Html-refer, what kind and how to find out?

Question

HTTP Cookies

Hello, I need to find out what kind of referrer will be when switching from the application
How will it be displayed when issuing statistics on any sites
or is there some kind of service that issues a link, I insert it in the right place and it shows where I came from

Answer 1

solved the problem

<button type="button" onclick="alert(document.referrer)">адрес предшествующей страницы</button>

does not show the previous page, if anyone knows another option, or knows how the messenger referrer is displayed, tell