[Alexandroppolus]

function isValid(str) {
  const pairs = {
    '(': ')',
    '{': '}',
    '[': ']'
  };
  const closes = Object.values(pairs);

  const stack = [];

  for (let s of str) {
    if (pairs[s]) {
      stack.push(pairs[s]);
    } else if (closes.includes(s) && s !== stack.pop()) {
      return false;
    }
  }

  return !stack.length;
}