Balanced parentheses solution with implicit state

implicit.js

function balanced (string) {
  const iterator = string[Symbol.iterator]();
  
  return balancedIterator(iterator) === true;
}

const CLOSE = {
  '(': ')',
  '[': ']',
  '{': '}'
};

function balancedIterator(iterator) {
  while (true) {
    const { value: token, done } = iterator.next();

    if (done) {
      return true;
    } else if (!!CLOSE[token]) {
      const nextToken = balancedIterator(iterator);

      if (nextToken !== CLOSE[token]) {
        return false;
      }
    } else {
      return token;
    }
  }
}

function test (examples) {
  for (const example of examples) {
    console.log(`'${example}' => ${balanced(example)}`);
  }
}

test(['', '()', '(){}',
  '([()()]())', '([()())())',
  '())()', '((())(())'
]);
  //=>
    '' => true
    '()' => true
    '(){}' => true
    '([()()]())' => true
    '([()())())' => false
    '())()' => false
    '((())(())' => false