React Router 7 Framework Mode Best Practices

Version Compatibility

This skill targets React Router 7.9.0+ in framework mode. Key features by version:

Future Flags

Enable v8 features in react-router.config.ts:

import type { Config } from "@react-router/dev/config";

export default {
  future: {
    v8_middleware: true,        // Middleware support
    v8_splitRouteModules: true, // Route module splitting for performance
  },
} satisfies Config;

These will become the default in v8.

Core Principles

1. Server-First: Fetch and process data on the server whenever possible. Only use client-side data fetching when absolutely necessary.
2. Maximum Type Safety: Always use React Router 7’s generated types (Route.LoaderArgs, Route.ComponentProps, etc.). Access loader/action data from props or use typeof loader/typeof action with hooks.
3. Proper Hydration: Understand when to use clientLoader.hydrate = true and when to skip it
4. Declarative Data: Colocate data requirements with routes using loaders
5. Progressive Enhancement: Use actions for mutations with automatic revalidation

Route Configuration

Define routes in app/routes.ts using helper functions:

import type { RouteConfig } from "@react-router/dev/routes";
import { route, index, layout, prefix } from "@react-router/dev/routes";

export default [
  index("./home.tsx"),
  route("about", "./about.tsx"),
  layout("./auth-layout.tsx", [
    route("login", "./login.tsx"),
    route("register", "./register.tsx"),
  ]),
  ...prefix("api", [
    route("users", "./api/users.tsx"),
  ]),
  route("*", "./not-found.tsx"), // Catch-all 404
] satisfies RouteConfig;

See references/routes-config.md for layout routes, Outlet, splat routes, custom IDs, and nested route patterns.

Type Safety

Generated Types

React Router 7 generates route-specific types in .react-router/types/+types/<route-file>.d.ts for each route. Always import and use these types:

import type { Route } from "./+types/product";

export async function loader({ params }: Route.LoaderArgs) {
  // params is typed based on your route definition
  const product = await db.getProduct(params.id);
  return { product };
}

export default function Product({ loaderData }: Route.ComponentProps) {
  // loaderData is inferred from loader return type
  return <h1>{loaderData.product.name}</h1>;
}

Available Route Types

• Route.LoaderArgs – Types for loader parameters (params, request, context)
• Route.ActionArgs – Types for action parameters
• Route.ClientLoaderArgs – Types for clientLoader parameters (includes serverLoader)
• Route.ClientActionArgs – Types for clientAction parameters (includes serverAction)
• Route.ComponentProps – Types for component props (includes loaderData, actionData, matches, etc.)

Accessing Loader/Action Data

In route module default exports, always use props — they provide the best type safety and are the recommended approach in framework mode:

import type { Route } from "./+types/product";

export async function loader() {
  return { product: await db.getProduct() };
}

export async function action() {
  return { success: true };
}

// ✅ Props are auto-typed for this specific route
export default function Product({
  loaderData,
  actionData,
}: Route.ComponentProps) {
  return <div>{loaderData.product.name}</div>;
}

When to use hooks instead:

Hooks (useLoaderData, useActionData) are for non-route-module contexts — deep child components, shared UI, or when testing:

// In a child component that doesn't have direct access to route props
import { useLoaderData } from "react-router";

function ProductDetails() {
  // Use typeof for type inference
  const { product } = useLoaderData<typeof import("./route").loader>();
  return <span>{product.description}</span>;
}

Note: Hook generics like useLoaderData<typeof loader>() exist largely for migration from Remix and are considered secondary to the props pattern. The Route.* types via props are the “most type-safe / least foot-gun” approach.

❌ Never use: useLoaderData<Route.ComponentProps["loaderData"]>() — this pattern is incorrect.

Type-Safe Links

Use the href utility for type-safe route generation (v7.5+):

import { href } from "react-router";
import { Link, NavLink } from "react-router";

// Basic usage with params
<Link to={href("/products/:id", { id: "123" })} />

// Optional params
<NavLink to={href("/:lang?/about", { lang: "en" })} />

// No params needed
<Link to={href("/contact")} />

// Programmatic use
const productLink = href("/products/:id", { id: productId });
navigate(productLink);

// Type errors caught at compile time:
href("/not/a/valid/path");         // ❌ Error: Invalid path
href("/blog/:slug", { oops: 1 });  // ❌ Error: Invalid param name
href("/blog/:slug", {});           // ❌ Error: Missing required param

Benefits:

• Compile-time validation of route paths
• Required params are enforced
• Refactoring routes updates all usages
• IDE autocomplete for available routes

Data Loading Patterns

1. Server-Only Loading (Preferred)

Default pattern – load data on the server, hydrate automatically:

import type { Route } from "./+types/products";

export async function loader({ params, request }: Route.LoaderArgs) {
  // Runs on server during SSR and on server during client navigations
  const product = await db.getProduct(params.id);
  return { product };
}

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.product.name}</div>;
}

When to use: This is the default and preferred pattern. Use unless you have specific client-side requirements.

2. Client-Only Loading

Load data exclusively on the client:

import type { Route } from "./+types/products";

export async function clientLoader({ params }: Route.ClientLoaderArgs) {
  // Only runs in the browser
  const res = await fetch(`/api/products/${params.id}`);
  return await res.json();
}

// Required when clientLoader runs during hydration
export function HydrateFallback() {
  return <div>Loading...</div>;
}

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.name}</div>;
}

When to use:

• Accessing browser-only APIs (localStorage, IndexedDB)
• Client-side caching strategies
• No server environment available

Important: clientLoader.hydrate = true is implicit when no server loader exists.

3. Combined Server + Client Loading

Augment server data with client data:

import type { Route } from "./+types/products";

export async function loader({ params }: Route.LoaderArgs) {
  // Server data (e.g., from database)
  return await db.getProduct(params.id);
}

export async function clientLoader({
  params,
  serverLoader,
}: Route.ClientLoaderArgs) {
  // Get server data + add client data
  const [serverData, clientData] = await Promise.all([
    serverLoader(),
    getClientOnlyData(params.id),
  ]);
  return { ...serverData, ...clientData };
}
clientLoader.hydrate = true as const; // Use 'as const' for proper type inference

export function HydrateFallback() {
  return <div>Loading...</div>;
}

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.name}</div>;
}

When to use:

• Combining server data with client-only data (user preferences, client state)
• Augmenting server data with cached data

Important: Set clientLoader.hydrate = true as const to call clientLoader during initial hydration.

4. Skip Server Hop (BFF Pattern)

Load server data on initial request, then call client API directly:

import type { Route } from "./+types/products";

export async function loader({ params }: Route.LoaderArgs) {
  // Server loads data on initial document request
  const product = await db.getProduct(params.id);
  return { product };
}

export async function clientLoader({ params }: Route.ClientLoaderArgs) {
  // Subsequent navigations fetch from API directly (skip server hop)
  const res = await fetch(`/api/products/${params.id}`);
  return await res.json();
}
// clientLoader.hydrate is false (default) - only runs on subsequent navigations

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.product.name}</div>;
}

When to use:

• Backend-For-Frontend pattern
• Initial SSR data load, then direct API calls
• Authentication/cookies work for both server and client

Important: Do NOT set clientLoader.hydrate = true for this pattern. You want clientLoader to skip during hydration.

5. Client-Side Caching

Cache server data on client for subsequent navigations:

import type { Route } from "./+types/products";

let isInitialRequest = true;
const cache = new Map();

export async function loader({ params }: Route.LoaderArgs) {
  return await db.getProduct(params.id);
}

export async function clientLoader({
  params,
  serverLoader,
}: Route.ClientLoaderArgs) {
  const cacheKey = `product-${params.id}`;

  // First request: prime cache
  if (isInitialRequest) {
    isInitialRequest = false;
    const data = await serverLoader();
    cache.set(cacheKey, data);
    return data;
  }

  // Subsequent requests: use cache
  const cached = cache.get(cacheKey);
  if (cached) return cached;

  const data = await serverLoader();
  cache.set(cacheKey, data);
  return data;
}
clientLoader.hydrate = true as const;

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.name}</div>;
}

When to use:

• Optimizing for repeated visits to same routes
• Reducing server round-trips
• Offline-first strategies

Actions and Mutations

Server Actions (Preferred)

Handle mutations on the server with automatic revalidation:

import type { Route } from "./+types/todos";
import { Form } from "react-router";

export async function loader() {
  // This runs after action completes
  const todos = await db.getTodos();
  return { todos };
}

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const title = formData.get("title");
  await db.createTodo({ title });
  return { success: true };
}

export default function Todos({ loaderData }: Route.ComponentProps) {
  return (
    <div>
      <ul>
        {loaderData.todos.map((todo) => (
          <li key={todo.id}>{todo.title}</li>
        ))}
      </ul>
      <Form method="post">
        <input type="text" name="title" />
        <button type="submit">Add Todo</button>
      </Form>
    </div>
  );
}

Key features:

• Automatic revalidation of all loaders after action completes
• Type-safe with Route.ActionArgs
• Works with <Form>, useFetcher, and useSubmit

Client Actions

Handle mutations in the browser, optionally calling server action:

import type { Route } from "./+types/todos";

export async function action({ request }: Route.ActionArgs) {
  // Server mutation
  const formData = await request.formData();
  await db.createTodo({ title: formData.get("title") });
  return { success: true };
}

export async function clientAction({
  request,
  serverAction,
}: Route.ClientActionArgs) {
  // Invalidate client cache first
  clientCache.invalidate();

  // Optionally call server action
  const result = await serverAction();
  return result;
}

export default function Todos({ loaderData }: Route.ComponentProps) {
  return <Form method="post">{/* form fields */}</Form>;
}

When to use:

• Need to invalidate client caches before server mutation
• Optimistic UI updates
• Client-side validation before server call

The data() Utility

Use data() to return responses with custom status codes and headers from loaders and actions:

import { data } from "react-router";
import type { Route } from "./+types/item";

// Return with custom status and headers
export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const item = await createItem(formData);

  return data(item, {
    status: 201,
    headers: { "X-Custom-Header": "value" },
  });
}

// Throw 404 to trigger ErrorBoundary
export async function loader({ params }: Route.LoaderArgs) {
  const project = await db.getProject(params.id);

  if (!project) {
    throw data(null, { status: 404 });
  }

  return { project };
}

Common status codes:

• 201 – Resource created (after successful POST)
• 400 – Bad request (validation errors)
• 404 – Not found (missing resource)
• 403 – Forbidden (unauthorized access)

Thrown vs returned:

• throw data(...) – Triggers ErrorBoundary, stops execution
• return data(...) – Returns response, continues rendering

Route Module Exports

Beyond loader, action, and the default component, route modules can export additional functions for metadata, headers, and revalidation control.

meta

Export page metadata (title, description, og tags):

import type { Route } from "./+types/product";

export function meta({ data }: Route.MetaArgs) {
  return [
    { title: data.product.name },
    { name: "description", content: data.product.description },
    { property: "og:title", content: data.product.name },
  ];
}

links

Export link tags (stylesheets, preloads, favicons):

import type { Route } from "./+types/product";

export function links() {
  return [
    { rel: "stylesheet", href: "/styles/product.css" },
    { rel: "preload", href: "/fonts/brand.woff2", as: "font", type: "font/woff2" },
  ];
}

headers

Control HTTP response headers:

import type { Route } from "./+types/product";

export function headers({ loaderHeaders }: Route.HeadersArgs) {
  return {
    "Cache-Control": loaderHeaders.get("Cache-Control") ?? "max-age=300",
    "X-Custom-Header": "value",
  };
}

shouldRevalidate

Control when loaders re-run (optimize performance):

import type { Route } from "./+types/products";

export function shouldRevalidate({
  currentUrl,
  nextUrl,
  defaultShouldRevalidate,
}: Route.ShouldRevalidateArgs) {
  // Don't revalidate if only search params changed
  if (currentUrl.pathname === nextUrl.pathname) {
    return false;
  }

  return defaultShouldRevalidate;
}

Use cases for shouldRevalidate:

• Skip revalidation when navigating within the same route
• Prevent unnecessary refetches after certain actions
• Optimize performance for expensive loaders

ErrorBoundary

Handle errors that occur during loading or rendering:

import { isRouteErrorResponse, useRouteError } from "react-router";

export function ErrorBoundary() {
  const error = useRouteError();

  if (isRouteErrorResponse(error)) {
    return (
      <div>
        <h1>{error.status} {error.statusText}</h1>
        <p>{error.data}</p>
      </div>
    );
  }

  return <div>Something went wrong</div>;
}

Server-Only Modules

Use .server and .client module conventions to prevent accidentally bundling server-only code (secrets, database clients) into the client bundle.

.server Modules

Files ending in .server.ts or in a .server/ directory are never bundled into the client:

app/
├── utils/
│   ├── db.server.ts      # Server-only: database client
│   ├── auth.server.ts    # Server-only: auth logic with secrets
│   └── format.ts         # Shared: safe for client and server
└── .server/
    └── secrets.ts        # Server-only: environment secrets

// app/utils/db.server.ts
import { PrismaClient } from "@prisma/client";

// This code never reaches the client bundle
export const db = new PrismaClient();

// app/routes/products.tsx
import { db } from "~/utils/db.server"; // Safe: only used in loader

export async function loader() {
  const products = await db.product.findMany();
  return { products };
}

.client Modules

Files ending in .client.ts or in a .client/ directory are never bundled into the server:

// app/utils/analytics.client.ts
// Browser-only code (window, document, etc.)
export function trackPageView(path: string) {
  window.gtag?.("event", "page_view", { page_path: path });
}

Why This Matters

• Security: Secrets and credentials stay on the server
• Bundle size: Server-only code doesn’t bloat client bundles
• Compatibility: Browser-incompatible code (Node APIs, database clients) won’t break the client build

Rule of thumb: If a module imports secrets, database clients, or Node-only APIs, name it .server.ts.

Useful Utilities and Hooks

useFetcher

Submit forms and load data without navigation:

import { useFetcher } from "react-router";

function TodoItem({ todo }) {
  const fetcher = useFetcher();
  const isDeleting = fetcher.state === "submitting";

  return (
    <div>
      <span>{todo.title}</span>
      <fetcher.Form method="post" action={`/todos/${todo.id}/delete`}>
        <button disabled={isDeleting}>
          {isDeleting ? "Deleting..." : "Delete"}
        </button>
      </fetcher.Form>
    </div>
  );
}

States: "idle" | "submitting" | "loading" Access data: fetcher.data (from loader/action) Methods: fetcher.submit(), fetcher.load()

useNavigation

Track global navigation state:

import { useNavigation } from "react-router";

function GlobalLoadingIndicator() {
  const navigation = useNavigation();
  const isNavigating = navigation.state !== "idle";

  return isNavigating ? <LoadingSpinner /> : null;
}

States: "idle" | "loading" | "submitting"

useActionData

Access data returned from the most recent action. In route modules, prefer actionData from props (see “Accessing Loader/Action Data” above).

Use useActionData in deep child components:

import { useActionData, Form } from "react-router";

function LoginForm() {
  const actionData = useActionData<typeof import("../route").action>();

  return (
    <Form method="post">
      {actionData?.error && <div>{actionData.error}</div>}
      <input type="email" name="email" />
      <button type="submit">Login</button>
    </Form>
  );
}

Note: actionData is undefined until an action has been called

useLoaderData

Access the current route’s loader data. In route modules, prefer loaderData from props (see “Accessing Loader/Action Data” above).

Use useLoaderData in deep child components that don’t have direct access to route props:

import { useLoaderData } from "react-router";

// In a child component, not the route module default export
function ProductCard() {
  const { products } = useLoaderData<typeof import("../route").loader>();
  return <div>{products[0].name}</div>;
}

Important:

• useLoaderData assumes the loader succeeded
• Cannot be used in ErrorBoundary or Layout components — use useRouteLoaderData for those cases
• Never use useLoaderData<Route.ComponentProps["loaderData"]>() — this is incorrect

useRouteLoaderData

Access loader data from parent or sibling routes by route ID. Essential for ErrorBoundary and Layout components where useLoaderData is not allowed.

Type-safe pattern with typeof:

import { useRouteLoaderData } from "react-router";
import type { loader as rootLoader } from "./root";

export function Layout({ children }) {
  // Type-safe: infers types from root loader
  const rootData = useRouteLoaderData<typeof rootLoader>("root");

  // Always check for undefined (loader may have thrown)
  if (rootData?.user) {
    return <div>Welcome, {rootData.user.name}</div>;
  }

  return <div>Not authenticated</div>;
}

Basic usage (untyped):

import { useRouteLoaderData } from "react-router";

export default function ChildComponent() {
  const rootData = useRouteLoaderData("root");

  if (rootData?.user) {
    return <div>Welcome, {rootData.user.name}</div>;
  }

  return <div>Not authenticated</div>;
}

When to use:

• Accessing parent route data (e.g., user auth from root loader)
• Sharing data across route hierarchy
• In ErrorBoundary or Layout components where useLoaderData is not allowed

Route IDs: Automatically generated from file paths:

• app/root.tsx → "root"
• app/routes/products.tsx → "routes/products"
• app/routes/products.$id.tsx → "routes/products.$id"

You can also specify custom IDs in routes.ts:

import { route } from "@react-router/dev/routes";

export default [
  route("/products/:id", "./product.tsx", { id: "product-detail" }),
];

useMatches

Access all matched routes and their data/handles:

import { useMatches } from "react-router";

export function Layout({ children }) {
  const matches = useMatches();

  // Access all matched routes
  matches.forEach((match) => {
    console.log(match.id);           // Route ID
    console.log(match.pathname);     // URL pathname
    console.log(match.params);       // URL params
    console.log(match.loaderData);   // Loader data (may be undefined)
    console.log(match.handle);       // Custom handle metadata
  });

  return <div>{children}</div>;
}

Note: Use match.loaderData instead of match.data. The data property is deprecated.

Common use cases:

• Building breadcrumbs from route hierarchy
• Creating dynamic navigation based on current route
• Accessing metadata from all matched routes

Type safety with UIMatch:

import { useMatches, type UIMatch } from "react-router";

const matches = useMatches();
const rootMatch = matches[0] as UIMatch<{ user: User } | undefined>;

// Guard against undefined loaderData (loader may have thrown)
if (rootMatch.loaderData?.user) {
  const { user } = rootMatch.loaderData;
}

Form Component

Use React Router’s Form for enhanced form handling:

import { Form } from "react-router";

<Form method="post" action="/todos">
  <input name="title" />
  <button type="submit">Create</button>
</Form>

// With navigate={false} to prevent navigation after action
<Form method="post" navigate={false}>
  {/* ... */}
</Form>

See references/forms.md for form validation patterns, optimistic UI, and pending states.

useParams

Access route parameters in components:

import { useParams } from "react-router";

function ProductDetail() {
  const { productId } = useParams();
  return <div>Product: {productId}</div>;
}

Note: In route modules, prefer accessing params from Route.ComponentProps or Route.LoaderArgs.

useRevalidator

Manually trigger data revalidation:

import { useRevalidator } from "react-router";

function RefreshButton() {
  const revalidator = useRevalidator();

  return (
    <button
      onClick={() => revalidator.revalidate()}
      disabled={revalidator.state === "loading"}
    >
      {revalidator.state === "loading" ? "Refreshing..." : "Refresh"}
    </button>
  );
}

Use cases: Polling, window focus refresh, manual refresh buttons.

useNavigate

Programmatic navigation without user interaction:

import { useNavigate } from "react-router";

function LogoutButton() {
  const navigate = useNavigate();

  const handleLogout = async () => {
    await logout();
    navigate("/login", { replace: true });
  };

  return <button onClick={handleLogout}>Logout</button>;
}

See references/navigation.md for navigation options, Outlet, and redirect patterns.

URL Search Params

For filters, pagination, search, and shareable UI state.

Quick example:

import { useSearchParams } from "react-router";

export default function ProductList() {
  const [searchParams, setSearchParams] = useSearchParams();
  const category = searchParams.get("category") || "all";

  const handleCategoryChange = (newCategory: string) => {
    setSearchParams((prev) => {
      prev.set("category", newCategory);
      prev.set("page", "1"); // Reset page when filter changes
      return prev;
    });
  };

  return (/* ... */);
}

In loaders:

export async function loader({ request }: Route.LoaderArgs) {
  const url = new URL(request.url);
  const category = url.searchParams.get("category") || "all";
  const products = await db.getProducts({ category });
  return { products, category };
}

See references/search-params.md for pagination patterns, filtering with forms, type-safe parsing, and debounced search.

Route Metadata with handle

Export a handle object to attach custom metadata to routes. This metadata is accessible via useMatches() in ancestor components.

Basic handle Export

// app/routes/products.tsx
import { Link } from "react-router";

export const handle = {
  breadcrumb: () => <Link to="/products">Products</Link>,
  title: "Products",
  icon: "📦",
};

Dynamic Breadcrumbs Pattern

Use handle with useMatches to build breadcrumbs:

// app/routes/products.$id.tsx
import type { Route } from "./+types/products.$id";

export async function loader({ params }: Route.LoaderArgs) {
  const product = await db.getProduct(params.id);
  return { product };
}

export const handle = {
  breadcrumb: (match: any) => (
    <Link to={`/products/${match.params.id}`}>
      {match.loaderData?.product?.name || "Product"}
    </Link>
  ),
};

export default function Product({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.product.name}</div>;
}

Rendering Breadcrumbs in Layout

// app/root.tsx
import { useMatches, Outlet } from "react-router";

export function Layout({ children }) {
  const matches = useMatches();

  return (
    <html>
      <body>
        <nav>
          <ol>
            {matches
              .filter((match) => match.handle?.breadcrumb)
              .map((match, index) => (
                <li key={index}>
                  {match.handle.breadcrumb(match)}
                </li>
              ))}
          </ol>
        </nav>
        {children}
      </body>
    </html>
  );
}

export default function App() {
  return <Outlet />;
}

Common handle use cases:

• Breadcrumb navigation
• Page titles and metadata
• Icons for navigation items
• Role-based access control metadata
• Analytics tracking data

Middleware (v7.9.0+)

Middleware runs code before/after route handlers for authentication, logging, context sharing.

Quick example:

// app/middleware/auth.ts
import { redirect, createContext } from "react-router";

export const userContext = createContext<User>();

export async function authMiddleware({ request, context }) {
  const session = await getSession(request);
  if (!session.get("userId")) throw redirect("/login");

  const user = await getUserById(session.get("userId"));
  context.set(userContext, user);
}

// app/routes/dashboard.tsx
export const middleware = [authMiddleware] satisfies Route.MiddlewareFunction[];

export async function loader({ context }: Route.LoaderArgs) {
  const user = context.get(userContext);
  return { user };
}

Enable with future.v8_middleware: true in react-router.config.ts.

See references/middleware.md for execution order, error handling, and role-based access patterns.

SSR and Pre-rendering

Configure SSR

Enable server-side rendering in react-router.config.ts:

import type { Config } from "@react-router/dev/config";

export default {
  ssr: true,
} satisfies Config;

Configure Pre-rendering

Generate static HTML at build time:

import type { Config } from "@react-router/dev/config";

export default {
  ssr: true, // Can be true or false
  async prerender() {
    return ["/", "/about", "/products", "/contact"];
  },
} satisfies Config;

Static-only mode (no runtime server):

export default {
  ssr: false,
  prerender: true, // Pre-renders all static routes
} satisfies Config;

Async Streaming with Promises

Stream non-critical data while rendering critical data immediately. defer() is deprecated – just return promises directly.

Quick example:

export async function loader() {
  const user = await db.getUser(); // Critical - await
  const stats = db.getStats();     // Non-critical - don't await

  return { user, stats };
}

export default function Dashboard({ loaderData }: Route.ComponentProps) {
  const { user, stats } = loaderData;

  return (
    <div>
      <h1>Welcome, {user.name}!</h1>
      <Suspense fallback={<StatsSkeleton />}>
        <Await resolve={stats}>
          {(resolvedStats) => <StatsCard data={resolvedStats} />}
        </Await>
      </Suspense>
    </div>
  );
}

Important: Promises must be wrapped in an object (return { reviews } not return reviews).

See references/streaming.md for error handling, useAsyncValue patterns, and when to use streaming.

Common Patterns

Loading States with HydrateFallback

Show loading UI during initial hydration when clientLoader.hydrate = true:

export async function clientLoader({ serverLoader }: Route.ClientLoaderArgs) {
  const data = await serverLoader();
  return data;
}
clientLoader.hydrate = true as const;

export function HydrateFallback() {
  return <div>Loading...</div>;
}

export default function Component({ loaderData }: Route.ComponentProps) {
  return <div>{loaderData.content}</div>;
}

Important: HydrateFallback cannot render <Outlet /> as child routes may not be ready.

Error Handling

Use error boundaries for loader/action errors:

import { isRouteErrorResponse, useRouteError } from "react-router";

export function ErrorBoundary() {
  const error = useRouteError();

  if (isRouteErrorResponse(error)) {
    return (
      <div>
        <h1>{error.status} {error.statusText}</h1>
        <p>{error.data}</p>
      </div>
    );
  }

  return <div>Something went wrong!</div>;
}

Pending UI with useNavigation

Show pending states during navigation:

import { useNavigation } from "react-router";

export default function Products({ loaderData }: Route.ComponentProps) {
  const navigation = useNavigation();
  const isLoading = navigation.state === "loading";

  return (
    <div className={isLoading ? "opacity-50" : ""}>
      {loaderData.products.map((product) => (
        <ProductCard key={product.id} product={product} />
      ))}
    </div>
  );
}

Resource Routes (API Endpoints)

Resource routes serve non-UI responses (JSON, PDF, webhooks). A route is a resource route when it exports loader/action but no default component:

// app/routes/api.users.tsx
export async function loader() {
  const users = await db.getUsers();
  return Response.json(users);
}

export async function action({ request }: Route.ActionArgs) {
  const data = await request.json();
  const user = await db.createUser(data);
  return Response.json(user, { status: 201 });
}
// No default export = resource route

Link with reloadDocument to prevent client-side routing:

<Link reloadDocument to="/api/report.pdf">Download PDF</Link>

See references/resource-routes.md for HTTP method handling, file serving, and webhook patterns.

Decision Tree

Do you need to access client-only APIs (localStorage, browser state)?
├─ YES → Use clientLoader (no server loader)
└─ NO  → Continue

Do you need to combine server and client data?
├─ YES → Use loader + clientLoader with hydrate = true
└─ NO  → Continue

Do you want to cache data on the client?
├─ YES → Use loader + clientLoader with caching logic + hydrate = true
└─ NO  → Continue

Do you want to skip server on subsequent navigations?
├─ YES → Use loader + clientLoader (BFF pattern, no hydrate)
└─ NO  → Continue

Do you have slow/non-critical data that blocks rendering?
├─ YES → Return promises without awaiting - wrap with Suspense/Await in component
└─ NO  → Use server-only loader (PREFERRED)

Checklist

Before completing any React Router 7 implementation:

• All route modules use Route.* types from ./+types/<route>
• Data fetching prioritizes server-side loaders
• clientLoader.hydrate = true as const is set correctly when needed
• HydrateFallback is exported when clientLoader.hydrate = true
• Actions use server-side mutations with automatic revalidation
• Forms use <Form> component from react-router, not native <form>
• Type-safe href() utility is used for route generation
• Error boundaries are implemented for route errors
• Loading states use useNavigation or fetcher states
• No client-side data fetching unless absolutely necessary
• Slow/non-critical data returned as promises (not awaited) for streaming
• Critical data is awaited, non-critical data is streamed
• <Await> wrapped in <Suspense> with fallback UI
• Error handling implemented for streaming promises (errorElement or useAsyncError)
• Search params used for shareable UI state (filters, pagination, search)
• Search params validated and parsed in loaders with proper defaults
• Search param values returned from loader and used as defaultValue in forms
• <Form method="get"> used for filter forms (not POST)
• Use useRouteLoaderData instead of useLoaderData in ErrorBoundary/Layout components
• Parent route data accessed via useRouteLoaderData("route-id") with proper undefined checks
• handle exports used for route metadata (breadcrumbs, titles, etc.)
• Middleware used for authentication/authorization instead of loader-only patterns
• Context API (context.set/get) used for sharing data between middleware and loaders
• data() utility used for custom status codes (404, 201, etc.)
• Route IDs understood for useRouteLoaderData calls
• meta, links, headers exports used where appropriate
• shouldRevalidate considered for performance-critical loaders
• Server-only code uses .server.ts naming convention
• Secrets and database clients never imported in client-accessible modules
• Routes configured in routes.ts with appropriate helpers (route, index, layout, prefix)
• Resource routes (API endpoints) export no default component
• Form validation returns errors with data({ errors }, { status: 400 })
• Optimistic UI uses fetcher.formData for immediate feedback

Bundled References

• routes-config.md – Route configuration, helpers, Outlet, splats
• navigation.md – Redirects, useNavigate, Outlet context
• forms.md – Validation, optimistic UI, pending states
• resource-routes.md – API endpoints, webhooks, file serving
• middleware.md – Authentication, context API, execution order
• search-params.md – Pagination, filtering, type-safe parsing
• streaming.md – Suspense, Await, deferred data

External References

• React Router Documentation
• Routing Guide
• Type Safety Guide
• Data Loading
• Actions
• Form Validation
• Resource Routes
• Client Data Patterns
• Streaming & Suspense
• Middleware Guide
• Using handle
• Pending UI

Key Notes

• Always prefer server-side data loading over client-side
• In route modules, use props (Route.ComponentProps) — hooks are for deep child components
• Never use useLoaderData<Route.ComponentProps["loaderData"]>() — this is incorrect
• Use as const when setting clientLoader.hydrate = true
• HydrateFallback is required when clientLoader.hydrate = true
• Return promises without awaiting to stream slow/non-critical data
• Always wrap <Await> in <Suspense> with fallback UI
• useLoaderData cannot be used in ErrorBoundary or Layout — use useRouteLoaderData
• Use .server.ts naming for modules containing secrets or database clients
• Middleware requires future.v8_middleware: true flag (v7.9.0+)