flatMap (Functional Programming)

Creates a function that maps each value to an array and flattens the result by one level. Use it with pipe.

typescript

const result = pipe(array, flatMap(callback));

INFO

Prefer the original es-toolkit flatMap in ordinary code. Use this fp variant when composing transformations with pipe.

Usage

flatMap calls callback for each value in the piped array and concatenates the returned arrays. It is lazy-capable inside pipe.

typescript

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

pipe(
  [1, 2, 3],
  flatMap(value => [value, value * 10])
); // => [1, 10, 2, 20, 3, 30]

callback ((value: T, index: number) => U[]): The function that maps each value to an array.

((array: readonly T[]) => U[]): A function that maps a readonly T[] to a flattened array of callback results.