Flattens a nested array recursively (A quick ES6 prototype of my https://www.npmjs.com/package/flatten-arr)

readme.md

Flattens a nested array recursively

A quick ES6 prototype of my https://www.npmjs.com/package/flatten-arr

Tests

tests are written without a test library, just intrinsice Node.js assert.

yarn test

Gist

https://gist.github.com/wilmoore/579383ea7288b842f522d04c06232007

index.js

const toString = Object.prototype.toString

/**
 * Recursive list item concatenation.
 *
 * @param {Array} nested
 * Nested array.
 *
 * @param {Array} flat
 * Initial/Flattended array.
 *
 * @return {Array}
 * Flattened array.
 */

const concat = (nested, flat) => {
  let end = nested.length
  let idx = -1

  while (++idx < end) {
    if (toString.call(nested[idx]) === '[object Array]') {
      concat(nested[idx], flat)
    } else {
      flat.push(nested[idx])
    }
  }

  return flat
}

/**
 * Flattens a nested array recursively.
 *
 * @param {Array} list
 * Nested array.
 *
 * @return {Array}
 * Flattened array.
 */

exports.flatten = (list) => concat(list, [])

package.json

{
  "name": "gist",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "scripts": {
    "test": "node test"
  }
}

test.js

const assert = require('assert')
const { flatten } = require('./')

{
  const original = [[1, 2, [3]], 4]
  const expected = [1, 2, 3, 4]
  assert.deepEqual(flatten(original), expected)
}

{
  const original = [1, [[[2, [[3, 4]], 5], 6]], [7], [[[8]]], 9]
  const expected = [1, 2, 3, 4, 5, 6, 7, 8, 9]
  assert.deepEqual(flatten(original), expected)
}