v11.3.0 top-level await in ESM build breaks jsdom/vitest (ERR_REQUIRE_ASYNC_MODULE) #397

Summary

lru-cache@11.3.0 (PR #395) introduced a top-level await in the ESM build via src/diagnostics-channel-esm.mts:

export const [metrics, tracing] = await import('node:diagnostics_channel').then(...).catch(...)

This breaks any CJS module that transitively loads the ESM build of lru-cache, most notably jsdom via @asamuzakjp/css-color (which is pure ESM with no CJS entrypoint).

Dependency chain

jsdom (CJS)
  → @asamuzakjp/css-color (pure ESM, "type": "module")
    → lru-cache@11.3.0 (ESM build now has TLA)
      → ERR_REQUIRE_ASYNC_MODULE

Error

Error: require() cannot be used on an ESM graph with top-level await.
Use import() instead. To see where the top-level await comes from,
use --experimental-print-required-tla.
  From jsdom/lib/jsdom/living/css/helpers/css-values.js
  Requiring @asamuzakjp/css-color/dist/esm/index.js

This causes every Vitest test using jsdom to fail — no tests run at all.

Impact

This is affecting projects using Vitest + jsdom on Node 22+. The issue surfaced broadly today via Renovate/Dependabot lock file maintenance PRs that re-resolved lru-cache@^11.x to 11.3.0.

Related jsdom issues filed today:

• jsdom broken on Node 24 due to downstream top-level await jsdom/jsdom#4138 — "jsdom broken on Node 24 due to downstream top-level await"
• [Discussion]: require() cannot be used on an ESM graph with top-level await. Use import() instead. jsdom/jsdom#4137 — "require() cannot be used on an ESM graph with top-level await"

Also related: #396 (Angular test runner memory leak from the same diagnostics-channel feature).

Why this happens

The exports map correctly routes require → CJS and import → ESM. However, when a CJS package (jsdom) requires a pure-ESM package (@asamuzakjp/css-color), Node resolves the ESM graph. Within that ESM graph, lru-cache's ESM entrypoint is loaded — which now contains TLA, making the entire graph impossible to require() synchronously.

Suggested fix

The comment in the source notes: "the first tick of metrics will be missed but that probably doesn't matter much." This suggests a non-blocking approach would be acceptable:

// Instead of TLA:
// export const [metrics, tracing] = await import('node:diagnostics_channel')...

// Use non-blocking init:
let metrics = dummyMetrics, tracing = dummyTracing;
import('node:diagnostics_channel').then(dc => {
  metrics = dc.channel('lru-cache:metrics');
  tracing = dc.tracingChannel('lru-cache:tracing');
}).catch(() => {});
export { metrics, tracing };

This preserves the non-Node fallback behavior without introducing TLA.

Workaround

Pin lru-cache to 11.2.7:

"pnpm": {
  "overrides": {
    "lru-cache": "11.2.7"
  }
}

Versions

• lru-cache: 11.3.0
• jsdom: 29.0.1
• @asamuzakjp/css-color: 5.0.1–5.1.5 (all affected)
• Node: 22+
• Vitest: 4.1.2