Ajax :: Script To Get Results From Database Returns Undefined

I'm new to ajax. I've made a script that should return results from database but it keeps telling me just undefined. Code what I have:

Code:
var ajax = null;
function showRes(wut) {
if(wut.length == 0) {
document.getElementById("results").innerHTML = "";
return;
} if(window.XMLHttpRequest) {
// IE7+, ff, chrome, opera, safari
ajax = new XMLHttpRequest();
}else if(window.ActiveXObject) {
// retards
ajax = new ActiveXObject("Microsoft.XMLHTTP");
} else {
alert("Your "browser" does not support AJAX!");
return;
} var url = "search.php?q=" + wut;
url = url + "&sid=" + Math.random();
ajax.open("GET", url, true);
ajax.send(null);
document.getElementById("results").innerHTML = ajax.reponseText;
}