JavaScript ES2015 Set equality

set-eqaulity.js

/**
 * 
 * 
 * @param {Set} aaa 
 * @param {Set} bbb 
 * @param {function} [comparator] 
 * @returns {boolean}
 */
function equalSets(aaa, bbb, comparator = (x, y) => x === y) {
  if ('function' !== typeof comparator) {
    throw new TypeError(typeof comparator);
  }
  if (!(aaa instanceof Set) || !(bbb instanceof Set)) return false;
  if (aaa.size !== bbb.size) return false;
  for (const itemA of aaa) {
    let hasB = false;
    for (const itemB of bbb) {
      hasB = comparator(itemA, itemB);
      if (hasB) {
        // Is this more expensive than brute force?
        return equalSets(
          cloneWithout(aaa, itemA),
          cloneWithout(bbb, itemB),
          comparator
        );
      }
    }
    if (!hasB) return false;
  }
  return true;
}

/**
 * Clones a new set with a specific entry.
 * Doesn’t modify `set`.
 * 
 * @param {Set} set 
 * @param {any} entry 
 * @returns {Set}
 * @throws {TypeError}
 */
function cloneWithout(set, entry) {
  if (!(set instanceof Set)) {
    throw new TypeError(String(set));
  }
  const clone = new Set(set);
  if (undefined !== entry) {
    clone.delete(entry);
  }
  return clone;
}