### symmetricDifference

Returns the symmetric difference between two arrays.

Create a `Set` from each array, then use `Array.filter()` on each of them to only keep values not contained in the other.

```js
const symmetricDifference = (a, b) => {
  const sA = new Set(a),
    sB = new Set(b);
  return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
};
```

```js
symmetricDifference([1, 2, 3], [1, 2, 4]); // [3,4]
```