use Mojolicious::Lite;

app->hook(after_render => sub {
    my ($c, $output, $format) = @_;

    ${$output} = "Joy<br>$$output<br>Yay";
}); 

get '/' => sub {
    my $self = shift;
 
    warn($self->app->renderer->template_for($self));

    $self->stash(name => $self->param("name"));

    $self->render;
} => "slash";
 
app->start;
 
__DATA__
 
@@ slash.html.ep
Hello, world<%= stash('name') ? ": " . stash('name') : '' %>.
%= form_for "/" => begin
    Name:
    %= text_field "name"
    %= submit_button
% end