const validBraces = function(str) {
        // 匹配括号
        let brackets = str.match(/[\[\]\(\)\{\}]/g),
            arr = [],
            symbol;
        for (var i in brackets) {
            switch (brackets[i]) {
                case '(':
                    arr.push('(');
                    break;
                case '[':
                    arr.push('[');
                    break;
                case '{':
                    arr.push('{');
                    break;
                case ')':
                    symbol = arr.pop();
                    if (symbol !== '(') return false;
                    break;
                case ']':
                    symbol = arr.pop();
                    if (symbol !== '[') return false;
                    break;
                case '}':
                    symbol = arr.pop();
                    if (symbol !== '{') return false;
                    break

            }
        }
        // 当存在 (() 这样的情况时, 上面的都能通过, 最后需要检测一下arr的长度
        return arr.length > 0 ? false : true;
    }
    // 测试
console.log(validBraces("(){}[]"));//true
console.log(validBraces("(}"));//false
console.log(validBraces("[(])"));//false
console.log(validBraces("([{}])"));//true

function validBraces(braces){
  var matches = { '(':')', '{':'}', '[':']' };
  var stack = [];
  var currentChar;

  for (var i = 0; i < braces.length; i++) {
    currentChar = braces[i];

    if (matches[currentChar]) { // opening braces
      stack.push(currentChar);
    } else { // closing braces
      if (currentChar !== matches[stack.pop()]) {
        return false;
      }
    }
  }

  return stack.length === 0; // any unclosed braces left?
}

用正则表达式匹配 错误的形式