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.readState ==
"complete"){
script.onreadystatechange = null;
callback();
}
}
}else{
script.onload = function(){
callback();
}
}
script.src = url;
document.getElementsByTagName("head")[0].appendChild(script);
}
原文：http://www.cnblogs.com/weibozeng/p/3527520.html