WP AJAX fetch

fetch.js

(function() {
  const data = new FormData();
  data.append('action', 'fetch_action');
  data.append('nonce', FETCH.nonce);

  fetch(FETCH.ajax_url, {
    method: "POST",
    credentials: 'same-origin',
    body: data
  })
  .then(response => response.json())
  .then(data => {
    console.log(data);
  })
  .catch(error => console.error(error));
}());

fetch.php

<?php

define('NONCE_ACTION', 'fetch_nonce');

// Load JS
enqueue_js('fetch', 'fetch.js');
wp_localize_script('fetch', 'FETCH', [
  'ajax_url' => admin_url('admin-ajax.php'),
  'nonce' => wp_create_nonce(NONCE_ACTION)
]);


// Define AJAX action
function fetch_action()
{
  $verified = isset($_POST['nonce']) && $_POST['nonce'] && wp_verify_nonce($_POST['nonce'], NONCE_ACTION);

  // Processing
  wp_send_json($_POST);
}
add_action('wp_ajax_fetch_action', 'fetch_action');
add_action('wp_ajax_nopriv_fetch_action', 'fetch_action');