function Querystring(qs)
{ // optionally pass a querystring to parse
        this.params = {};

        if (qs == null) qs = location.search.substring(1, location.search.length);
        if (qs.length == 0) return;

        // Turn <plus> back to <space>
        // See: http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4.1
        qs = qs.replace(/\+/g, ' ');
        var args = qs.split('&'); // parse out name/value pairs separated via &

        // split out each name=value pair
        for (var i = 0; i < args.length; i++) {
            var pair = args[i].split('=');
            var name = decodeURIComponent(pair[0]);

            var value = (pair.length==2) ? decodeURIComponent(pair[1]) : "";

            this.params[name] = value;
        }
}

Querystring.prototype.get = function(key, default_)
{
        var value = this.params[key];
        return (value != null) ? value : default_;
}

Querystring.prototype.contains = function(key)
{
        var value = this.params[key];
        return (value != null);
}