Regex Full URL -> Base URL

Full url:
http://stackoverflow.com/questions/6038061/regular-expression-to-find-urls-within-a-string

Base:

stackoverflow.com

Regex:
(http(s)?:\/\/)|(\/.*){1}

Example in JavaScript:

function toBaseURL(fullURL){
    return fullURL.replace(/(http(s)?:\/\/)|(\/.*){1}/g, '');
}