flatMapDeep (Lodash Compatibility)

Use flatMapDeep from es-toolkit

This flatMapDeep function operates slowly due to complex collection type handling and deep flattening logic.

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

Applies a function to each element and recursively flattens the result.

const result = flatMapDeep(collection, iteratee);

Reference

flatMapDeep(collection, iteratee)

Applies an iteratee function to each element of a collection and returns an array flattened to infinite depth. All nested array structures are flattened into a one-dimensional array.

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

// Apply a function to an array and deeply flatten
function duplicate(n) {
  return [[[n, n]]];
}
flatMapDeep([1, 2], duplicate);
// Result: [1, 1, 2, 2]

// Apply a function to an object and deeply flatten
const obj = { a: 1, b: 2 };
flatMapDeep(obj, (value, key) => [[[key, value]]]);
// Result: ['a', 1, 'b', 2]

// Map with a string property and deeply flatten
const users = [
  { user: 'barney', hobbies: [['hiking', 'coding']] },
  { user: 'fred', hobbies: [['reading']] },
];
flatMapDeep(users, 'hobbies');
// Result: ['hiking', 'coding', 'reading']

Using without an iteratee recursively flattens the values.

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

const obj = { a: [[1, 2]], b: [[[3]]] };
flatMapDeep(obj);
// Result: [1, 2, 3]

Conditional mapping with a partial object is also possible.

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

const users = [
  { user: 'barney', active: [true, false] },
  { user: 'fred', active: [false] },
];
flatMapDeep(users, { active: [false] });
// Result: [true, true] (matching result of elements with active array containing [false])

Parameters

• collection (object | null | undefined): The collection to iterate over. Can be an array, object, or string.
• iteratee (ListIterator | ObjectIterator | string | object, optional): The iteratee to apply to each element. Can be a function, property name, or partial object.

Returns

(any[]): Returns a new array recursively flattened after mapping.