flattenDeep (Lodash Compatibility)

::: warning Use flattenDeep from es-toolkit

This flattenDeep function operates slowly due to handling null or undefined, ArrayLike type processing, and supporting various condition function formats.

Use the faster and more modern flattenDeep from es-toolkit instead.

:::

Completely flattens an array.

const result = flattenDeep(array);

Usage

flattenDeep(value)

Recursively flattens a nested array at all depths. All nesting levels are removed, returning a completely flattened one-dimensional array.

import { flattenDeep } from 'es-toolkit/compat';

// Completely flatten a deeply nested array
flattenDeep([1, [2, [3, [4]], 5]]);
// Result: [1, 2, 3, 4, 5]

// Completely flatten a complex nested structure
flattenDeep([1, [2, [3, [[[[4]]]]], 5]]);
// Result: [1, 2, 3, 4, 5]

// Support for mixed types
flattenDeep(['a', ['b', ['c', [['d']]]]]);
// Result: ['a', 'b', 'c', 'd']

Empty arrays, null, or undefined return empty arrays.

import { flattenDeep } from 'es-toolkit/compat';

flattenDeep(null); // []
flattenDeep(undefined); // []
flattenDeep([]); // []

Already flattened arrays are copied as-is.

import { flattenDeep } from 'es-toolkit/compat';

flattenDeep([1, 2, 3, 4, 5]);
// Result: [1, 2, 3, 4, 5]

Parameters

• value (ListOfRecursiveArraysOrValues<T> | null | undefined): The array to completely flatten.

Returns

(Array<T>): Returns a new completely flattened array with all nesting removed.