flatMap

INFO

This function is only available in es-toolkit/compat for compatibility reasons. It either has alternative native JavaScript APIs or isn't fully optimized yet.

When imported from es-toolkit/compat, it behaves exactly like lodash and provides the same functionalities, as detailed here.

Maps each element in the collection using the iteratee function and flattens the result by one level. The iteratee is invoked with three arguments: (value, index, array).

Signature

function flatMap<T, R>(
  collection: Array<T> | Record<string, T> | null | undefined,
  iteratee?: (
    value: T,
    index: number | string,
    collection: Array<T> | Record<string, T>
  ) => R | Array<R> | null | undefined
): Array<R>;

Parameters

• collection: The collection to iterate over.
• iteratee: The function invoked per iteration. Defaults to identity.

Returns

(Array): Returns the new flattened array.

Examples

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

// Basic example with a function that returns arrays
function duplicate(n) {
  return [n, n];
}

flatMap([1, 2], duplicate);
// => [1, 1, 2, 2]

// Using with property shorthand
const objects = [{ a: [1, 2] }, { a: [3, 4] }];
flatMap(objects, 'a');
// => [1, 2, 3, 4]

// With objects
flatMap({ a: 1, b: 2 }, n => [n, n]);
// => [1, 1, 2, 2]

// Working with arrays of arrays
flatMap([[1], [2, [3]], 4]);
// => [1, 2, [3], 4]