map (Functional Programming)

Creates a function that transforms every element of an array, equivalent to Array.prototype.map. Use it with pipe.

const result = pipe(array, map(callbackfn));

::: info

This helper is specific to es-toolkit/fp. Use it when you want this operation as part of a pipe pipeline.

:::

Usage

map builds a new array by calling callbackfn on each element. It is lazy-capable: inside a pipe it is fused with adjacent lazy operations, so a trailing take can stop the work early.

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

// Transform each element.
pipe(
  [1, 2, 3],
  map(x => x * 2)
); // => [2, 4, 6]

// The index is available as the second argument.
pipe(
  [10, 20, 30],
  map((value, index) => value + index)
); // => [10, 21, 32]

// The element type can change.
pipe(
  [1, 2, 3],
  map(x => `#${x}`)
); // => ['#1', '#2', '#3']

Parameters

• callbackfn ((value: T, index: number) => U): A function called for each element; its return value becomes the corresponding element of the output array.

Returns

((array: readonly T[]) => U[]): A function that maps a readonly T[] to a new U[].