The use() hook landed in React 19 and immediately changed how I think about data fetching. Not because it's magic — but because it finally makes Suspense-based data fetching feel like something you'd actually ship to production.
Most articles show you use(promise) inside a toy component and call it a day. This one covers what happens when real users hit your app: race conditions, error boundary placement, streaming with RSC, caching strategies, and the gotchas that will bite you if you're not paying attention.
What use() Actually Is
use() is not a replacement for useEffect. It's a new primitive that lets you read a value from a Promise or Context inside a render function — and it works with Suspense natively.
The mental model: use(promise) suspends the component until the promise resolves, then returns the value. If the promise rejects, the nearest error boundary catches it. If it's still pending, the nearest <Suspense> fallback renders.
// The simplest possible use()
import { use, Suspense } from 'react';
function UserProfile({ userPromise }: { userPromise: Promise<User> }) {
const user = use(userPromise); // suspends until resolved
return <div>{user.name}</div>;
}
export default function Page() {
const promise = fetchUser(42); // create promise OUTSIDE the component
return (
<Suspense fallback={<Skeleton />}>
<UserProfile userPromise={promise} />
</Suspense>
);
}
The critical rule you'll violate once and then never forget: create the promise outside the component, or the component will re-create it on every render and loop forever.
How It Differs from useEffect for Data Fetching
The useEffect pattern you've been writing for years:
function useUser(id: number) {
const [user, setUser] = useState<User | null>(null);
const [loading, setLoading] = useState(true);
const [error, setError] = useState<Error | null>(null);
useEffect(() => {
let cancelled = false;
setLoading(true);
fetchUser(id)
.then(data => { if (!cancelled) setUser(data); })
.catch(err => { if (!cancelled) setError(err); })
.finally(() => { if (!cancelled) setLoading(false); });
return () => { cancelled = true; };
}, [id]);
return { user, loading, error };
}
That's 20 lines managing three state variables, a cleanup flag, and a cancelled ref — before you touch the UI.
With use() and a stable promise:
// api/users.ts
const userCache = new Map<number, Promise<User>>();
export function getUserPromise(id: number): Promise<User> {
if (!userCache.has(id)) {
userCache.set(id, fetchUser(id));
}
return userCache.get(id)!;
}
// components/UserProfile.tsx
import { use } from 'react';
import { getUserPromise } from '@/api/users';
function UserProfile({ id }: { id: number }) {
const user = use(getUserPromise(id));
return (
<div className="profile">
<h2>{user.name}</h2>
<p>{user.email}</p>
</div>
);
}
Loading state lives in Suspense. Error state lives in the error boundary. The component only handles the happy path.
Production Pattern 1: Error Boundaries + Suspense Together
Suspense alone is not enough in production. You need error boundaries co-located with your Suspense wrappers, or a rejected promise will bubble all the way up and crash your layout.
// components/AsyncBoundary.tsx
'use client';
import { Suspense, ReactNode } from 'react';
import { ErrorBoundary } from 'react-error-boundary';
export function AsyncBoundary({
children,
fallback = <DefaultSkeleton />,
errorFallback = <DefaultError />,
}: {
children: ReactNode;
fallback?: ReactNode;
errorFallback?: ReactNode;
}) {
return (
<ErrorBoundary fallback={errorFallback}>
<Suspense fallback={fallback}>
{children}
</Suspense>
</ErrorBoundary>
);
}
Granularity matters. Don't wrap your entire page in one boundary — wrap each independent data section. A failed sidebar API call shouldn't blank out the main content.
Production Pattern 2: Promise Caching to Avoid Race Conditions
The biggest footgun with use(): if your promise is created inside a component that re-renders, you get a new promise on every render. React suspends, re-renders when it resolves, suspends again. Infinite loop.
// lib/promise-cache.ts
class PromiseCache {
private cache = new Map<string, { promise: Promise<unknown>; resolvedAt?: number; ttlMs: number }>();
get<T>(key: string, fetcher: () => Promise<T>, ttlMs = 60_000): Promise<T> {
const entry = this.cache.get(key) as { promise: Promise<T>; resolvedAt?: number; ttlMs: number } | undefined;
if (entry) {
const isExpired = entry.resolvedAt !== undefined && Date.now() - entry.resolvedAt > entry.ttlMs;
if (!isExpired) return entry.promise;
}
const promise = fetcher().then(value => {
const current = this.cache.get(key);
if (current) current.resolvedAt = Date.now();
return value;
});
this.cache.set(key, { promise, ttlMs });
return promise;
}
invalidate(key: string) { this.cache.delete(key); }
}
export const promiseCache = new PromiseCache();
export function getProductPromise(id: string): Promise<Product> {
return promiseCache.get(
`product:${id}`,
() => fetch(`/api/products/${id}`).then(r => r.json()),
5 * 60_000
);
}
Production Pattern 3: Server → Client Promise Passing
With App Router, fetch on the server and pass the promise to a client component:
// app/dashboard/page.tsx (Server Component)
export default async function DashboardPage() {
const statsPromise = getUserData(); // don't await — pass it down
return (
<main>
<Suspense fallback={<StatsSkeleton />}>
<StatsPanel statsPromise={statsPromise} />
</Suspense>
</main>
);
}
// components/StatsPanel.tsx (Client Component)
'use client';
import { use } from 'react';
export function StatsPanel({ statsPromise }: { statsPromise: Promise<UserStats> }) {
const stats = use(statsPromise);
return (
<div className="grid grid-cols-3 gap-4">
<StatCard label="Revenue" value={stats.revenue} />
<StatCard label="Users" value={stats.userCount} />
</div>
);
}
The fetch starts on the server before any client JS runs. No client-side waterfall.
Production Pattern 4: Parallel Data Fetching
Start all promises together — don't chain use() calls sequentially:
export default function UserPage({ params }: { params: { id: string } }) {
const userPromise = getUserPromise(params.id);
const ordersPromise = getOrdersPromise(params.id);
const recsPromise = getRecommendationsPromise(params.id);
return (
<UserView
userPromise={userPromise}
ordersPromise={ordersPromise}
recsPromise={recsPromise}
/>
);
}
Each section renders as its data arrives. Orders can fail without taking down recommendations.
The Gotchas
1. use() can't be called conditionally. Pass a pre-resolved empty promise for the false case:
const EMPTY: Promise<AdminData | null> = Promise.resolve(null);
function Component({ isAdmin, adminPromise }: Props) {
const adminData = use(isAdmin ? adminPromise : EMPTY);
if (!adminData) return null;
return <AdminPanel data={adminData} />;
}
2. Rejected promises are not caught by try/catch. They propagate to the nearest error boundary. Set up your boundaries correctly — don't wrap use() in try/catch.
3. use() does NOT deduplicate identical promises. If two sibling components call use(fetchUser(1)) where fetchUser creates a new promise each time, you get two network requests. The caching layer above is not optional in production.
4. Streaming requires a specific hierarchy. The <Suspense> boundary must be a parent of the use() call — not a sibling or child.
When to Use use() vs TanStack Query
| Scenario | use() |
TanStack Query |
|---|---|---|
| Server → Client promise pass-through | ✅ | ❌ |
| Background refetch / stale-while-revalidate | ❌ | ✅ |
| Optimistic updates | ❌ | ✅ |
| Streaming RSC data | ✅ | ❌ |
| One-shot fetch with Suspense | ✅ | Both |
For complex client-side data with mutations and background sync, TanStack Query is still the right tool. use() shines for the server-to-client data pipeline.
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