//設置cookie
function setCookie(key, value) {
        document.cookie = key + "=" + escape(value);
}
//獲取cookie的值
    function getCookie(key) {
        if (document.cookie.length) {
            var cookies = ' ' + document.cookie;
            var start = cookies.indexOf(' ' + key + '=');
            if (start == -1) { return null; }
            var end = cookies.indexOf(";", start);
            if (end == -1) { end = cookies.length; }
            end -= start;
            var cookie = cookies.substr(start,end);
            return unescape(cookie.substr(cookie.indexOf('=') + 1, cookie.length - cookie.indexOf('=') + 1));
        }
        else { return null; }
    }   

//根據點擊傳進來的id
function comment(id,is){
     if(getCookie(id)==null){
           setCookie(id,"           alert("設置cookie成功");
       }else{
           if(getCookie(id)=="               alert("您已經點評過了");
               return ;
        }
 //這里是你自己的邏輯 通過ajax保存到數據庫的數值
}