Data Loading

Data Loading

Setup

Basic loader returning data, consumed via useLoaderData:

// src/routes/posts.tsx
import { createFileRoute } from '@tanstack/react-router'

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  component: PostsComponent,
})

function PostsComponent() {
  const posts = Route.useLoaderData()
  return (
    <ul>
      {posts.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  )
}

In code-split components, use getRouteApi instead of importing Route:

import { getRouteApi } from '@tanstack/react-router'

const routeApi = getRouteApi('/posts')

function PostsComponent() {
  const posts = routeApi.useLoaderData()
  return <ul>{/* ... */}</ul>
}

Route Loading Lifecycle

The router executes this sequence on every URL/history update:

1. Route Matching (top-down)
   • route.params.parse
   • route.validateSearch
2. Route Pre-Loading (serial)
   • route.beforeLoad
   • route.onError → route.errorComponent
3. Route Loading (parallel)
   • route.component.preload?
   • route.loader
     • route.pendingComponent (optional)
     • route.component
   • route.onError → route.errorComponent

Key: beforeLoad runs before loader. beforeLoad for a parent runs before its children's beforeLoad. Throwing in beforeLoad prevents all children from loading.

Core Patterns

loaderDeps for Search-Param-Driven Cache Keys

Loaders don't receive search params directly. Use loaderDeps to declare which search params affect the cache key:

// src/routes/posts.tsx
import { createFileRoute } from '@tanstack/react-router'

export const Route = createFileRoute('/posts')({
  validateSearch: (search) => ({
    offset: Number(search.offset) || 0,
    limit: Number(search.limit) || 10,
  }),
  loaderDeps: ({ search: { offset, limit } }) => ({ offset, limit }),
  loader: ({ deps: { offset, limit } }) => fetchPosts({ offset, limit }),
})

When deps change, the route reloads regardless of staleTime.

SWR Caching Configuration

TanStack Router has built-in Stale-While-Revalidate caching keyed on the route's parsed pathname + loaderDeps.

Defaults:

• staleTime: 0 — data is always considered stale, reloads in background on re-match
• preloadStaleTime: 30 seconds — preloaded data won't be refetched for 30s
• gcTime: 30 minutes — unused cache entries garbage collected after 30min

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  staleTime: 10_000, // 10s: data considered fresh for 10 seconds
  gcTime: 5 * 60 * 1000, // 5min: garbage collect after 5 minutes
})

Disable SWR caching entirely:

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  staleTime: Infinity,
})

Globally:

const router = createRouter({
  routeTree,
  defaultStaleTime: Infinity,
})

Pending States (pendingComponent / pendingMs / pendingMinMs)

By default, a pending component shows after 1 second (pendingMs: 1000) and stays for at least 500ms (pendingMinMs: 500) to avoid flash.

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  pendingMs: 500,
  pendingMinMs: 300,
  pendingComponent: () => <div>Loading posts...</div>,
  component: PostsComponent,
})

Router Context with createRootRouteWithContext (Factory Pattern)

createRootRouteWithContext is a factory that returns a function. You must call it twice — the first call passes the generic type, the second passes route options:

// src/routes/__root.tsx
import { createRootRouteWithContext, Outlet } from '@tanstack/react-router'

interface MyRouterContext {
  auth: { userId: string }
  fetchPosts: () => Promise<Post[]>
}

// NOTE: double call — createRootRouteWithContext<Type>()({...})
export const Route = createRootRouteWithContext<MyRouterContext>()({
  component: () => <Outlet />,
})

Supply the context when creating the router:

// src/router.tsx
import { createRouter } from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

const router = createRouter({
  routeTree,
  context: {
    auth: { userId: '123' },
    fetchPosts,
  },
})

Consume in loaders and beforeLoad:

// src/routes/posts.tsx
export const Route = createFileRoute('/posts')({
  loader: ({ context: { fetchPosts } }) => fetchPosts(),
})

To pass React hook values into the router context, call the hook above RouterProvider and inject via the context prop:

import { RouterProvider } from '@tanstack/react-router'

function InnerApp() {
  const auth = useAuth()
  return <RouterProvider router={router} context={{ auth }} />
}

function App() {
  return (
    <AuthProvider>
      <InnerApp />
    </AuthProvider>
  )
}

Route-level context via beforeLoad:

export const Route = createFileRoute('/posts')({
  beforeLoad: ({ context }) => ({
    fetchPosts: context.fetchPosts,
  }),
  loader: ({ context: { fetchPosts } }) => fetchPosts(),
})

Keep the implementation SSR-safe when the router is used by TanStack Start. A relative fetch('/api/posts') works in a browser event handler, but Node and many server runtimes require an absolute URL during SSR. For app-internal data in Start, call a server function from the loader:

import { createServerFn } from '@tanstack/react-start'

const getPosts = createServerFn({ method: 'GET' }).handler(() => {
  return db.posts.findMany()
})

export const Route = createFileRoute('/posts')({
  loader: () => getPosts(),
})

Use a server route plus an origin-derived absolute URL only when the HTTP boundary itself is required. Do not hard-code the production origin.

Deferred Data Loading

Return unawaited promises from the loader for non-critical data. Use the Await component to render them:

import { createFileRoute, Await } from '@tanstack/react-router'

export const Route = createFileRoute('/posts/$postId')({
  loader: async ({ params: { postId } }) => {
    // Slow data — do NOT await
    const slowDataPromise = fetchComments(postId)
    // Fast data — await
    const post = await fetchPost(postId)

    return { post, deferredComments: slowDataPromise }
  },
  component: PostComponent,
})

function PostComponent() {
  const { post, deferredComments } = Route.useLoaderData()

  return (
    <div>
      <h1>{post.title}</h1>
      <Await
        promise={deferredComments}
        fallback={<div>Loading comments...</div>}
      >
        {(comments) => (
          <ul>
            {comments.map((c) => (
              <li key={c.id}>{c.body}</li>
            ))}
          </ul>
        )}
      </Await>
    </div>
  )
}

Invalidation After Mutations

router.invalidate() forces all active route loaders to re-run and marks all cached data as stale:

import { useRouter } from '@tanstack/react-router'

function AddPostButton() {
  const router = useRouter()

  const handleAdd = async () => {
    await createPost({ title: 'New post' })
    await router.invalidate({ sync: true })
  }

  return <button Post</button>
}

Use await router.invalidate({ sync: true }) when the next step requires refreshed loader data.

Treat the mutation and invalidation as one workflow. The mutation must persist before invalidation starts, and the loader must read from the same authoritative store. Verify create, update, and delete through the rendered route, including a fresh reload; local component state can hide a stale loader or non-persistent write.

Error Handling

import {
  createFileRoute,
  ErrorComponent,
  useRouter,
} from '@tanstack/react-router'

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  errorComponent: ({ error, reset }) => {
    const router = useRouter()

    if (error instanceof CustomError) {
      return <div>{error.message}</div>
    }

    return (
      <div>
        <ErrorComponent error={error} />
        <button
          => {
            // For loader errors, invalidate to re-run loader + reset boundary
            router.invalidate()
          }}
        >
          Retry
        </button>
      </div>
    )
  },
})

Loader Parameters

The loader function receives:

• params — parsed path params
• deps — object from loaderDeps
• context — merged parent + beforeLoad context
• abortController — cancelled when route unloads or becomes stale
• cause — 'enter', 'stay', or 'preload'
• preload — true during preloading
• location — current location object
• parentMatchPromise — promise of parent route match
• route — the route object itself

export const Route = createFileRoute('/posts/$postId')({
  loader: ({ params: { postId }, abortController }) =>
    fetchPost(postId, { signal: abortController.signal }),
})

Common Mistakes

CRITICAL: Assuming loaders only run on the server

TanStack Router is client-first. Loaders run on the client by default. They also run on the server when using TanStack Start for SSR, but the default mental model is client-side execution.

// WRONG — this will crash in the browser
export const Route = createFileRoute('/posts')({
  loader: async () => {
    const fs = await import('fs') // Node.js only!
    return JSON.parse(fs.readFileSync('...')) // fails in browser
  },
})

// CORRECT for an SPA — use a client-safe API helper
export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
})

Do NOT put database queries, filesystem access, or server-only code directly in loaders. In TanStack Start, put that work in a server function and call the function from the loader. Do not use a relative fetch('/api/...') in an SSR loader.

MEDIUM: Not understanding staleTime default is 0

Default staleTime is 0. This means data reloads in the background on every route re-match. This is intentional — it ensures fresh data. But if your data is expensive or static, set staleTime:

export const Route = createFileRoute('/posts')({
  loader: () => fetchPosts(),
  staleTime: 60_000, // Consider fresh for 1 minute
})

HIGH: Using reset() instead of router.invalidate() in error components

reset() only resets the error boundary UI. It does NOT re-run the loader. For loader errors, use router.invalidate() which re-runs loaders and resets the boundary:

// WRONG — resets boundary but loader still has stale error
function PostErrorComponent({ error, reset }) {
  return <button
}

// CORRECT — re-runs loader and resets the error boundary
function PostErrorComponent({ error }) {
  const router = useRouter()
  return <button => router.invalidate()}>Retry</button>
}

HIGH: Missing double parentheses on createRootRouteWithContext

createRootRouteWithContext<Type>() is a factory — it returns a function. Must call twice:

// WRONG — missing second call, passes options to the factory
const rootRoute = createRootRouteWithContext<{ auth: AuthState }>({
  component: RootComponent,
})

// CORRECT — factory()({options})
const rootRoute = createRootRouteWithContext<{ auth: AuthState }>()({
  component: RootComponent,
})

HIGH: Using React hooks in beforeLoad or loader

beforeLoad and loader are NOT React components. You cannot call hooks inside them. Use router context to inject values from hooks:

// WRONG — hooks cannot be called outside React components
export const Route = createFileRoute('/posts')({
  loader: () => {
    const auth = useAuth() // This will crash!
    return fetchPosts(auth.userId)
  },
})

// CORRECT — inject hook values via router context
// In your App component:
function InnerApp() {
  const auth = useAuth()
  return <RouterProvider router={router} context={{ auth }} />
}

// In your route:
export const Route = createFileRoute('/posts')({
  loader: ({ context: { auth } }) => fetchPosts(auth.userId),
})

HIGH: Property order affects TypeScript inference

Router infers types from earlier properties into later ones. Declaring beforeLoad after loader means context from beforeLoad is unknown in the loader:

// WRONG — context.user is unknown because beforeLoad declared after loader
export const Route = createFileRoute('/admin')({
  loader: ({ context }) => fetchData(context.user),
  beforeLoad: () => ({ user: getUser() }),
})

// CORRECT — validateSearch → loaderDeps → beforeLoad → loader
export const Route = createFileRoute('/admin')({
  beforeLoad: () => ({ user: getUser() }),
  loader: ({ context }) => fetchData(context.user),
})

HIGH: Returning entire search object from loaderDeps

// WRONG — loader re-runs on ANY search param change
loaderDeps: ({ search }) => search

// CORRECT — only re-run when page changes
loaderDeps: ({ search }) => ({ page: search.page })

Returning the whole search object means unrelated param changes (e.g., sortDirection, viewMode) trigger unnecessary reloads because deep equality fails on the entire object.

Tensions

• Client-first loaders vs SSR expectations: Loaders run on the client by default. When using SSR (TanStack Start), they run on both client and server. Browser-only APIs work by default but break under SSR. Server-only APIs (fs, db) break by default but work under Start server functions. See router-core/ssr/SKILL.md.
• Built-in SWR cache vs external cache coordination: Router has built-in caching. When using TanStack Query, set defaultPreloadStaleTime: 0 to avoid double-caching. See compositions/router-query/SKILL.md.

Cross-References

• See also: router-core/search-params/SKILL.md — loaderDeps consumes validated search params as cache keys
• See also: compositions/router-query/SKILL.md — for external cache coordination with TanStack Query