判断对号的有效性之[{()}]

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    var stack= [];
    var sArr= s.split("");
    var symObj= {"}": "{", "]": "[", ")":")"};
    while(sArr.length){
        var head= sArr.shift();
        switch(head){
            case '(':
            case '{':
            case '[':
                stack.push(head);
            break;
            case ')':
            case '}':
            case ']':
                if(stack.pop() !== symObj[head]){
                    return false;
                }
            break;
        }
    }
    return stack.length === 0
};