6. symmetric

const symmetricSet = (setA, setB) => { // getting two sets from function
  const symmetricSet = new Set();  // creating a new set

  setA.forEach(element => {    // checking each element of the first set if it is in the second set
    if(!setB.has(element)) {
      symmetricSet.add(element);
    };
  });

  setB.forEach(element => {  // same
    if(!setA.has(element)){
      symmetricSet.add(element);
    };
  });

  return Array.from(symmetricSet);  // returning the set as an array
}

const setX = new Set([1, 2, 3, 4, 5]);
const setY = new Set([4, 5, 6, 7, 8]);

console.log(symmetricSet(setX, setY)); // [ 1, 2, 3, 6, 7, 8 ]