Jquery and scope issues with $.post - ajax

Question

I am having one small problem with my code. I am sending a POST request to my page, after I am done it should return "OK" meaning it worked. From inside my handler function I call set_var(data) to set my global variables text, but the problem is my print_info() returns undefined.
I've spent a lot of time on this and realize my problem has to do with scoping somehow but I am not sure how to go about fixing it. If anyone can provide any pointers, that would be great.
<?
if($_REQUEST['action'] == 'test')
{
echo "OK";
die;
}
?>
<script type="text/javascript" src="jquery-1.6.1.js" ></script>
<script type="text/javascript">
var ajax_post_result;
function set_var(data)
{
//PRINTS MY TEXT OK
alert("SET:: " + data);
//SET TO MY GLOBAL VARIABLE
ajax_post_result = data;
//ALSO PRINTS OK
alert("SET2:: " + ajax_post_result);
}
function return_handler(data, textStatus)
{
//THESE BOTH WORK ... BUT ONLY HERE AND WITHIN set_var()
//alert("1: " + data); //PRINTS WHAT I NEED
//CALL FUNCTION TO SET GLOBAL VARIABLE
set_var(data);
}
function print_info()
{
return ajax_post_result;
}
function ajax_post(file, data )
{
$.post( file, data, return_handler);
//PRINTS UNDEFINED
alert("RETURN:: " + print_info() );
}
</script>
<form id=newform name='testform'>
<input type="hidden" name="newexample" value="1">
Enter Something: <input name="something" id='something1' value="" type="text">
<input type="button" value="Submit" name="Submit" onclick="ajax_post('index.php?action=test', $('#newform').serialize() ); return false;">
</form>

Answer 1

AJAX requests are, as evidenced by the first A in the acronym, asynchronous. So, when you call $.post(), execution of the ajax_post function continues on its merry way more or less immediately, without waiting for the request to finish. You get to your "RETURN" alert before your return_handler has run to set the global variable.
You can use jQuery.ajax and set the async option to false, which will get you a synchronous request.
Or, and I recommend this strategy, move all the things that need to happen only after the request is done to the success handler.

Answer 2

Your problem is due to the asynchronous nature of AJAX.
You should do all your post AJAX processing in the callback function. Something like this (using your current functions)
$.post(file, data, function(data, textstatus) {
return_handler(data, textstatus);
alert("RETURN:: " + print_info());
});
Though you could easily combine your functions into the one closure (minus the alerts), eg
$.post(file, data, function(data, textstatus) {
ajax_post_result = data;
});