Laravel project gives Undefined property error when run php artisan serve command

I have a Laravel project,
this code from routes/web.php

$router->get('/', function () use ($router) {
    return $router->app->version();
});

When I try to run ‘php artisan serve’ it gives Undefined property: Illuminate\Routing\Router::$app error,

I tried adding container instead of app

$router->get('/', function () use ($router) {
    return $router->container->version();
});

then it gives ‘Error: cannot access protected property’
Please let me know if anyone knows how to clear this issue and run the project

ErrorException: Undefined property: Illuminate\Routing\Router::$app

at /Applications/XAMPP/xamppfiles/htdocs/em2/routes/web.php:18 at Illuminate\Foundation\Bootstrap\HandleExceptions->handleError(8, 'Undefined property: Illuminate\Routing\Router::$app', '/Applications/XAMPP/xamppfiles/htdocs/em2/routes/web.php', 18, array('router' => object(Router))) (/Applications/XAMPP/xamppfiles/htdocs/em2/routes/web.php:18) at Illuminate\Routing\RouteFileRegistrar->{closure}()

>Solution :

use app() helper method to access app instance from anywhere. try this

$router->get('/', function () {
    return app()->version();
});