Start of main content## Recommended snippets

Returns the symmetric difference between two arrays, using a provided function as a comparator.

- Use
`Array.prototype.filter()`

and`Array.prototype.findIndex()`

to find the appropriate values.

```
const symmetricDifferenceWith = (arr, val, comp) => [
...arr.filter(a => val.findIndex(b => comp(a, b)) === -1),
...val.filter(a => arr.findIndex(b => comp(a, b)) === -1)
];
```

```
symmetricDifferenceWith(
[1, 1.2, 1.5, 3, 0],
[1.9, 3, 0, 3.9],
(a, b) => Math.round(a) === Math.round(b)
); // [1, 1.2, 3.9]
```

### Mapped array symmetric difference

JavaScript, Array

Returns the symmetric difference between two arrays, after applying the provided function to each array element of both.

### Mapped array difference

JavaScript, Array

Returns the difference between two arrays, after applying the provided function to each array element of both.

### Array union based on function

JavaScript, Array

Returns every element that exists in any of the two arrays at least once, using a provided comparator function.