freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/diff-two-arrays.md

---
id: a5de63ebea8dbee56860f4f2
title: Diff Two Arrays
challengeType: 5
forumTopicId: 16008
dashedName: diff-two-arrays
---

# --description--

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.

**Note:** You can return the array with its elements in any order.

# --hints--

`diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5])` should return an array.

```js
assert(typeof diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]) === 'object');
```

`["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"]` should return `["pink wool"]`.

```js
assert.sameMembers(
  diffArray(
    ['diorite', 'andesite', 'grass', 'dirt', 'pink wool', 'dead shrub'],
    ['diorite', 'andesite', 'grass', 'dirt', 'dead shrub']
  ),
  ['pink wool']
);
```

`["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"]` should return an array with one item.

```js
assert(
  diffArray(
    ['diorite', 'andesite', 'grass', 'dirt', 'pink wool', 'dead shrub'],
    ['diorite', 'andesite', 'grass', 'dirt', 'dead shrub']
  ).length === 1
);
```

`["andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"]` should return `["diorite", "pink wool"]`.

```js
assert.sameMembers(
  diffArray(
    ['andesite', 'grass', 'dirt', 'pink wool', 'dead shrub'],
    ['diorite', 'andesite', 'grass', 'dirt', 'dead shrub']
  ),
  ['diorite', 'pink wool']
);
```

`["andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"]` should return an array with two items.

```js
assert(
  diffArray(
    ['andesite', 'grass', 'dirt', 'pink wool', 'dead shrub'],
    ['diorite', 'andesite', 'grass', 'dirt', 'dead shrub']
  ).length === 2
);
```

`["andesite", "grass", "dirt", "dead shrub"], ["andesite", "grass", "dirt", "dead shrub"]` should return `[]`.

```js
assert.sameMembers(
  diffArray(
    ['andesite', 'grass', 'dirt', 'dead shrub'],
    ['andesite', 'grass', 'dirt', 'dead shrub']
  ),
  []
);
```

`["andesite", "grass", "dirt", "dead shrub"], ["andesite", "grass", "dirt", "dead shrub"]` should return an empty array.

```js
assert(
  diffArray(
    ['andesite', 'grass', 'dirt', 'dead shrub'],
    ['andesite', 'grass', 'dirt', 'dead shrub']
  ).length === 0
);
```

`[1, 2, 3, 5], [1, 2, 3, 4, 5]` should return `[4]`.

```js
assert.sameMembers(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]), [4]);
```

`[1, 2, 3, 5], [1, 2, 3, 4, 5]` should return an array with one item.

```js
assert(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]).length === 1);
```

`[1, "calf", 3, "piglet"], [1, "calf", 3, 4]` should return `["piglet", 4]`.

```js
assert.sameMembers(diffArray([1, 'calf', 3, 'piglet'], [1, 'calf', 3, 4]), [
  'piglet',
  4
]);
```

`[1, "calf", 3, "piglet"], [1, "calf", 3, 4]` should return an array with two items.

```js
assert(diffArray([1, 'calf', 3, 'piglet'], [1, 'calf', 3, 4]).length === 2);
```

`[], ["snuffleupagus", "cookie monster", "elmo"]` should return `["snuffleupagus", "cookie monster", "elmo"]`.

```js
assert.sameMembers(diffArray([], ['snuffleupagus', 'cookie monster', 'elmo']), [
  'snuffleupagus',
  'cookie monster',
  'elmo'
]);
```

`[], ["snuffleupagus", "cookie monster", "elmo"]` should return an array with three items.

```js
assert(diffArray([], ['snuffleupagus', 'cookie monster', 'elmo']).length === 3);
```

`[1, "calf", 3, "piglet"], [7, "filly"]` should return `[1, "calf", 3, "piglet", 7, "filly"]`.

```js
assert.sameMembers(diffArray([1, 'calf', 3, 'piglet'], [7, 'filly']), [
  1,
  'calf',
  3,
  'piglet',
  7,
  'filly'
]);
```

`[1, "calf", 3, "piglet"], [7, "filly"]` should return an array with six items.

```js
assert(diffArray([1, 'calf', 3, 'piglet'], [7, 'filly']).length === 6);
```

# --seed--

## --seed-contents--

```js
function diffArray(arr1, arr2) {
  var newArr = [];
  return newArr;
}

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

# --solutions--

```js
function diffArray(arr1, arr2) {
  var newArr = [];
  var h1 = Object.create(null);
  arr1.forEach(function(e) {
    h1[e] = e;
  });

  var h2 = Object.create(null);
  arr2.forEach(function(e) {
    h2[e] = e;
  });

  Object.keys(h1).forEach(function(e) {
     if (!(e in h2)) newArr.push(h1[e]);
  });
  Object.keys(h2).forEach(function(e) {
     if (!(e in h1)) newArr.push(h2[e]);
  });
  return newArr;
}
```