flatten (Functional Programming)

Creates a function that flattens nested arrays to a given depth. Use it with pipe.

const result = pipe(array, flatten(depth));

::: info

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

:::

Usage

flatten flattens the piped array up to depth. When depth is omitted, it flattens one level. It is lazy-capable for one-level flattening inside pipe.

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

pipe([[1], [2, 3], [4]], flatten()); // => [1, 2, 3, 4]

Parameters

• depth (number, optional): The depth to flatten. Defaults to 1.

Returns

((array: readonly T[]) => Array<FlatArray<T[], D>>): A function that maps a nested array to a flattened array.