code: function (other) {
          assertNotNull(other);
  
          if (this.count() === 0) {
              this.unionWith(other);
              return;
          }
  
          else if (other === this) {
              this.clear();
              return;
          }
  
          // If other is a HashSet, it has unique elements according to its equality comparer,
          // but if they're using different equality comparers, then assumption of uniqueness
          // will fail. So first check if other is a hashset using the same equality comparer;
          // symmetric except is a lot faster if we can assume uniqueness
  
          if (areEqualityComparersEqual(this, other)) {
              var table = this.table;
  
              forOf(other, function (element) {
                  if (!table.remove(element)) {
                      table.add(element, null);
                  }
              });
          }
          else {
              this.symmetricExceptWith(new HashSet(other, this.comparer));
          }
      }
docs: Modifies the current set so that it contains only elements that are present
  either in the current set or in the specified collection, but not both.
  @param {Iterable} other The collection to compare to the current set.