es-toolkit/fp

es-toolkit/fp is the functional-programming entry point for es-toolkit. It lets you express a data transformation as a readable, top-to-bottom pipeline with pipe, instead of nesting calls or juggling temporary variables.

import { filter, map, pipe, take } from 'es-toolkit/fp';

const result = pipe(
  [1, 2, 3, 4, 5, 6],
  filter(x => x % 2 === 0),
  map(x => x * 10),
  take(2)
); // => [20, 40]

How es-toolkit/fp functions work

Every es-toolkit/fp function is called with its configuration (for example map(fn) or take(2)) and returns a function that takes the data. pipe supplies that data, threading the result of each step into the next.

import { map, pipe } from 'es-toolkit/fp';

const triple = map((x: number) => x * 3); // (array) => number[]

pipe([1, 2, 3], triple); // => [3, 6, 9]

Lazy evaluation

When consecutive lazy-capable functions (map, filter, take, …) appear together, pipe fuses them into a single pass over the data and processes one element at a time. A trailing take can then end the walk early, so the earlier functions never run on the rest of the input.

import { filter, map, pipe, take } from 'es-toolkit/fp';

pipe(
  hugeArray,
  map(expensiveTransform),
  filter(complexPredicate),
  // Stops as soon as 2 results are collected; most of `hugeArray` is never visited.
  take(2)
);

Relationship to es-toolkit

es-toolkit/fp reuses the implementations from es-toolkit; it only changes how you call them — inside pipe. If you prefer direct calls, use es-toolkit. To match Lodash call sites while migrating, use es-toolkit/compat.