flatMap (Lodash Compatibility)

Use flatMap from es-toolkit

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

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

Applies a function to each element and flattens the result.

const result = flatMap(collection, iteratee);

Reference

flatMap(collection, iteratee)

Applies an iteratee function to each element of a collection and returns an array flattened by one level. Supports arrays, objects, and strings, and can use various forms of iteratees.

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

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

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

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

Using without an iteratee flattens the values by one level.

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

const obj = { a: [1, 2], b: [3, 4] };
flatMap(obj);
// Result: [1, 2, 3, 4]

Conditional mapping with a partial object is also possible.

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

const users = [
  { user: 'barney', age: 36, active: true },
  { user: 'fred', age: 40, active: false },
];
flatMap(users, { active: false });
// Result: [false, true] (matching result of elements where active is 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 flattened by one level after mapping.