Files
stack/packages/mosaic/framework/skills/vercel-react-best-practices/rules/async-suspense-boundaries.md
T
fargo 1a822493ba format: apply repo prettier (3.8.1) to the folded skills tree
963 markdown files reformatted with the repository's pinned prettier so
pnpm format:check covers the folded tree like every other repo file.

The formatter's embedded-language pass also normalized code fences
(TS semicolons, closed HTML tags in examples, lowercased CSS hex colors,
one renumbered list that skipped an index). Alphanumeric token deltas vs
the fold commit were audited file-by-file; all are formatter-equivalent
markup normalizations plus the four sanitized skills.
2026-08-19 14:37:17 -05:00

2.5 KiB

title, impact, impactDescription, tags
title impact impactDescription tags
Strategic Suspense Boundaries HIGH faster initial paint async, suspense, streaming, layout-shift

Strategic Suspense Boundaries

Instead of awaiting data in async components before returning JSX, use Suspense boundaries to show the wrapper UI faster while data loads.

Incorrect (wrapper blocked by data fetching):

async function Page() {
  const data = await fetchData(); // Blocks entire page

  return (
    <div>
      <div>Sidebar</div>
      <div>Header</div>
      <div>
        <DataDisplay data={data} />
      </div>
      <div>Footer</div>
    </div>
  );
}

The entire layout waits for data even though only the middle section needs it.

Correct (wrapper shows immediately, data streams in):

function Page() {
  return (
    <div>
      <div>Sidebar</div>
      <div>Header</div>
      <div>
        <Suspense fallback={<Skeleton />}>
          <DataDisplay />
        </Suspense>
      </div>
      <div>Footer</div>
    </div>
  );
}

async function DataDisplay() {
  const data = await fetchData(); // Only blocks this component
  return <div>{data.content}</div>;
}

Sidebar, Header, and Footer render immediately. Only DataDisplay waits for data.

Alternative (share promise across components):

function Page() {
  // Start fetch immediately, but don't await
  const dataPromise = fetchData();

  return (
    <div>
      <div>Sidebar</div>
      <div>Header</div>
      <Suspense fallback={<Skeleton />}>
        <DataDisplay dataPromise={dataPromise} />
        <DataSummary dataPromise={dataPromise} />
      </Suspense>
      <div>Footer</div>
    </div>
  );
}

function DataDisplay({ dataPromise }: { dataPromise: Promise<Data> }) {
  const data = use(dataPromise); // Unwraps the promise
  return <div>{data.content}</div>;
}

function DataSummary({ dataPromise }: { dataPromise: Promise<Data> }) {
  const data = use(dataPromise); // Reuses the same promise
  return <div>{data.summary}</div>;
}

Both components share the same promise, so only one fetch occurs. Layout renders immediately while both components wait together.

When NOT to use this pattern:

  • Critical data needed for layout decisions (affects positioning)
  • SEO-critical content above the fold
  • Small, fast queries where suspense overhead isn't worth it
  • When you want to avoid layout shift (loading → content jump)

Trade-off: Faster initial paint vs potential layout shift. Choose based on your UX priorities.