Ajax WP OOP habrahabr.ru/company/dataart/blog/271189/

AJAX_Handler.php

abstract class AJAX_Handler {

    function __construct($action_name) {
        $this->init_hooks($action_name);
    }

    public function init_hooks($action_name) {
        add_action('wp_ajax_'.$action_name       , array($this,'callback'));
        add_action('wp_ajax_nopriv_'.$action_name, array($this,'callback_nopriv'));
    }

    public function callback_nopriv() {
        $this->callback();
    }

    abstract public function callback();

}

function.php

new Something('do_something');

function js_variables() {
    $variables = array (
        'ajax_url' => admin_url('admin-ajax.php'),
        'is_mobile' => wp_is_mobile()
        // Тут обычно какие-то другие переменные
    );
    echo '<script type="text/javascript">window.wp_data = ' . json_encode($variables) . ';</script>';
}
add_action('wp_head', 'js_variables');

script.js

jQuery(function($){
        $.ajax({
            type: "GET",
            dataType: 'json',
            url: window.wp_data.ajax_url,
            data: {
                action : 'do_something'
            },
            success: function (response) {
                console.log('AJAX response : ',response);
            }
        });
    });

Something.php

<?php
class Something extends AJAX_Handler
{
    function callback ()
    {
        wp_send_json_success(['test' => 'Works!']);
    }
}