[Moo] get the background-image url the Mootools way

[mmjaeger]

Hello
I was wondering whether there is a specific function to retrieve the
background-image url - I've the following function but maybe there's a
better way:

var url = el.getStyle('background-image');
url = _cleanupUrl(url);

_cleanupUrl: function(aUrl) {

           var regExp = /^url\("?(.*?)"?\)$/ig;
           var matches = regExp.exec(aUrl);

           if(matches == null || typeof matches[1] == "undefined")
              return null;

           return matches[1];
        },

thanks