Fast AJAX handler for wp

ajax.php

<?php
/**
 * Hello, this is a minimal ajax handler for WP.  
 * Based off of: https://coderwall.com/p/of7y2q/faster-ajax-for-wordpress which didn't work for me out of the box.
 * Note: replace tld with your own prefix.
 * Handles get and post type requests.
 * Assumes you put this file in the root directory of your theme folder.
 */

$_tld_ajax = [];

function get_sanitized_action() {
    return filter_var(
        ((!empty($_GET['action'])) ? $_GET['action'] : $_POST['action']),
        FILTER_SANITIZE_STRING
    );
}

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

if (!isset($_POST['action']) && !isset($_GET['action'])) {
    die('-1');
}

$_tld_ajax['action'] = get_sanitized_action();

//A bit of security
$_tld_ajax['allowed_actions'] = [
    // Only allow actions we know about
    'blog_archive'
];

if(!in_array($_tld_ajax['action'], $_tld_ajax['allowed_actions'])){
    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');

if(is_user_logged_in()) {
    do_action("tld_ajax_{$_tld_ajax['action']}");
} else {
    do_action("tld_ajax_nopriv_{$_tld_ajax['action']}");
}

// EOF

To use this, just define your ajax handler functions as normal, and then hook them to the actions you see below in the do_action() calls.

eg:

function my_ajax_function() {
  ...
}

add_action('tld_ajax_my_handler', 'my_ajax_function');
add_action('tld_ajax_nopriv_my_handler', 'my_ajax_function');

// somewhere in javascript:
$.ajax('/wp-content/themes/{theme_name}/ajax.php', {'action' => 'my_action'});