Inertia.js v3 — Prop Types Reference

Complete reference for all prop types: official PHP API, our bundle's API, behavior, and page object output.

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Closures (lazy evaluation)

// Closure: evaluated only when included (not when filtered by partial reload)
'users' => fn () => User::findAll(),

• Full render: ✅ resolved
• Partial (only/except): ✅ optionally
• Page object: props.users

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optional() — LazyProp

Official v3 API:

Inertia::optional(fn () => Permission::all())
// Chain with once:
Inertia::optional(fn () => Permission::all())->once()

Our bundle: $inertia->optional(fn () => ...) — canonical name. lazy() is a deprecated alias that still works.

• Full render: ❌ never included
• Partial with only: ['permissions']: ✅ resolved
• Partial without explicit only: ❌ skipped
• Page object: props (when included)

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always() — AlwaysProp

Inertia::always(fn () => auth()->user())

Our bundle: $inertia->always(fn () => ...)

• Full render: ✅ always
• Partial (only/except): ✅ always — bypasses all filters
• Page object: props

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defer() — DeferProp

Official v2 API:

// Single prop, default group
Inertia::defer(fn () => Permission::all())

// Named group (loads in parallel with other same-group props)
Inertia::defer(fn () => Team::all(), 'attributes')
Inertia::defer(fn () => Project::all(), 'attributes')

// Chain with once (our bundle: NOT YET IMPLEMENTED)
Inertia::defer(fn () => Stats::generate())->once()

// Chain with merge
Inertia::defer(fn () => User::paginate())->merge()
Inertia::defer(fn () => $data)->deepMerge()
Inertia::defer(fn () => $items)->prepend()
Inertia::defer(fn () => $items)->matchOn('id')
Inertia::defer(fn () => $items)->appendAt('data')
Inertia::defer(fn () => $items)->prependAt('data')

Our bundle: $inertia->defer(fn () => ..., 'groupName') — ->once() not yet supported.

• Full render: ❌ never in props — goes to deferredProps metadata only
• Deferred XHR (X-Inertia-Partial-Data: propKey): ✅ resolved
• Page object (full render): deferredProps: { "default": ["propKey"] }
• Page object (deferred XHR): props.propKey + merge metadata if applicable

DeferProp fluent merge methods (our bundle):

$inertia->defer(fn () => $items)
    ->merge()          // enables mergeProps
    ->deepMerge()      // enables deepMergeProps (also sets merge)
    ->prepend()        // enables prependProps (also sets merge)
    ->matchOn('id')    // adds to matchPropsOn as "propKey.id"
    ->appendAt('data') // adds "propKey.data" to mergeProps
    ->prependAt('data')// adds "propKey.data" to prependProps

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once() — OnceProp

Official v2 API:

// Basic
Inertia::once(fn () => Plan::all())

// Modifiers (chainable)
Inertia::once(fn () => ExchangeRate::all())->until(now()->addDay())  // expiry
Inertia::once(fn () => Plan::all())->until(3600)                    // seconds from now
Inertia::once(fn () => Role::all())->as('roles')                    // alias key
Inertia::once(fn () => Plan::all())->fresh()                        // force re-resolve
Inertia::once(fn () => Plan::all())->fresh($condition)              // conditional

// Global sharing
Inertia::shareOnce('countries', fn () => Country::all())
Inertia::shareOnce('countries', fn () => Country::all())->until(now()->addDay())

Our bundle: $inertia->once(fn () => ...) — all modifiers implemented.

• Full render: ✅ resolved + metadata in onceProps
• Subsequent XHR (client sends X-Inertia-Except-Once-Props: plans): ❌ value skipped, metadata always emitted
• Partial reload: X-Inertia-Except-Once-Props is ignored — follows normal $only/$except
• Page object: props.plans (when included) + onceProps.plans: { prop: "plans", expiresAt: null }

OnceProp metadata always emitted even when value is absent (fix 2026-04-02): Client needs onceProps[key] to know it should reinject from cache.

expiresAt: Unix timestamp (seconds) or null. Client auto-invalidates when expired. fresh: true: included in metadata when ->fresh() is set. Alias: onceProps key = alias, prop field = original key.

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merge() / deepMerge() — MergeProp

Official v2 API:

// Append at root (default)
Inertia::merge($items)

// Prepend at root
Inertia::merge($items)->prepend()

// Append at sub-path
Inertia::merge(User::paginate())->append('data')
Inertia::merge($data)->append(['notifications', 'activities'])
Inertia::merge($data)->append('data', matchOn: 'id')
Inertia::merge($data)->append(['users.data' => 'id', 'messages' => 'uuid'])

// Deep merge
Inertia::deepMerge($data)->matchOn('messages.id')

// Combine
Inertia::merge($data)->once()
Inertia::defer(fn() => $data)->deepMerge()

Our bundle:

// Constructor params (equivalent, different style)
$inertia->merge(fn() => $items)
$inertia->merge(fn() => $items, prepend: true)
$inertia->merge(fn() => $data, deep: true)
$inertia->merge(fn() => $data, matchOn: 'id')
$inertia->merge(fn() => $data, appendsAtPaths: 'data')
$inertia->merge(fn() => $data, prependsAtPaths: 'data')
// Missing: $inertia->deepMerge() factory

• Full render: ✅ resolved
• Partial: follows $only/$except
• Only merges during partial reloads — full page visits always replace
• Reset via client: router.reload({ reset: ['posts'] }) → server receives X-Inertia-Reset: posts

Page object fields:

{ "mergeProps": ["posts"],        // root append, or "posts.data" for sub-path
  "prependProps": ["notifications"],
  "deepMergeProps": ["conversations"],
  "matchPropsOn": ["posts.id", "notifications.id"] }

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scroll() — ScrollProp

Official v2 API (Laravel):

// Auto-detects pagination metadata from Laravel paginators
Inertia::scroll(User::paginate(20))
Inertia::scroll(User::simplePaginate(20))
Inertia::scroll(User::cursorPaginate(20))
Inertia::scroll(UserResource::collection(User::paginate(20)))

// Custom wrapper key (defaults to 'data')
Inertia::scroll($data, wrapper: 'items')

// Custom metadata
Inertia::scroll($data, metadata: new CustomScrollMetadata())

// Multiple paginators (custom pageName avoids query param conflicts)
'users' => Inertia::scroll(fn() => User::paginate(pageName: 'users')),
'orders' => Inertia::scroll(fn() => Order::paginate(pageName: 'orders')),

Our bundle (Symfony — no auto-detection, explicit pagination values):

$inertia->scroll(
    fn () => $posts,        // callback returns plain array (not paginator object)
    pageName: 'page',       // query param name (default: 'page')
    nextPage: $nextPage,    // int|string|null
    previousPage: $prevPage,
    currentPage: $page,
    prepend: false,
)

// Optional: defer
$inertia->scroll(fn () => $posts, nextPage: 2)->defer()
$inertia->scroll(fn () => $posts, nextPage: 2)->defer('myGroup')

Design difference vs Laravel:

• Laravel emits mergeProps: ["posts.data"] (sub-path within paginator)
• Our bundle emits mergeProps: ["posts"] (root merge)
• Our callback should return a plain array, not a paginator object

Page object:

{ "mergeProps": ["posts"],
  "scrollProps": { "posts": { "pageName": "page", "previousPage": null, "nextPage": 2, "currentPage": 1 } } }

Client sends X-Inertia-Infinite-Scroll-Merge-Intent: prepend|append to override the static prepend flag. Client sends X-Inertia-Reset: posts to reset before merging (handled via $reset array in collectScrollProps).

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flash() — Flash Data

Official v3 API (Laravel):

Inertia::flash('message', 'User created!');
return back();

// Chainable
return Inertia::flash('newUserId', $user->id)->back();
return Inertia::render('Page', $props)->flash('highlight', $id);

Our bundle: $inertia->flash(string $key, mixed $value): void (returns void, not chainable).

v3 IMPORTANT: Flash is a TOP-LEVEL page object field, NOT inside props.

• v2: props.flash.key → v3: page.flash.key (top-level)
• Omitted when empty; client defaults to {}
• Client fires inertia:flash event when flash contains data
• Not stored in browser history state (client clears flash: {} before pushState)

Current bundle status: Our bundle currently puts flash inside props.flash — this needs to be moved to a top-level flash field in buildPageObject(). Tracked as an open gap.

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errors Prop — Invariant

errors is ALWAYS present in props, default: []
Even if a DeferProp or LazyProp was passed as 'errors', the key always exists.
AlwaysProp wrapping errors in Laravel middleware — our bundle guarantees it in InertiaResponse::build().

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Server-Side Prop Sharing

// Share across all pages
$inertia->share('appName', 'MyApp');
$inertia->share('auth.user', fn () => $user?->toArray());

// Share once (cached client-side)
$inertia->shareOnce('countries', fn () => $this->countryRepo->findAll());
// wraps plain values/closures in OnceProp automatically

// Per-request: in a controller
return $inertia->render('Users/Index', [
    'users' => fn () => $this->userRepo->findAll(),
]);