Modify outside variable from within AJAX function?

Modify outside variable from within AJAX function?

I use a AJAX request to get a numerical value from the database. The AJAX
function is inside another function that should return the value of the
AJAX request. However because the return value from the AJAX request is a
local variable inside the xmlhttp.onreadystatechange function it doesn't
change the "higher level" temp_return of the return_count function. I
can't have the "lower" function return the value and assign it to a
variable because it's already defined to xmlhttp.onreadystatechange... How
can I change this so that the return_count function will return the
correct value instead of 42 (predefined for testing purposes)?
function return_count(ajax_userid,ajax_date,ajax_KT,ajax_KS)
{
var temp_return = 42;
xmlhttp.onreadystatechange =
function()
{
if(xmlhttp.readyState == 4 && xmlhttp.status == 200)
{
temp_return = xmlhttp.responseText;
}
}
xmlhttp.open("GET",
"count.php?userid="+ajax_userid+"&date="+ajax_date+"&KT="+ajax_KT+"&KS="+ajax_KS,
true);
xmlhttp.send();
return temp_return;
}