Faster Ajax For WordPress

WordPress as a nice API to handle Ajax requests but for some cases its a major overload to include the whole WordPress environment for simple things, So instead define your own light-weight version of an ajax handler:

<?php
//mimic the actual admin-ajax
define('DOING_AJAX', true);

if (!isset( $_POST['action']))
    die('-1');

ini_set('html_errors', 0);

//make sure we skip most of the loading which we might not need
//http://core.trac.wordpress.org/browser/branches/3.4/wp-settings.php#L99
define('SHORTINIT', true);

//make sure you update this line 
//to the relative location of the wp-load.php
require_once('../../../../../wp-load.php'); 

//Typical headers
header('Content-Type: text/html');
send_nosniff_header();

//Disable caching
header('Cache-Control: no-cache');
header('Pragma: no-cache');

//Include only the files and function we need
require( ABSPATH . WPINC . '/formatting.php' );
require( ABSPATH . WPINC . '/meta.php' );
require( ABSPATH . WPINC . '/post.php' );
wp_plugin_directory_constants();

//and do your stuff

But this is for very specific stuff when you know where are the functions you need are located and their dependencies, to know which files to include.

But if you don't (which is usually my case) here is a more generic version of a custom ajax handler:

<?php
//mimic the actuall admin-ajax
define('DOING_AJAX', true);

if (!isset( $_POST['action']))
    die('-1');

//make sure you update this line 
//to the relative location of the wp-load.php
require_once('../../../../../wp-load.php'); 

//Typical headers
header('Content-Type: text/html');
send_nosniff_header();

//Disable caching
header('Cache-Control: no-cache');
header('Pragma: no-cache');

Just about the same but the file inclusion is done for us.

Next we need to call the actual methods we want to invoke so:

$action = esc_attr(trim($_POST['action']));

//A bit of security
$allowed_actions = array(
    'my_allow_action_1',
    'my_allow_action_2',
    'my_allow_action_3',
    'my_allow_action_4',
    'my_allow_action_5'
);

if(in_array($action, $allowed_actions)){
    if(is_user_logged_in())
        do_action('MY_AJAX_HANDLER_'.$action);
    else
        do_action('MY_AJAX_HANDLER_nopriv_'.$action);
}
else{
    die('-1');
}

So altogether we get MYCUSTOMAJAX.php:

<?php
//mimic the actuall admin-ajax
define('DOING_AJAX', true);

if (!isset( $_POST['action']))
    die('-1');

//make sure you update this line 
//to the relative location of the wp-load.php
require_once('../../../../../wp-load.php'); 

//Typical headers
header('Content-Type: text/html');
send_nosniff_header();

//Disable caching
header('Cache-Control: no-cache');
header('Pragma: no-cache');


$action = esc_attr(trim($_POST['action']));

//A bit of security
$allowed_actions = array(
    'my_allow_action_1',
    'my_allow_action_2',
    'my_allow_action_3',
    'my_allow_action_4',
    'my_allow_action_5'
);

if(in_array($action, $allowed_actions)){
    if(is_user_logged_in())
        do_action('MY_AJAX_HANDLER_'.$action);
    else
        do_action('MY_AJAX_HANDLER_nopriv_'.$action);
}
else{
    die('-1');
} 

Next we Only need to hook our callbacks to this handler like so:

//For logged in users
add_action('MY_AJAX_HANDLER_{$action_name}','function_callback_name');
//For logged out users
add_action('MY_AJAX_HANDLER_nopriv_{$action_name}','function_callback_name');

And all that is left is to simply call make your ajax request to this newly created file, like this:

jQuery(document).ready(function($){
    var data={
         action:'action_name',
         otherData: 'otherValue'
    };
    $.post('http://url/to/your/MY_CUSTOM_AJAX.php', data, function(response){
         alert(response);
    });
});

Enjoy The speed!