如何让wp_ajax与jQuery $ .post一起使用

Question

Straight from WP Codex: http://codex.wordpress.org/AJAX_in_Plugins

I have this in my functions.php:

add_action( 'admin_footer', 'my_action_javascript' );

function my_action_javascript() {
?>
<script type="text/javascript" >
jQuery(document).ready(function($) {

    var data = {
        'action': 'my_action',
        'whatever': 1234
    };

    // since 2.8 ajaxurl is always defined in the admin header and points to admin-ajax.php
    $.post(ajaxurl, data, function(response) {
        alert('Got this from the server: ' + response);
    });
});
</script>
<?php
}
add_action( 'wp_ajax_my_action', 'my_action_callback' );

function my_action_callback() {
    global $wpdb; // this is how you get access to the database

    $whatever = intval( $_POST['whatever'] );

    $whatever += 10;

        echo $whatever;

    die(); // this is required to return a proper result
}

And I don't get a response. I do get an alert saying 'Got this from the server: ', but no response. What gives?