router-core-not-found-and-errors

name	router-core-not-found-and-errors
description	notFound() function, notFoundComponent, defaultNotFoundComponent, notFoundMode (fuzzy/root), errorComponent, CatchBoundary, CatchNotFound, isNotFound, NotFoundRoute (deprecated), route masking (mask option, createRouteMask, unmaskOnReload).
type	sub-skill
library	tanstack-router
library_version	1.166.2
requires	["router-core"]
sources	["TanStack/router:docs/router/guide/not-found-errors.md","TanStack/router:docs/router/guide/route-masking.md"]

Not Found and Errors

TanStack Router handles two categories of "not found": unmatched URL paths (automatic) and missing resources like a post that doesn't exist (manual via notFound()). Error boundaries are configured per-route via errorComponent.

CRITICAL: Do NOT use the deprecated NotFoundRoute. When present, notFound() and notFoundComponent will NOT work. Remove it and use notFoundComponent instead. CRITICAL: useLoaderData may be undefined inside notFoundComponent. Use useParams, useSearch, or useRouteContext instead.

Not Found Handling

Global 404: notFoundComponent on Root Route

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

export const Route = createRootRoute({
  component: () => <Outlet />,
  notFoundComponent: () => {
    return (
      <div>
        <h1>404 — Page Not Found</h1>
        <Link to="/">Go Home</Link>
      </div>
    )
  },
})

Router-Wide Default: defaultNotFoundComponent

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

const router = createRouter({
  routeTree,
  defaultNotFoundComponent: () => {
    return (
      <div>
        <p>Not found!</p>
        <Link to="/">Go home</Link>
      </div>
    )
  },
})

Per-Route 404: Missing Resources with notFound()

Throw notFound() in loader or beforeLoad when a resource doesn't exist. It works like redirect() — throw it to trigger the not-found boundary.

// src/routes/posts.$postId.tsx
import { createFileRoute, notFound } from '@tanstack/react-router'
import { getPost } from '../api'

export const Route = createFileRoute('/posts/$postId')({
  loader: async ({ params: { postId } }) => {
    const post = await getPost(postId)
    if (!post) throw notFound()
    return { post }
  },
  component: PostComponent,
  notFoundComponent: ({ data }) => {
    const { postId } = Route.useParams()
    return <p>Post "{postId}" not found</p>
  },
})

function PostComponent() {
  const { post } = Route.useLoaderData()
  return <h1>{post.title}</h1>
}

Targeting a Specific Route with notFound({ routeId })

You can force a specific parent route to handle the not-found error:

// src/routes/_layout/posts.$postId.tsx
import { createFileRoute, notFound } from '@tanstack/react-router'

export const Route = createFileRoute('/_layout/posts/$postId')({
  loader: async ({ params: { postId } }) => {
    const post = await getPost(postId)
    if (!post) throw notFound({ routeId: '/_layout' })
    return { post }
  },
})

Targeting Root Route with rootRouteId

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

export const Route = createFileRoute('/posts/$postId')({
  loader: async ({ params: { postId } }) => {
    const post = await getPost(postId)
    if (!post) throw notFound({ routeId: rootRouteId })
    return { post }
  },
})

notFoundMode: Fuzzy vs Root

fuzzy (default)

The router finds the nearest parent route with children and a notFoundComponent. Preserves as much parent layout as possible.

Given routes: __root__ → posts → $postId, accessing /posts/1/edit:

• <Root> renders
• <Posts> renders
• <Posts.notFoundComponent> renders (nearest parent with children + notFoundComponent)

root

All not-found errors go to the root route's notFoundComponent, regardless of matching:

const router = createRouter({
  routeTree,
  notFoundMode: 'root',
})

Error Handling

errorComponent Per Route

errorComponent receives error, info, and reset props. For loader errors, use router.invalidate() to re-run the loader — it automatically resets the error boundary.

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

export const Route = createFileRoute('/posts/$postId')({
  loader: async ({ params: { postId } }) => {
    const res = await fetch(`/api/posts/${postId}`)
    if (!res.ok) throw new Error('Failed to load post')
    return res.json()
  },
  component: PostComponent,
  errorComponent: PostErrorComponent,
})

function PostErrorComponent({
  error,
}: {
  error: Error
  info: { componentStack: string }
  reset: () => void
}) {
  const router = useRouter()

  return (
    <div>
      <p>Error: {error.message}</p>
      <button
        onClick={() => {
          // Invalidate re-runs the loader and resets the error boundary
          router.invalidate()
        }}
      >
        Retry
      </button>
    </div>
  )
}

function PostComponent() {
  const data = Route.useLoaderData()
  return <h1>{data.title}</h1>
}

Router-Wide Default Error Component

const router = createRouter({
  routeTree,
  defaultErrorComponent: ({ error }) => {
    const router = useRouter()
    return (
      <div>
        <p>Something went wrong: {error.message}</p>
        <button
          onClick={() => {
            router.invalidate()
          }}
        >
          Retry
        </button>
      </div>
    )
  },
})

Data in notFoundComponent

notFoundComponent cannot reliably use useLoaderData because the loader may not have completed. Safe hooks:

notFoundComponent: ({ data }) => {
  // SAFE — always available:
  const params = Route.useParams()
  const search = Route.useSearch()
  const context = Route.useRouteContext()

  // UNSAFE — may be undefined:
  // const loaderData = Route.useLoaderData()

  return <p>Item {params.id} not found</p>
}

To forward partial data, use the data option on notFound():

loader: async ({ params }) => {
  const partialData = await getPartialData(params.id)
  if (!partialData.fullResource) {
    throw notFound({ data: { name: partialData.name } })
  }
  return partialData
},
notFoundComponent: ({ data }) => {
  // data is typed as unknown — validate it
  const info = data as { name: string } | undefined
  return <p>{info?.name ?? 'Resource'} not found</p>
},

Route Masking

Route masking shows a different URL in the browser bar than the actual route being rendered. Masking data is stored in location.state and is lost when the URL is shared or opened in a new tab.

Imperative Masking on <Link>

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

function PhotoGrid({ photoId }: { photoId: string }) {
  return (
    <Link
      to="/photos/$photoId/modal"
      params={{ photoId }}
      mask={{
        to: '/photos/$photoId',
        params: { photoId },
      }}
    >
      Open Photo
    </Link>
  )
}

Imperative Masking with useNavigate

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

function OpenPhotoButton({ photoId }: { photoId: string }) {
  const navigate = useNavigate()

  return (
    <button
      onClick={() =>
        navigate({
          to: '/photos/$photoId/modal',
          params: { photoId },
          mask: {
            to: '/photos/$photoId',
            params: { photoId },
          },
        })
      }
    >
      Open Photo
    </button>
  )
}

Declarative Masking with createRouteMask

import { createRouter, createRouteMask } from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

const photoModalMask = createRouteMask({
  routeTree,
  from: '/photos/$photoId/modal',
  to: '/photos/$photoId',
  params: (prev) => ({ photoId: prev.photoId }),
})

const router = createRouter({
  routeTree,
  routeMasks: [photoModalMask],
})

Unmasking on Reload

By default, masks survive local page reloads. To unmask on reload:

// Per-mask
const mask = createRouteMask({
  routeTree,
  from: '/photos/$photoId/modal',
  to: '/photos/$photoId',
  params: (prev) => ({ photoId: prev.photoId }),
  unmaskOnReload: true,
})

// Per-link
<Link
  to="/photos/$photoId/modal"
  params={{ photoId }}
  mask={{ to: '/photos/$photoId', params: { photoId } }}
  unmaskOnReload
>
  Open Photo
</Link>

// Router-wide default
const router = createRouter({
  routeTree,
  unmaskOnReload: true,
})

Common Mistakes

1. HIGH: Using deprecated NotFoundRoute

// WRONG — NotFoundRoute blocks notFound() and notFoundComponent from working
import { NotFoundRoute } from '@tanstack/react-router'
const notFoundRoute = new NotFoundRoute({ component: () => <p>404</p> })
const router = createRouter({ routeTree, notFoundRoute })

// CORRECT — use notFoundComponent on root route
export const Route = createRootRoute({
  component: () => <Outlet />,
  notFoundComponent: () => <p>404</p>,
})

2. MEDIUM: Expecting useLoaderData in notFoundComponent

// WRONG — loader may not have completed
notFoundComponent: () => {
  const data = Route.useLoaderData() // may be undefined!
  return <p>{data.title} not found</p>
}

// CORRECT — use safe hooks
notFoundComponent: () => {
  const { postId } = Route.useParams()
  return <p>Post {postId} not found</p>
}

3. MEDIUM: Leaf routes cannot handle not-found errors

Only routes with children (and therefore an <Outlet>) can render notFoundComponent. Leaf routes (routes without children) will never catch not-found errors — the error bubbles up to the nearest parent with children.

// This route has NO children — notFoundComponent here will not catch
// unmatched child paths (there are no child paths to unmatch)
export const Route = createFileRoute('/posts/$postId')({
  // notFoundComponent here only works for notFound() thrown in THIS route's loader
  // It does NOT catch path-based not-founds
  notFoundComponent: () => <p>Not found</p>,
})

4. MEDIUM: Expecting masked URLs to survive sharing

Masking data lives in location.state (browser history). When a masked URL is copied, shared, or opened in a new tab, the masking data is lost. The browser navigates to the visible (masked) URL directly.

5. HIGH (cross-skill): Using reset() alone instead of router.invalidate()

// WRONG — reset() clears the error boundary but does NOT re-run the loader
function ErrorFallback({ error, reset }: { error: Error; reset: () => void }) {
  return <button onClick={reset}>Retry</button>
}

// CORRECT — invalidate re-runs loaders and resets the error boundary
function ErrorFallback({ error }: { error: Error; reset: () => void }) {
  const router = useRouter()
  return (
    <button
      onClick={() => {
        router.invalidate()
      }}
    >
      Retry
    </button>
  )
}

Cross-References

• router-core-data-loading — notFound() thrown in loaders interacts with error boundaries and loader data availability. errorComponent retry requires router.invalidate().
• router-core-type-safety — notFoundComponent data is typed as unknown; validate before use.