Implementation of Array flattening with JavaScript

array_flattening.md

This gist discusses the implementation of Array flattening with JavaScript. It returns a single array with all of its element recursively flattened.

To Run Test

  node flat_array_test.js

flat_array.js

const flat = array => {
  let collector = [];
  if (!(array instanceof Array)) {
    throw new Error('Not an array');
  }
  for (let elem of array) {
    if (elem instanceof Array) {
      collector = [...collector, ...flat(elem)];
    } else {
      collector = [...collector, elem];
    }
  }
  return collector;
};
module.exports = flat;

flat_array_test.js

const flat = require('./flat_array');
const { assertDeepEqual, shouldThrow } = require('./test');

assertDeepEqual(
  flat([1, 2, 3, [4, 5, [6, 7, 8, [9, 10]]], 11, 12, [13, 14]]),
  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14],
  'Should flatten all nested arrays into a single one'
);

assertDeepEqual(
  flat([1, 2, 3, [4, 5, [6, 7, 8, [9, 10]]]]),
  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
  'Should flatten all nested arrays into a single one 2'
);

assertDeepEqual(
  flat([1, 2, 3]),
  [1, 2, 3],
  'Should return the same array if it is flattened already'
);
assertDeepEqual(flat([]), [], 'Return an empty array if the input is empty');

assertDeepEqual(flat([1, 2, 3, []]), [1, 2, 3], 'Ignore empty array');

shouldThrow(() => flat(1), 'Should throw an error if input is not an array');

test.js

// Simple Test Library

function assertEq(left, right, info = '') {
  if (left !== right) {
    console.error(`Test Failed ❗️:
    Expected =>  ${right}
    Got => ${left}`);
  } else {
    console.log(`Test: ${info} Passed`);
  }
}
function assertDeepEqual(left, right, info = '') {
  if (!left.every((e, i) => e === right[i])) {
    console.error(`Test Failed:
    Expected =>  ${right}
    Got => ${left}\n`);
  } else {
    console.log(`\n${info}: Passed ✅\n`);
  }
}
function shouldThrow(cb, info = '') {
  let hasthrown = false;
  try {
    cb();
  } catch (error) {
    hasthrown = true;
    console.log(`\n${info}: Passed ✅\n`);
  } finally {
    if (!hasthrown) {
      console.error(`Test Failed: Didn't throw an error\n`);
    }
  }
}

module.exports = { assertEq, assertDeepEqual, shouldThrow };