readystate, 异步

 EventUtil.addHandler(window, "load", function(){

            //create a new <script/> element.
            var script = document.createElement("script");
            EventUtil.addHandler(script, "readystatechange", function(event){
                event = EventUtil.getEvent(event);
                var target = EventUtil.getTarget(event);
                if (target.readyState == "loaded" || target.readyState == "complete"){
                    EventUtil.removeHandler(target, "readystatechange", arguments.callee);
                    alert("Script Loaded");
                }
            });
            script.src = "example.js";
            document.body.appendChild(script);

            //create a new <link/> element
            var link = document.createElement("link");
            link.type = "text/css";
            link.rel= "stylesheet";

            EventUtil.addHandler(link, "readystatechange", function(event){
                event = EventUtil.getEvent(event);
                var target = EventUtil.getTarget(event);
                if (target.readyState == "loaded" || target.readyState == "complete"){
                    EventUtil.removeHandler(target, "readystatechange", arguments.callee);
                    alert("CSS Loaded");
                }
            });
            link.href = "example.css";
            document.getElementsByTagName("head")[0].appendChild(link);

        });