React + Remix Patterns

Before writing code

Fetch live docs:

1. Fetch https://remix.run/docs/en/main for Remix documentation
2. Fetch https://react.dev/reference/react for React API reference
3. Web-search site:shopify.dev hydrogen remix patterns for Hydrogen-specific patterns

Why Remix (Not Next.js)

Shopify's Hydrogen is built on Remix:

• Server-first rendering with progressive enhancement
• Loaders and actions for server-side data fetching and mutations
• Nested routes for layout composition
• Built-in form handling without client-side state management
• Streaming SSR for fast perceived performance

Core Remix Concepts

Loaders (Data Fetching)

Server-side function that runs on every GET request:

import { json, type LoaderFunctionArgs } from '@remix-run/node';

export async function loader({ context, params }: LoaderFunctionArgs) {
  const { storefront } = context;
  const { products } = await storefront.query(PRODUCTS_QUERY);
  return json({ products });
}

export default function ProductsPage() {
  const { products } = useLoaderData<typeof loader>();
  return <ProductGrid products={products} />;
}

Actions (Mutations)

Server-side function for form submissions (POST/PUT/DELETE):

import { redirect, type ActionFunctionArgs } from '@remix-run/node';

export async function action({ request, context }: ActionFunctionArgs) {
  const formData = await request.formData();
  const variantId = formData.get('variantId') as string;

  const { cart } = context;
  await cart.addLines([{ merchandiseId: variantId, quantity: 1 }]);

  return redirect('/cart');
}

Nested Routes

Routes compose via <Outlet>:

app/routes/
├── ($locale)._index.tsx                    # Homepage
├── ($locale).products._index.tsx           # Product listing
├── ($locale).products.$handle.tsx          # Product detail
├── ($locale).collections.$handle.tsx       # Collection page
├── ($locale).cart.tsx                       # Cart page
└── ($locale).account.tsx                   # Account layout
    ├── ($locale).account._index.tsx        # Account dashboard
    └── ($locale).account.orders.tsx        # Order history

Error Boundaries

Per-route error handling:

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

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

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

React Hooks

Core Hooks

Remix Hooks

Server vs Client Components

Server Components

• Run only on the server
• Can use async/await directly
• Access databases, APIs, secrets
• No event handlers, no useState, no useEffect
• Default in Remix loaders

Client Components

• Run in the browser
• Use "use client" directive (in React 19+)
• Handle interactivity: clicks, inputs, animations
• Use useState, useEffect, useRef

Form Handling

Remix enhances HTML forms:

import { Form, useNavigation } from '@remix-run/react';

function AddToCartForm({ variantId }: { variantId: string }) {
  const navigation = useNavigation();
  const isAdding = navigation.state === 'submitting';

  return (
    <Form method="post" action="/cart">
      <input type="hidden" name="variantId" value={variantId} />
      <button type="submit" disabled={isAdding}>
        {isAdding ? 'Adding...' : 'Add to Cart'}
      </button>
    </Form>
  );
}

Fetcher (Non-Navigation)

For mutations that shouldn't navigate:

function AddToCartButton({ variantId }: { variantId: string }) {
  const fetcher = useFetcher();
  const isAdding = fetcher.state === 'submitting';

  return (
    <fetcher.Form method="post" action="/cart">
      <input type="hidden" name="variantId" value={variantId} />
      <button disabled={isAdding}>
        {isAdding ? 'Adding...' : 'Add to Cart'}
      </button>
    </fetcher.Form>
  );
}

Streaming SSR

Defer non-critical data for faster initial render:

import { defer } from '@remix-run/node';
import { Await, useLoaderData } from '@remix-run/react';
import { Suspense } from 'react';

export async function loader({ context }: LoaderFunctionArgs) {
  const criticalData = await context.storefront.query(PRODUCT_QUERY);
  const recommendedProducts = context.storefront.query(RECOMMENDATIONS_QUERY);

  return defer({
    product: criticalData.product,
    recommended: recommendedProducts, // not awaited — streams later
  });
}

export default function ProductPage() {
  const { product, recommended } = useLoaderData<typeof loader>();

  return (
    <div>
      <ProductDetail product={product} />
      <Suspense fallback={<Spinner />}>
        <Await resolve={recommended}>
          {(data) => <RecommendedProducts products={data.products} />}
        </Await>
      </Suspense>
    </div>
  );
}

Component Patterns

Composition

function ProductCard({ product, children }: { product: Product; children?: ReactNode }) {
  return (
    <article>
      <ProductImage image={product.featuredImage} />
      <ProductTitle title={product.title} />
      <ProductPrice price={product.priceRange} />
      {children}
    </article>
  );
}

Custom Hooks

function useCart() {
  const fetcher = useFetcher();
  const addToCart = (variantId: string) => {
    fetcher.submit({ variantId }, { method: 'post', action: '/cart' });
  };
  return { addToCart, isAdding: fetcher.state === 'submitting' };
}

Best Practices

• Use loaders for data fetching — never fetch in components with useEffect
• Use actions for mutations — use Remix <Form> over manual fetch
• Use useFetcher for mutations that should not cause navigation
• Use defer() + <Suspense> for non-critical data (recommendations, reviews)
• Implement error boundaries at route level for graceful degradation
• Keep components small and focused — extract custom hooks for reusable logic
• Prefer server rendering — only use client-side state when interactivity requires it
• Avoid useEffect for data fetching — Remix loaders handle this
• Use TypeScript for type safety across loader → component data flow

Fetch the Remix and React documentation for exact API signatures, hook behavior, and streaming patterns before implementing.