Userscripts XDR wrapper

/* Requires _opera-xdr-engine.js to handle script-based requests in Opera*/
var xdr = {
        /* request ID, JSONP counter*/
        reqId : 0,
        req : {},
        /* Prevent caching*/
        prepareUrl : function(url){
            url = /\?/.test(url) ? url + "&" + seed : url + "?" + seed;
            return url;
        },
        /*
         *
         */
        xget : function(url, onDone){
            url = this.prepareUrl(url);
            if (window.opera && window.opera.defineMagicVariable){
                this.scriptTransport(url, onDone);
            } else if(chrome && chrome.extension) {
                this.xhrTransport(url, onDone);
            } else if (GM_xmlhttpRequest){
                this.GMTransport(url,onDone);
            } else {
                var currentReqId = this.reqId++;
                this.req[currentReqId].handleJSONP = onDone;

                this.JSONPTransport(url, "xdr.req["+currentReqId+"].handleJSONP");
                        }
        },

        /**
         * Make GET request via <script> transport.
         *
         */
        scriptTransport : function(url, onDone){
            var t = document.createElement("script");
            t.src = url;
            t._callback = onDone;
            document.body.appendChild(t);
        },

        // transport should be proxyed via background.html of the chrome
        // extension
        xhrTransport : function(url, onDone){
            chrome.extension.sendRequest({'action' : 'xget', 'url':url}, onDone);
        },
        /**
         * Make GET request via GM_xmlhttpRequest.
         *
         */
        GMTransport : function(url, onDone){
            setTimeout(function(){GM_xmlhttpRequest({
                method : "GET",
                url : url,
                onload : function(x) {
                    var o = x.responseText;
                    if (onDone) {
                        onDone(o);
                    }
                }
            });},0);

        },
        JSONPTransport : function(url, callbackName ){
            if (callbackName && typeof callbackName == "string"){
                url += "&callback="+callbackName;
            }
            var t = document.createElement("script");
            t.src = url;
            document.body.appendChild(t);
        }
    }