ajax 질문입니다..

function myFunction(){

alert("aa");

var memberID = document.getElementById("memberID");

var memberHP = document.getElementById("memberHP");

xmlhttp = new XMLHttpRequest(); 

xmlhttp.open("GET","/memberHP.php?qMemberId="+userid.value,true);

xmlhttp.send();

xmlhttp.onreadystatechange=function(){

if(xmlhttp.readyState==4 && xmlhttp.status ==200){

memberHP.innerHTML = xmlhttp.responseText;

}

}

왜 alert도 반응을 안할까요? ㅠ.ㅠ