动态加载JS文件3种方式整理

document.writeln("<script src=\"http://lib.sinaapp.com/js/jquery/1.6/jquery.min.js\"></script>");

$.getScript('test.js',function(){
 alert('done');
});

function loadJs(url,callback){
 var script=document.createElement('script');
 script.type="text/javascript";
 if(typeof(callback)!="undefined"){
 if(script.readyState){
 script.onreadystatechange=function(){
  if(script.readyState == "loaded" || script.readyState == "complete"){
  script.onreadystatechange=null;
  callback();
  }
 }
 }else{
 script.onload=function(){
  callback();
 }
 }
 }
 script.src=url;
 document.body.appendChild(script);
 }
 loadJs("test.js",function(){
 alert('done');
 });