helper.js

module.exports = exports = function resolve(url, base_url) {
    var doc      = document
        , old_base = doc.getElementsByTagName('base')[0]
        , old_href = old_base && old_base.href
        , doc_head = doc.head || doc.getElementsByTagName('head')[0]
        , our_base = old_base || doc_head.appendChild(doc.createElement('base'))
        , resolver = doc.createElement('a')
        , resolved_url
        ;
    our_base.href = base_url;
    resolver.href = url;
    resolved_url  = resolver.href; // browser magic at work here

    if (old_base) old_base.href = old_href;
    else doc_head.removeChild(our_base);
    return resolved_url;
};