es-toolkit/docs/reference/array/flatMapDeep.md

flatMapDeep

Map each element of a nested array to the given iteratee function, then unpack and flatten all depths.

It works the same as if you called Array#flat with Array#map as map(iteratee).flat(Infinity) in the JavaScript language, but it's faster.

Signature

function flattenDeep<T>(arr: T[]): Array<ExtractNestedArrayType<T>>;

Parameters

• arr (T[]): The array to flatten.
• iteratee (T[]): A function that maps each array element.

Returns

(Array<ExtractNestedArrayType<T>>): A new array with each element mapped and all depths flattened.

Examples

const array = [1, 2, 3];

const result1 = flatMapDeep(array, item => [item, item]);
// Return [1, 1, 2, 2, 3, 3]

const result2 = flatMapDeep(array, item => [[item, item]]);
// Return [1, 1, 2, 2, 3, 3]

const result3 = flatMapDeep(array, item => [[[item, item]]]);
// Return [1, 1, 2, 2, 3, 3]