MatthewTrout

import { flatten } from "./flatten";

test('flatten works', () => {

    expect(
        flatten(
            [1, 2, [3, 4, 5], 6, [7], 8, 9, 10]
        )
    ).toEqual(
        [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

MatthewTrout

export const flatten = (arr) => {
    return arr.reduce((acc, curr) => {
        const val = Array.isArray(curr) ? flatten(curr) : [curr];
        return [...acc, ...val];
    }, []);
};