Client Data

You can fetch and mutate data directly in the browser using clientLoader and clientAction functions.

These functions are the primary mechanism for data handling when using SPA mode. This guide demonstrates common use cases for leveraging client data in Server-Side Rendering (SSR).

Skip the Server Hop

When using React Router with a Backend-For-Frontend (BFF) architecture, you might want to bypass the React Router server and communicate directly with your backend API. This approach requires proper authentication handling and assumes no CORS restrictions. Here's how to implement this:

Load the data from server loader on the document load
Load the data from the clientLoader on all subsequent loads

In this scenario, React Router will not call the clientLoader on hydration - and will only call it on subsequent navigations.

export async function loader({
  request,
}: Route.LoaderArgs) {
  const data = await fetchApiFromServer({ request }); // (1)
  return data;
}

export async function clientLoader({
  request,
}: Route.ClientLoaderArgs) {
  const data = await fetchApiFromClient({ request }); // (2)
  return data;
}

Fullstack State

Sometimes you need to combine data from both the server and browser (like IndexedDB or browser SDKs) before rendering a component. Here's how to implement this pattern:

Load the partial data from server loader on the document load
Export a HydrateFallback component to render during SSR because we don't yet have a full set of data
Set clientLoader.hydrate = true, this instructs React Router to call the clientLoader as part of initial document hydration
Combine the server data with the client data in clientLoader

export async function loader({
  request,
}: Route.LoaderArgs) {
  const partialData = await getPartialDataFromDb({
    request,
  }); // (1)
  return partialData;
}

export async function clientLoader({
  request,
  serverLoader,
}: Route.ClientLoaderArgs) {
  const [serverData, clientData] = await Promise.all([
    serverLoader(),
    getClientData(request),
  ]);
  return {
    ...serverData, // (4)
    ...clientData, // (4)
  };
}
clientLoader.hydrate = true as const; // (3)

export function HydrateFallback() {
  return <p>Skeleton rendered during SSR</p>; // (2)
}

export default function Component({
  // This will always be the combined set of server + client data
  loaderData,
}: Route.ComponentProps) {
  return <>...</>;
}

Choosing Server or Client Data Loading

You can mix data loading strategies across your application, choosing between server-only or client-only data loading for each route. Here's how to implement both approaches:

Export a loader when you want to use server data
Export clientLoader and a HydrateFallback when you want to use client data

A route that only depends on a server loader looks like this:

export async function loader({
  request,
}: Route.LoaderArgs) {
  const data = await getServerData(request);
  return data;
}

export default function Component({
  loaderData, // (1) - server data
}: Route.ComponentProps) {
  return <>...</>;
}

A route that only depends on a client loader looks like this.

export async function clientLoader({
  request,
}: Route.ClientLoaderArgs) {
  const clientData = await getClientData(request);
  return clientData;
}
// Note: you do not have to set this explicitly - it is implied if there is no `loader`
clientLoader.hydrate = true;

// (2)
export function HydrateFallback() {
  return <p>Skeleton rendered during SSR</p>;
}

export default function Component({
  loaderData, // (2) - client data
}: Route.ComponentProps) {
  return <>...</>;
}

Client-Side Caching

You can implement client-side caching (using memory, localStorage, etc.) to optimize server requests. Here's a pattern that demonstrates cache management:

Load the data from server loader on the document load
Set clientLoader.hydrate = true to prime the cache
Load subsequent navigations from the cache via clientLoader
Invalidate the cache in your clientAction

Note that since we are not exporting a HydrateFallback component, we will SSR the route component and then run the clientLoader on hydration, so it's important that your loader and clientLoader return the same data on initial load to avoid hydration errors.

export async function loader({
  request,
}: Route.LoaderArgs) {
  const data = await getDataFromDb({ request }); // (1)
  return data;
}

export async function action({
  request,
}: Route.ActionArgs) {
  await saveDataToDb({ request });
  return { ok: true };
}

let isInitialRequest = true;

export async function clientLoader({
  request,
  serverLoader,
}: Route.ClientLoaderArgs) {
  const cacheKey = generateKey(request);

  if (isInitialRequest) {
    isInitialRequest = false;
    const serverData = await serverLoader();
    cache.set(cacheKey, serverData); // (2)
    return serverData;
  }

  const cachedData = await cache.get(cacheKey);
  if (cachedData) {
    return cachedData; // (3)
  }

  const serverData = await serverLoader();
  cache.set(cacheKey, serverData);
  return serverData;
}
clientLoader.hydrate = true; // (2)

export async function clientAction({
  request,
  serverAction,
}: Route.ClientActionArgs) {
  const cacheKey = generateKey(request);
  cache.delete(cacheKey); // (4)
  const serverData = await serverAction();
  return serverData;
}