Optimizes async JavaScript with rules for Promise.all parallelism, deferring awaits, dependency chaining, early loader promises, and Suspense boundaries to eliminate waterfalls in data fetching and actions.
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Performance optimization patterns for asynchronous JavaScript code. Contains 5 rules focused on eliminating request waterfalls and maximizing parallelism.
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Performance optimization patterns for asynchronous JavaScript code. Contains 5 rules focused on eliminating request waterfalls and maximizing parallelism.
Impact: CRITICAL - Waterfalls are the #1 performance killer. Each sequential await adds full network latency.
Reference these guidelines when:
Use Promise.all() for independent operations.
// Bad: 3 sequential round trips
const user = await fetchUser();
const posts = await fetchPosts();
const comments = await fetchComments();
// Good: 1 parallel round trip
const [user, posts, comments] = await Promise.all([
fetchUser(),
fetchPosts(),
fetchComments(),
]);
Move await into branches where actually used.
// Bad: always waits even when skipping
async function handle(skip: boolean) {
let data = await fetchData();
if (skip) return { skipped: true };
return process(data);
}
// Good: only waits when needed
async function handle(skip: boolean) {
if (skip) return { skipped: true };
let data = await fetchData();
return process(data);
}
Chain dependent operations, parallelize independent ones.
// Bad: profile waits for config unnecessarily
const [user, config] = await Promise.all([fetchUser(), fetchConfig()]);
const profile = await fetchProfile(user.id);
// Good: profile starts as soon as user resolves
const userPromise = fetchUser();
const profilePromise = userPromise.then((user) => fetchProfile(user.id));
const [user, config, profile] = await Promise.all([
userPromise,
fetchConfig(),
profilePromise,
]);
Start promises early, await late in loaders.
// Bad: sequential execution
export async function loader() {
let session = await auth();
let config = await fetchConfig();
return { session, config };
}
// Good: parallel execution
export async function loader() {
let sessionPromise = auth();
let configPromise = fetchConfig();
const [session, config] = await Promise.all([sessionPromise, configPromise]);
return { session, config };
}
Use Suspense to show UI immediately while data loads.
// Bad: entire page blocked by data
async function Page() {
let data = await fetchData();
return (
<Layout>
<Content data={data} />
</Layout>
);
}
// Good: layout shows immediately, content streams in
function Page() {
return (
<Layout>
<Suspense fallback={<Skeleton />}>
<Content />
</Suspense>
</Layout>
);
}