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/flatMap.md.
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    flatMap (Functional Programming) es-toolkit

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

    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.

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

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

    Parameters

    callback(value: T, index: number) => U[]required

    The function that maps each value to an array.

    Returns

    A function that maps a readonly T[] to a flattened array of callback results.

    (array: readonly T[]) => 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.