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, then create a 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]