8 years later, many browsers (except for Internet Explorer) support the URL constructor (URL(url [, base])).
> new URL('../address', 'http://www.adress.com/more/evenmore/').href
"http://www.adress.com/more/address"
> new URL('../../address', 'http://www.adress.com/more/evenmore/').href
"http://www.adress.com/address"