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Components

TanStack Start provides specialized React components for building full-stack applications.

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StartClient

StartClient is the root client component that hydrates your application in the browser.

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Usage

// src/entry-client.tsx
import { StartClient } from '@tanstack/react-start'
import { hydrateRoot } from 'react-dom/client'

hydrateRoot(document.getElementById('root')!, <StartClient />)

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How It Works

The StartClient component:
  1. Calls hydrateStart() to restore the router state from the server
  2. Wraps your application with RouterProvider
  3. Uses Await to handle the hydration promise
  4. Signals when hydration is complete for cleanup
import { Await, RouterProvider } from '@tanstack/react-router'
import { hydrateStart } from './hydrateStart'

let hydrationPromise: Promise<AnyRouter> | undefined

export function StartClient() {
  if (!hydrationPromise) {
    hydrationPromise = hydrateStart()
  }

  return (
    <Await
      promise={hydrationPromise}
      children={(router) => <RouterProvider router={router} />}
    />
  )
}

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StartServer

StartServer is the root server component used during server-side rendering.

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Usage

// src/entry-server.tsx
import { StartServer } from '@tanstack/react-start/server'
import { createMemoryHistory } from '@tanstack/react-router'

export async function render(request: Request) {
  const router = createRouter()
  const memoryHistory = createMemoryHistory({
    initialEntries: [new URL(request.url).pathname],
  })
  
  router.update({ history: memoryHistory })
  await router.load()
  
  return <StartServer router={router} />
}

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How It Works

StartServer is a thin wrapper around RouterProvider for the server: 
import { RouterProvider } from '@tanstack/react-router'
import type { AnyRouter } from '@tanstack/router-core'

export function StartServer<TRouter extends AnyRouter>(props: {
  router: TRouter
}) {
  return <RouterProvider router={props.router} />
}

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Entry Points

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Client Entry

Your client entry file renders the StartClient component: 
// src/entry-client.tsx
import { StartClient } from '@tanstack/react-start'
import { hydrateRoot } from 'react-dom/client'

hydrateRoot(
  document.getElementById('root')!,
  <StartClient />
)

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Server Entry

Your server entry file uses StartServer for SSR: 
// src/entry-server.tsx
import { renderToString } from 'react-dom/server'
import { StartServer } from '@tanstack/react-start/server'
import { createMemoryHistory } from '@tanstack/react-router'
import { createRouter } from './router'

export async function render(request: Request) {
  const router = createRouter()
  const history = createMemoryHistory({
    initialEntries: [new URL(request.url).pathname],
  })
  
  router.update({ history })
  await router.load()
  
  const html = renderToString(<StartServer router={router} />)
  
  return new Response(html, {
    headers: { 'Content-Type': 'text/html' },
  })
}

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Hydration

The hydration process seamlessly transfers state from server to client.

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hydrateStart

The hydrateStart function restores the router instance on the client: 
import { hydrateStart } from '@tanstack/react-start/client'

// Called by StartClient
const router = await hydrateStart()

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Hydration Flow

  1. Server: Router state is serialized and embedded in the HTML
  2. Client: hydrateStart() deserializes the state
  3. Client: Router is initialized with the restored state
  4. Client: React hydrates the DOM without re-rendering
  5. Cleanup: Hydration signal triggers any necessary cleanup

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Router Integration

Start components integrate with TanStack Router components: 
import {
  Link,
  Outlet,
  RouterProvider,
  createRootRoute,
  createRoute,
  createRouter,
} from '@tanstack/react-router'
import { StartClient } from '@tanstack/react-start'

const rootRoute = createRootRoute({
  component: () => (
    <div>
      <nav>
        <Link to="/">Home</Link>
        <Link to="/about">About</Link>
      </nav>
      <Outlet />
    </div>
  ),
})

const indexRoute = createRoute({
  getParentRoute: () => rootRoute,
  path: '/',
  component: () => <h1>Home</h1>,
})

const routeTree = rootRoute.addChildren([indexRoute])
const router = createRouter({ routeTree })

// In your app
<StartClient />

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Scripts Component

The Scripts component injects client bundles into your HTML: 
import { Scripts } from '@tanstack/react-router'

function RootDocument({ children }: { children: React.ReactNode }) {
  return (
    <html>
      <head>
        <meta charSet="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1" />
      </head>
      <body>
        {children}
        <Scripts />
      </body>
    </html>
  )
}

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Head Management

Manage document head with HeadContent: 
import { HeadContent, createRootRoute } from '@tanstack/react-router'

export const Route = createRootRoute({
  head: () => ({
    meta: [
      { charSet: 'utf-8' },
      { name: 'viewport', content: 'width=device-width, initial-scale=1' },
      { name: 'description', content: 'My TanStack Start app' },
    ],
    links: [
      { rel: 'stylesheet', href: '/styles/app.css' },
      { rel: 'icon', href: '/favicon.ico' },
    ],
  }),
  component: () => (
    <html>
      <head>
        <HeadContent />
      </head>
      <body>
        <Outlet />
      </body>
    </html>
  ),
})

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Streaming

Stream HTML and data to the client: 
import { renderToPipeableStream } from 'react-dom/server'
import { StartServer } from '@tanstack/react-start/server'

export async function render(request: Request) {
  const router = createRouter()
  // ... setup router
  
  return new Promise((resolve) => {
    const { pipe } = renderToPipeableStream(
      <StartServer router={router} />,
      {
        onShellReady() {
          const stream = new TransformStream()
          pipe(stream.writable)
          resolve(new Response(stream.readable, {
            headers: { 'Content-Type': 'text/html' },
          }))
        },
      }
    )
  })
}

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Deferred Data

Use Await and Suspense for deferred data loading: 
import { Suspense } from 'react'
import { Await, createFileRoute } from '@tanstack/react-router'
import { fetchData } from '~/utils/data'

export const Route = createFileRoute('/data')({  
  loader: async () => ({
    // Deferred - resolves after initial render
    deferredData: fetchData(),
  }),
  component: DataPage,
})

function DataPage() {
  const { deferredData } = Route.useLoaderData()
  
  return (
    <Suspense fallback={<div>Loading data...</div>}>
      <Await promise={deferredData}>
        {(data) => <div>{data}</div>}
      </Await>
    </Suspense>
  )
}

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Error Boundaries

Handle errors with error boundaries: 
import { ErrorComponent, createRootRoute } from '@tanstack/react-router'

export const Route = createRootRoute({
  errorComponent: ({ error }) => (
    <div>
      <h1>Something went wrong</h1>
      <pre>{error.message}</pre>
    </div>
  ),
})

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Not Found

Handle 404 errors: 
import { createRootRoute } from '@tanstack/react-router'

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

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Best Practices

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Single Root Component

Use StartClient once at your application root: 
// ✅ Good
hydrateRoot(document.getElementById('root')!, <StartClient />)

// ❌ Bad - don't nest StartClient
function App() {
  return <StartClient /> // Already rendered at root
}

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Server vs Client Imports

Use the correct import for each environment: 
// Client entry
import { StartClient } from '@tanstack/react-start'

// Server entry
import { StartServer } from '@tanstack/react-start/server'

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Document Structure

Always render a complete HTML document: 
function RootDocument({ children }: { children: React.ReactNode }) {
  return (
    <html>
      <head>
        <HeadContent />
      </head>
      <body>
        {children}
        <Scripts />
      </body>
    </html>
  )
}

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Hydration Mismatch

Avoid hydration mismatches by ensuring server and client render the same content: 
// ❌ Bad - will cause hydration mismatch
function Component() {
  const [mounted, setMounted] = useState(false)
  useEffect(() => setMounted(true), [])
  return <div>{mounted ? 'Client' : 'Server'}</div>
}

// ✅ Good - consistent across server and client
function Component() {
  return <div>Consistent content</div>
}

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API Reference

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StartClient

Client-side root component. Props: None Example: 
import { StartClient } from '@tanstack/react-start'
hydrateRoot(document.getElementById('root')!, <StartClient />)

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StartServer

Server-side root component. Props:
  • router: AnyRouter - Router instance
Example: 
import { StartServer } from '@tanstack/react-start/server'
<StartServer router={router} />

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hydrateStart

Hydrates the router on the client. Returns: Promise<AnyRouter> Example: 
import { hydrateStart } from '@tanstack/react-start/client'
const router = await hydrateStart()

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