在jquery验证码验证中比较$ .post的值

hi i had written code for captcha validation but it not works, what am i missing

 function validate() {

     $.post("http://localhost/test/captch.php?captcha=" + document.getElementById("captchaid").value, function (data) {
         alert("sss" + data);
         if (data != 'yes') {
             alert("invalid captcha");
             return false;
         }

     });
 }