For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/fp/flatMapDeep.md.
Install massaman

    flatMapDeep (Functional Programming) es-toolkit

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

    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.

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

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

    Parameters

    iteratee(item: T, index: number) => Urequired

    The function that maps each value before deep flattening.

    Returns

    A function that maps a readonly T[] to a deeply flattened array.

    (array: readonly T[]) => Array<ExtractNestedArrayType<U>>
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.