栈数据结构实现：字符串中括号是否匹配

下文中用到的栈的类：栈类实现

function parenthesesChecker(symbols) {
  const stack = new Stack();
  const opens = '([{';
  const closers = ')]}';
  let balanced = true;
  let index = 0;
  let symbol;
  let top;

  while (index < symbols.length && balanced) {
    symbol = symbols[index];
    if (opens.indexOf(symbol) >= 0) {
      stack.push(symbol);
    } else if (stack.isEmpty()) {
      balanced = false;
    } else {
      top = stack.pop();
      if (!(opens.indexOf(top) === closers.indexOf(symbol))) {
        balanced = false;
      }
    }
    index++;
  }
  return balanced && stack.isEmpty();
}