Симметричная разница массива

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)
];

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))];
};

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]

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