(function() {
   document.write("<div id=\"holder\"></div>");
   
   var script = document.createElement("script");
   script.type = "text/javascript";
   script.src = "asyncTest.js";
   script.id = "asyncTest";
   script.setAttribute("async", "async");
   
   var head = document.documentElement.firstChild;
   head.appendChild(script);
})();