Shortly Url Shortner Using Vanilla JS

Hi guys, okay so i couldn't get the copy functionality for the link to work since most of the tutorials i could find online referred to an old document.execCommand() which is getting dumped by most browsers so if anybody knows a good way of getting this to work then do give me some suggestions. Also did i write the js properly or did i just overkill everything? And the screenshot seems to mess up so maybe look at the actual site and not the screenshot.