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;

    qs = qs.replace(/\+/g, ' ');
    var args = qs.split('&');
    
    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])
            : name;
        
        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);
}