What does 'return $next($request)' do in Laravel middleware?

Question

Please respect that I'm new to programming and Laravel, so this question might seem a little odd to the most of you.
But I think this is what stackoverflow is for, so:

When I created a new middleware with the command php artisan make:middleware setLocale there was already the handle-function with this code in it:

return $next($request);

and I'm wondering what exactly this line does.

Answer 1

$next($request) just passes the request to next handler. Suppose you added a middleware for checking age limit.

public function handle($request, Closure $next)
{
    if ($request->age <= 18) {
        return redirect('home');
    }

    return $next($request);
}

when age is less than 18 it will redirect to home but when the request passes the condition what should be done with the request? it will pass it to next handler.Probably to the register user method or any view.

Answer 2

This is explained in the documentation:

To pass the request deeper into the application (allowing the middleware to "pass"), call the $next callback with the $request.

It's best to envision middleware as a series of "layers" HTTP requests must pass through before they hit your application. Each layer can examine the request and even reject it entirely.

https://laravel.com/docs/5.8/middleware#defining-middleware