Add “http://” or “https://” to a URL that contain only the relative url starting by “www” or not

Dear all,

I am using the script below for reading an url and automatically add to one the "Protocol" Http or Https.  The script below reading only https or http, because I cannot add another ELSE IF. This script is good for any url starting by "www", but many urls don´t starting by "www". So I have 2 problems. Could someone help me to improve this code for adding automatically the protocol and independetly if starts or not by 'www'?


<script>
function formatURL()
{
var url = document.getElementsByName("URL")[0];
var formattedURL = document.getElementsByName("formattedURL")[0];
url = url.value;
if(url.substr(0,3) === "www") // it is for an url starting by www but I need for urls starting or not by www
{
formattedURL.value = "http://"+url;

return;
}

// I need here other alternative to https:
}
formattedURL.value = url;
}
</script>

The results are reading by a form that "convert" the url without http or https with www or without www to real url to open it in another screen

Sorry by the inconveniences

Sincerely

Letchev