pages are default exports receiving controller props as function arguments. Use type Props = { ... } (not interface — causes TS2344 in React). Vue uses defineProps<T>(), Svelte uses let { ... } = $props().

type Props = {
  posts: Post[]
}

export default function Index({ posts }: Props) {
  return <PostList posts={posts} />
}

Persistent Layouts

Layouts persist across navigations — no remounting, preserving scroll, audio, etc.

import { AppLayout } from '@/layouts/app-layout'

export default function Show({ course }: Props) {
  return <CourseContent course={course} />
}

// Single layout
Show.layout = (page: React.ReactNode) => <AppLayout>{page}</AppLayout>

Default layout in entrypoint:

// app/frontend/entrypoints/inertia.tsx
resolve: async (name) => {
  const page = await pages[`../pages/${name}.tsx`]()
  page.default.layout ??= (page: React.ReactNode) => <AppLayout>{page}</AppLayout> // default if not set
  return page
}

Navigation

`<Link>` and `router`

Use <Link href="..."> for internal navigation (not <a>) and router.get/post/patch/delete for programmatic navigation. Key non-obvious features:

// Prefetching — preloads page data on hover
<Link href="/users" prefetch>Users</Link>
<Link href="/users" prefetch cacheFor="30s">Users</Link>

// Prefetch with cache tags — invalidate after mutations
<Link href="/users" prefetch cacheTags="users">Users</Link>

// Programmatic prefetch (e.g., likely next destination)
router.prefetch('/settings', {}, { cacheFor: '1m' })

// Partial reload — refresh specific props without navigation
router.reload({ only: ['users'] })

Full router API, visit options, and event callbacks are in references/navigation.md — see loading trigger below.

Client-Side Prop Helpers

Update props without a server round-trip:

// Replace a single prop (dot notation supported)
router.replaceProp('show_modal', false)
router.replaceProp('user.name', 'Jane Smith')

// With callback (receives current value + all props)
router.replaceProp('count', (current) => current + 1)

// Append/prepend to array props
router.appendToProp('messages', { id: 4, text: 'New' })
router.prependToProp('notifications', (current, props) => ({
  id: Date.now(),
  message: `Hello ${props.auth.user.name}`,
}))

These are shortcuts to router.replace() with preserveScroll and preserveState automatically set to true.

router.replaceProp vs router.reload: Use router.replaceProp for client-only state changes (toggling a modal, incrementing a counter) — no server round-trip. Use router.reload when you need fresh data from the server (updated records, recalculated stats).

URL-Driven State (Dialogs, Tabs, Filters)

URL state = server state = props. ALWAYS implement both sides:

Controller — read params and pass as a prop
Component — derive UI state from that prop (no useState, no useEffect)
Update — router.get with query params to change URL (triggers server round-trip, new props arrive)

NEVER use useState + useEffect to sync URL ↔ dialog/tab/filter state. The server is the single source of truth — the component just reads props.

# Step 1: Controller reads params, passes as prop
def index
  render inertia: {
    users: User.all,
    selected_user_id: params[:user_id]&.to_i
  }
end

// Step 2+3: Derive state from props, router.get to update URL

type Props = {
  users: User[]
  selected_user_id: number | null  // from controller
}

export default function Index({ users, selected_user_id }: Props) {
  // Derive — no useState, no useEffect, no window.location parsing
  const selectedUser = selected_user_id
    ? users.find(u => u.id === selected_user_id)
    : null

  const openDialog = (id: number) =>
    router.get('/users', { user_id: id }, {
      preserveState: true,
      preserveScroll: true,
    })

  const closeDialog = () =>
    router.get('/users', {}, {
      preserveState: true,
      preserveScroll: true,
    })

  return (
    <Dialog open={!!selectedUser} onOpenChange={(open) => !open && closeDialog()}>
      <DialogContent>{/* ... */}</DialogContent>
    </Dialog>
  )
}

Why not useEffect? When router.get('/users', { user_id: 5 }) fires, Inertia makes a request to the server → controller runs with params[:user_id] = 5 → returns new props with selected_user_id: 5 → component re-renders with the dialog open. The cycle is: URL → server → props → render. Parsing window.location client-side duplicates what the server already does.

Shared Props

Shared props (auth, flash) are typed globally via InertiaConfig (see inertia-rails-typescript skill) — page components only type their OWN props:

type Props = {
  users: User[]         // page-specific only
  // auth is NOT here — typed globally via InertiaConfig
}

export default function Index({ users }: Props) {
  const { props, flash } = usePage()
  // props.auth typed via InertiaConfig, flash.notice typed via InertiaConfig
  return <UserList users={users} />
}

Flash Access

Flash is top-level on the page object, NOT inside props — this is the #1 flash mistake. Flash config is in inertia-rails-controllers; toast UI is in shadcn-inertia.

// BAD:  usePage().props.flash   ← WRONG, flash is not in props
// GOOD: usePage().flash         ← flash.notice, flash.alert

`<Deferred>` Component

Renders fallback until deferred props arrive. Children can be plain ReactNode or () => ReactNode render function. Either way, the child reads the deferred prop from page props via usePage() — the render function receives no arguments.

import { Deferred } from '@inertiajs/react'

export default function Dashboard({ basic_stats }: Props) {
  return (
    <>
      <QuickStats data={basic_stats} />
      <Deferred data="detailed_stats" fallback={<Spinner />}>
        <DetailedStats />
      </Deferred>
    </>
  )
}

// Also valid — render function (no args, child still reads from usePage):
// <Deferred data="stats" fallback={<Spinner />}>
//   {() => <Stats />}
// </Deferred>

// BAD — render function does NOT receive data as argument:
// <Deferred data="stats">{(data) => <Stats data={data} />}</Deferred>

`<InfiniteScroll>` Component

Automatic infinite scroll — loads next pages as user scrolls down. Pairs with InertiaRails.scroll on the server (see inertia-rails-controllers):

import { InfiniteScroll } from '@inertiajs/react'

export default function Index({ posts }: Props) {
  return (
    <InfiniteScroll data="posts" loading={() => <Spinner />}>
      {posts.map(post => <PostCard key={post.id} post={post} />)}
    </InfiniteScroll>
  )
}

Props: data (prop name), loading (fallback), manual (button instead of auto), manualAfter={3} (auto for first 3 pages, then button), preserveUrl (don't update URL).

`<WhenVisible>` Component

Loads data when element enters viewport. Use for lazy sections (comments, related items), NOT for infinite scroll (use <InfiniteScroll> above):

import { WhenVisible } from '@inertiajs/react'

<WhenVisible data="comments" fallback={<Spinner />}>
  <CommentsList />
</WhenVisible>

Troubleshooting

Symptom	Cause	Fix
Layout remounts on every navigation	Wrapping layout in JSX return instead of `Page.layout`	Use persistent layout
`Deferred` children never render	Render function expects args `{(data) => ...}`	Render function receives NO arguments — use `{() => <Child />}` or plain `<Child />`. Child reads prop via `usePage()`
Flash is `undefined`	Accessing `usePage().props.flash`	Flash is top-level: `usePage().flash`, not inside `props`
URL state lost on navigation	Parsing `window.location` in useEffect	Derive from props — controller reads `params` and passes as prop
`WhenVisible` never triggers	Element not in viewport or prop name wrong	`data` must match a prop name the controller provides on partial reload
Component state resets on `router.get`	Missing `preserveState: true`	Add `preserveState: true` to visit options for filter/sort/tab changes
Scroll jumps to top after form submit	Missing `preserveScroll`	Add `preserveScroll: true` to the visit or form options

Related Skills

Flash config → inertia-rails-controllers (flash_keys)
Flash toast UI → shadcn-inertia (Sonner + useFlash)
Shared props typing → inertia-rails-typescript (InertiaConfig)
Deferred server-side → inertia-rails-controllers (InertiaRails.defer)
URL-driven dialogs → shadcn-inertia (Dialog component)

Vue / Svelte

All examples above use React syntax. For Vue 3 or Svelte equivalents:

Vue 3: references/vue.md — defineProps, usePage() composable, scoped slots for <Deferred>/<WhenVisible>/<InfiniteScroll>, defineOptions({ layout }) for persistent layouts
Svelte: references/svelte.md — $props(), $page store, {#snippet} syntax for <Deferred>/<WhenVisible>/<InfiniteScroll>, <svelte:head> instead of <Head>, module script layout export

MANDATORY — READ THE MATCHING FILE when the project uses Vue or Svelte. The concepts and NEVER rules above apply to all frameworks, but code syntax differs.

References

MANDATORY — READ ENTIRE FILE when implementing event callbacks (onBefore, onStart, onProgress, onFinish, onCancel), client-side flash, or scroll management: references/navigation.md (~200 lines) — full callback API, router.flash(), scroll regions, and history encryption.

MANDATORY — READ ENTIRE FILE when implementing nested layouts, conditional layouts, or layout-level data sharing: references/layouts.md (~180 lines) — nested layout patterns, layout props, and default layout configuration.

Do NOT load references for basic <Link>, router.visit, or single-level layout usage — the examples above are sufficient.

inertia-rails-pages