---
title: Diff Two Arrays
---
# Diff Two Arrays
---
## Problem Explanation
Check two arrays and return a new array that contains only the items that are not in either of the original arrays.
#### Relevant Links
* for Loop (Devdocs)
* Array.prototype.includes (Devdocs)
* Array.prototype.filter (Devdocs)
* Array.prototype.concat (Devdocs)
---
## Hints
### Hint 1
Merge the list to make it easy to compare functions.
### Hint 2
Use filter to get the new array, you will need to create a callback function.
### Hint 3
The best way to go about the callback function is to check if the number from the new merged array is not in **both** original arrays and return it.
---
## Solutions
Solution 1 (Click to Show/Hide)
(Imperative Solution)
```javascript
function diffArray(arr1, arr2) {
var newArr = [];
function onlyInFirst(first, second) {
// Looping through an array to find elements that don't exist in another array
for (var i = 0; i < first.length; i++) {
if (second.indexOf(first[i]) === -1) {
// Pushing the elements unique to first to newArr
newArr.push(first[i]);
}
}
}
onlyInFirst(arr1, arr2);
onlyInFirst(arr2, arr1);
return newArr;
}
diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);
```
#### Code Explanation
Read the comments in the code.
#### Relevant Links
* for Loop (Devdocs)
Solution 2 (Click to Show/Hide)
(Declarative Solution):
```javascript
function diffArray(arr1, arr2) {
return arr1
.concat(arr2)
.filter(item => !arr1.includes(item) || !arr2.includes(item));
}
diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);
```
#### Code Explanation
Explain solution here and add any relevant links
#### Relevant Links
* Array.prototype.concat (Devdocs)
* Array.prototype.filter (Devdocs)
* Array.prototype.includes (Devdocs)
Solution 3 (Click to Show/Hide)
(Declarative Solution)
```javascript
function diffArray(arr1, arr2) {
return [...diff(arr1, arr2), ...diff(arr2, arr1)];
function diff(a, b) {
return a.filter(item => b.indexOf(item) === -1);
}
}
```
#### Relevant Links
* Array.prototype.includes (Devdocs)
* Array.prototype.filter (Devdocs)
* Array.prototype.concat (Devdocs)