[raon0211]

Overview

Adds flow to es-toolkit/fp — the deferred sibling of pipe. Where pipe(value, ...fns) threads a concrete value through the functions immediately, flow(...fns) returns a reusable function you can call later with different data.

The first function may take any number of arguments; every later function is unary and receives the previous result (same shape as the main es-toolkit flow).

Implementation note: built on pipe

flow does not reimplement composition — it delegates to pipe so lazy-capable operators (map, filter, take, …) are fused and short-circuit exactly as they do in pipe:

• Single argument (fn(x)): runs pipe(x, ...functions), so a leading lazy operator stays inside the fused run instead of being applied eagerly.
• Multiple arguments (fn(x, y, …)): only the first function may be variadic, so it is invoked directly (first(...args)) and the rest go through pipe.

Overloads cover up to 15 functions, matching pipe.

Changes

• src/fp/flow.ts — implementation + JSDoc, 15 overloads, runtime delegates to pipe.
• src/fp/index.ts, src/fp/index.spec.ts — public export + export test.
• src/fp/flow.spec.ts — runtime tests (variadic first fn, unary chain, pipe-parity, lazy short-circuit via spy, reusability) + expectTypeOf checks for first-fn params / final return type.
• Docs in all 4 languages (docs/{,, ko/, ja/, zh_hans/}fp/reference/flow.md), centered on the pipe vs flow difference (immediate vs reusable). Sidebar is auto-discovered, no config change needed.

Benchmarks

• benchmarks/performance/fp/flow.bench.ts — es-toolkit/fp vs lodash/fp across scalar composition, flow/map, and a flow/map + filter + take lazy short-circuit case.
• benchmarks/bundle-size/fp/flow.spec.ts — es-toolkit/fp (969 B) vs lodash/fp/flow.

Note: in flow/map (a single eager map over 10k elements, no short-circuit) es-toolkit/fp is slower than lodash/fp — the lazy machinery has fixed overhead that only pays off once an operator can terminate the walk early. The numbers are reported as-is.

Verification

yarn vitest run src/fp/flow.spec.ts src/fp/index.spec.ts   # 12 passed
yarn typecheck                                             # clean
yarn lint                                                  # 0 errors
yarn vitest bench benchmarks/performance/fp/flow.bench.ts --run
yarn vitest run benchmarks/bundle-size/fp/flow.spec.ts     # passed

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview, Comment	Jun 27, 2026 6:34am