FLAT A LIST(ARRAY) USING JAVASCRIPT

solution.js

/*
  A - S I M P L E - F L A T - L I S T - H A N D L E R 
  - U S I N G - F L A T 
*/
const flatListHandler = (nestedArray, depth) => {
  return nestedArray.flat(depth);
}

// U S A G E - 
const nestedArray = [1, 2, 3 ,4 , [5, 6, 7], 8];
const flattenList = flatListHandler(nestedArray, 1);
console.log(flattenList); // 1,2,3,4,5,6,7,8

// NB DEPTH can be 1, 2, 3, 4 and so on 
// if you want to go infinitely deep DEPTH can be set to Infinity 

// Since not all browsers support this there are some couple of alternatives to use
// I've one written in another gist of mine couple of months ago
// https://gist.github.com/samcyn/4997504b6a41fb6d5ae201081f8d5fbc

test.js

// LET SAY YOU HAVE MOCHA AND CHAI SET UP 
// A QUICK WAY TO TEST THIS UTILITY FUNCTION CAN BE AS FOLLOWS
import { assert } from 'chai';
import flatListHandler from './solution';

const nestedArray = [[1,2,[3]],4];
describe('Basic Mocha String Test', function () {
 it('should return flat list', function () {
     assert.deepEqual(flatListHandler(nestedArray), [1,2,3,4]);
  });
});