function loadScript(url, callback){
 
 var script = document.createElement("script")
 script.type = "text/javascript";
 
 if (script.readyState){  //IE
    script.onreadystatechange = function(){
     if (script.readyState == "loaded" ||
         script.readyState == "complete"){
           script.onreadystatechange = null;
           callback();
        }
     };
 } else {  //Others
   script.onload = function(){
     callback();
   };
 }
 
 script.src = url;
 document.getElementsByTagName("head")[0].appendChild(script);
}