[raon0211]

Closes #1658

Summary

Adds flowAsync to es-toolkit/fp: left-to-right function composition that returns a reusable async function, awaiting every intermediate result.

import { flowAsync } from 'es-toolkit/fp';

const fetchUser = async (id: number) => ({ id, name: 'Alice' });
const getName = (user: { name: string }) => user.name;

const getUserName = flowAsync(fetchUser, getName);
await getUserName(1); // => 'Alice'

Where flow passes each raw return value straight to the next function (so a returned Promise arrives unresolved), flowAsync awaits every step, letting synchronous and asynchronous functions mix freely in one chain. This follows the existing attempt/attemptAsync naming convention.

Implementation notes

• Runtime is the simple loop proposed in the issue: apply the first (possibly variadic) function with all arguments, then await each result before passing it on. The composed function always returns a Promise.
• 15 typed overloads mirror flow, with each step receiving Awaited<R> of the previous result and the final return typed as Promise<Awaited<R>>, so sync/async chains infer precisely.
• Unlike flow, it does not delegate to pipe: awaiting between steps rules out lazy-operator fusion, so each step runs eagerly. fp operators (map, filter, take, …) still compose correctly (covered by tests).
• No performance benchmark: lodash/fp has no flowAsync to compare against, matching the existing convention of not benchmarking async functions. Bundle-size snapshot added (194 bytes).

Checklist

• Implementation: src/fp/flowAsync.ts
• Tests: src/fp/flowAsync.spec.ts (promise resolution, sync/async mixing, ordering, error propagation, reuse, type inference)
• Exported from src/fp/index.ts
• Docs in en/ko/ja/zh_hans: docs/**/fp/reference/flowAsync.md
• Bundle-size benchmark: benchmarks/bundle-size/fp/flowAsync.spec.ts
• yarn vitest run src (687 files, 4803 tests passed), tsc --noEmit, yarn lint, prettier

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview	Aug 22, 2026 8:43am