uniqueSymmetricDifference

Returns the unique symmetric difference between two arrays, not containing duplicate values from either array.

• Use Array.prototype.filter() and Array.prototype.includes() on each array to remove values contained in the other.
• Create a new Set() from the results, removing duplicate values.

const uniqueSymmetricDifference = (a, b) => [
  ...new Set([
    ...a.filter(v => !b.includes(v)),
    ...b.filter(v => !a.includes(v)),
  ]),
];

uniqueSymmetricDifference([1, 2, 3], [1, 2, 4]); // [3, 4]
uniqueSymmetricDifference([1, 2, 2], [1, 3, 1]); // [2, 3]