DiffTwoArrays.js

// Compare two arrays and return a new array with any items only found 
// in one of the two given arrays, but not both.In other words, return 
// the symmetric difference of the two arrays.

function diffArray(arr1, arr2) {
  const difference = []

  arr1.forEach((item) => {
    if (!arr2.includes(item)) {
      difference.push(item)
    }
  })

  arr2.forEach((item) => {
    if (!arr1.includes(item)) {
      difference.push(item)
    }
  })

  return difference
}

diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);

// diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]) should return an array.
// ["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"] should return ["pink wool"].
// ["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"] should return an array with one item.
// ["andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"] should return ["diorite", "pink wool"].
// ["andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"] should return an array with two items.
// ["andesite", "grass", "dirt", "dead shrub"], ["andesite", "grass", "dirt", "dead shrub"] should return [].
// ["andesite", "grass", "dirt", "dead shrub"], ["andesite", "grass", "dirt", "dead shrub"] should return an empty array.
// [1, 2, 3, 5], [1, 2, 3, 4, 5] should return [4].
// [1, 2, 3, 5], [1, 2, 3, 4, 5] should return an array with one item.
// [1, "calf", 3, "piglet"], [1, "calf", 3, 4] should return ["piglet", 4].
// [1, "calf", 3, "piglet"], [1, "calf", 3, 4] should return an array with two items.
// [], ["snuffleupagus", "cookie monster", "elmo"] should return ["snuffleupagus", "cookie monster", "elmo"].
// [], ["snuffleupagus", "cookie monster", "elmo"] should return an array with three items.
// [1, "calf", 3, "piglet"], [7, "filly"] should return [1, "calf", 3, "piglet", 7, "filly"].
// [1, "calf", 3, "piglet"], [7, "filly"] should return an array with six items.