How Get the absolete URL from a relative url placed into a input form?

Dear all,

Could I get the absolute url from a relative url placed into an input form?

Example:

Input text = "www.elmundo.es"
absolute url = https://www.elmundo.es

Input text = "w3guy.com/relative-absolute-url-guide/"
absolute url = https://w3guy.com/relative-absolute-url-guide/

Input text = "www.filosofia.org/rev/bas/"
absolute url = http://www.filosofia.org/rev/bas/

There are dozens of solutions to get absolute url from a relative url on address bar (the url of the open page), but not from an input form.

I just make a question ultimately!

Could someone help me to find a solution for this case

Thanks