NoteCat/public/index.php

<?php
declare(strict_types=1);

require_once __DIR__ . '/../vendor/autoload.php';

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Slim\Factory\AppFactory;

use NoteCat\HelloWorld;

$app = AppFactory::create();

$app->get('/', function (Request $request, Response $response, $args) {
    $hello = new HelloWorld();
    $response->getBody()->write('<b>' . $hello->getHello() . "</b>\n");
    return $response;
});

$app->run();