single-flight

Deduplicate concurrent async calls. While one call with a given key is in flight, all callers share the same underlying promise (single-flight). Optional short-lived (TTL) result cache. Zero dependencies.

Great for collapsing duplicate network requests — e.g. ten components asking for the same user at once should trigger one fetch.

• Zero dependencies, typed, ESM
• Per-key in-flight deduplication + optional cacheMs

Install

npm install @suzukihayate/single-flight

Usage

import { singleFlight } from '@suzukihayate/single-flight';

const getUser = singleFlight(async (id) => {
  const res = await fetch(`/api/users/${id}`);
  return res.json();
});

// These three run a single fetch and all receive the same result:
const [a, b, c] = await Promise.all([getUser(1), getUser(1), getUser(1)]);

// Optionally cache resolved values for a short window:
const search = singleFlight(doSearch, { cacheMs: 2000 });

// Custom key:
const load = singleFlight(loader, { key: (opts) => opts.id });

API

• singleFlight(fn, { key?, cacheMs? }) → wrapped function
  • key(...args) — derive the dedup key (default JSON.stringify(args))
  • cacheMs — also cache resolved values for this many ms (default 0)
• Wrapped function extras:
  • .clear(key?) — drop in-flight + cached entries (one key, or all)
  • .inflight — number of in-flight keys

Rejections are not cached, and the in-flight slot is released so the next call retries.

Test

node --test

License

MIT © 2026 Hayate Suzuki