2 * arr-flatten <https://github.com/jonschlinkert/arr-flatten>
4 * Copyright (c) 2014-2017, Jon Schlinkert.
5 * Released under the MIT License.
10 module.exports = function (arr) {
14 function flat(arr, res) {
17 for (; i < len; i++) {
19 Array.isArray(cur) ? flat(cur, res) : res.push(cur);