<update> Your Mother beat me to it by seconds :-) </update>
IMHO, the best way nowadays is JavaScript:
#!/usr/bin/env perl
use Mojolicious::Lite -signatures;
get '/' => sub ($c) {
$c->render(template => 'index');
} => 'index';
get '/dynupd' => sub ($c) {
$c->render(json => { time => time });
} => 'dynupd';
app->start;
__DATA__
@@ layouts/main.html.ep
<!DOCTYPE html>
<html>
<head><title><%= title %></title></head>
<body>
%= content
</body>
</html>
@@ index.html.ep
% layout 'main', title => 'Hello, World!';
<div>Hello, World!</div>
<div id="dyn_upd">Fetching, please wait...</div>
<script src="https://code.jquery.com/jquery-3.4.1.min.js"
integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo="
crossorigin="anonymous"></script>
<script>
function updateDynamic() {
$.ajax({ url: '<%= url_for('dynupd') %>', timeout: 1000 })
.done( function( data ) {
$('#dyn_upd').text(data.time);
})
.fail( function( jqXHR, textStatus, errorThrown ) {
$('#dyn_upd').text("Update Failed: "+textStatus
+" / "+jqXHR.status+" "+errorThrown);
});
}
$(function () {
updateDynamic();
setInterval(updateDynamic, 2000);
});
</script>