Flat Array

.gitignore

node_modules

flatArray.js

function startFlat(arr) {

  let arrRes = []

  if (!Array.isArray(arr)) {
    return null;
  }

  return flatArray(arr);

  function flatArray(arr) {

    for (let i = 0; i < arr.length; i++) {
      if (Array.isArray(arr[i])) {
        flatArray(arr[i])
      } else {
        arrRes.push(arr[i]);
      }
    }

    return arrRes;
  }
}

module.exports = startFlat;

package.json

{
  "name": "flat-array",
  "version": "1.0.0",
  "description": "",
  "main": "flatArray.js",
  "scripts": {
    "test": "mocha"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "chai": "^3.5.0"
  }
}

test.js

const chai = require('chai');
const flatArray = require('./flatArray');

describe('Array', function() {
  it('Should flat nested arrays', function () {
    const arr = [[1, 2], 3];
    chai.expect(flatArray(arr)).to.eql([1, 2, 3]);
  });

  it('Should return null if the input is not an array', function() {
    chai.assert.equal(flatArray({ foo: 'bar' }), null);
  });

  it('Should flat deep nested array', function() {
    const arr = [
      1,
      [
        [
          2,
          3,
          4,
          [{ five: 'six' }, 'seven'],
          8
        ]
      ],
      9
    ];
    chai.expect(flatArray(arr)).to.eql([1, 2, 3, 4, { five: 'six' }, 'seven', 8, 9]);
  })
});