you could use iframe to serve external and use jquery in your source. There already jQuery js inside appyet. just need to link to it.
Sent from my MI 3W using AppYet
Easy solution is using jquery.ex:
$(document).on('offline online', function (event) {
alert('You are ' + event.type + '!');
//or change background image perhaps
});
Sent from my MI 3W using AppYet