docs/compat/reference/array/flatten.md
::: warning 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);
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([]); // []
array (ArrayLike<T> | null | undefined): The array to flatten.(T[]): Returns a new flattened array.