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.