WordPress Admin AJAX Example

functions.php

<?php
add_action('wp_ajax_action_name', 'callback_function');
add_action('wp_ajax_nopriv_action_name', 'callback_function');

function callback_function() {
	echo 'stuff to return';
	die();
}

main.js

var data = {
	action: 'action_name'
};


$.ajax({
    url: ajaxurl, // http://yoursite.com/wp-admin/admin-ajax.php
    type: "POST",
    data: data,
    async : false,
    success: function(data){
        do_stuff();
    }, 
    fail: function(){
        error_message();
    }
});