Simple function to flatten an array of arbitrarily nested arrays of integers into a flat array of integers with tests in ES6

Readme.txt

Set up a simple folder strucure thus:

```
FlattenList
|-src
|  |-index.js
|-test
| |-test.js
|-package.json
```

To run tests: 
simply run: `npm run test`

index.js

// Helper function to flatten a given nested array
export default function flattenList(arr) {
  return arr.reduce((current, next) => current.concat(
    Array.isArray(next) ? flattenList(next) : next), []
  )
};

package.json

{
  "name": "flattenlist",
  "version": "1.0.0",
  "author": "Jyd",
  "description": "Simple function to flatten an arbitrary list of nested array",
  "main": "index.js",
  "scripts": {
    "test": "mocha --compilers js:babel-core/register --recursive",
    "test:watch": "npm run test -- --watch"
  },
  "devDependencies": {
    "babel-cli": "^6.5.1",
    "babel-core": "^6.5.2",
    "babel-preset-es2015": "^6.5.0",
    "mocha": "^2.4.5",
    "chai": "^3.5.0"
  },
  "license": "ISC",
  "babel": {
    "presets": [
      "es2015"
    ]
  }
}

test.js

import flattenList from '../src/index';
import { expect } from 'chai'

describe('Flatten an array', () => {
  const testCaseOne = [[1,2,[3]],4];
  const testCaseTwo = [[1], [2, 3], [4, [5, [6, [7, [8]]]]]];
  
  it('should flatten the nested array for testCaseOne', () => {
    const expected = [1,2,3,4];
    const result = flattenList(testCaseOne);
    expect(result).to.deep.equal(expected);
  });

  it('should flatten the nested array for testCaseTwo', () => {
    const expected = [1,2,3,4, 5,6,7,8];
    const result = flattenList(testCaseTwo);
    expect(result).to.deep.equal(expected);
  });
});