flatMapDeep (Functional Programming)

Creates a function that maps each value and deeply flattens the result. Use it with pipe.

typescript

const result = pipe(array, flatMapDeep(iteratee));

::: info

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

:::

Usage

flatMapDeep calls iteratee for each value in the piped array and recursively flattens the returned arrays.

typescript

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

pipe(
  [1, 2],
  flatMapDeep(value => [[value, value]])
); // => [1, 1, 2, 2]

iteratee ((item: T, index: number) => U): The function that maps each value before deep flattening.

((array: readonly T[]) => Array<ExtractNestedArrayType<U>>): A function that maps a readonly T[] to a deeply flattened array.