Flattens an array of arbitrarily nested arrays of integers into a flat array of integers #go

flatten.js

/**
 * Flattens an array of arbitrarily nested arrays of integers
 * into a flat array of integers.
 *
 * @param {array} arr The array to flatten.
 * @returns {array} Flattened array
 */
const flatten = (arr = []) => {
  if (!isArray(arr)) {
    return [];
  }
  let result = [];
  for (let item of arr) {
    if (isArray(item)) {
      result = result.concat(flatten(item));
    } else {
      result = result.concat(item);
    }
  }
  return result;
};

const isArray = (arr) => {
  return arr instanceof Array;
};

exports.flatten = flatten;

flatten_test.js

const test = require('tape');
const flatten = require('../src/flatten').flatten;

test('flatten tests', function (t) {
  t.plan(6);
  // format is {'testName': [input, expected]}
  const tests = {
    'object':[{},[]],
    'empty': [[], []],
    'oneElementDeep': [[1,2,3], [1,2,3]],
    'twoElementsDeep': [[[1,[3,4],5]], [1,3,4,5]],
    'threeElementsDeep': [[1,[2,[3,4],5]], [1,2,3,4,5]],
    'multipleElementsDeep': [[[[1]],2,[3,[3,5],[6,[7,8]]]], [1,2,3,3,5,6,7,8]],
  };

  for (const [key, value] of Object.entries(tests)) {
    t.deepEqual(flatten(value[0]), value[1], key);
  }
});