flatten (Lodash Compatibility)

Use flatten from es-toolkit

This flatten function operates slowly due to handling null or undefined and ArrayLike type processing.

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

Flattens an array by one level.

const result = flatten(array);

Usage

flatten(array)

Flattens a nested array by one level.

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

// Basic flattening (one level)
flatten([1, [2, [3, [4]], 5]]);
// Result: [1, 2, [3, [4]], 5]

// Support for Arguments objects
function example() {
  return flatten(arguments);
}
example(1, [2, 3], [[4]]);
// Result: [1, 2, 3, [4]]

// Support for objects with Symbol.isConcatSpreadable
const spreadable = { 0: 'a', 1: 'b', length: 2, [Symbol.isConcatSpreadable]: true };
flatten([1, spreadable, 3]);
// Result: [1, 'a', 'b', 3]

null or undefined are treated as empty arrays.

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

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

Parameters

• array (ArrayLike<T> | null | undefined): The array to flatten.

Returns

(T[]): Returns a new flattened array.