Flat an array recursively

flatMap.js

const _ = require('lodash');

const x = [1, [2, 3, 4, [5, 6]], 7];

const flat = (input) => Array.isArray(input) ? _.flatMap(input, item => flat(item)) : input;

const y = flat(x)

y // [1, 2, 3, 4, 5, 6, 7]