function loadScript(url, callback){
var script = document.createElement("script")
script.type = "text/javascript";
if (script.readyState){ //IE浏览器
script.onreadystatechange = function(){
if (script.readyState == "loaded" ||
script.readyState == "complete"){
script.onreadystatechange = null;
callback();
}
};
} else { //其他浏览器: Firefox, Safari, Chrome, and Opera
script.onload = function(){
callback();
};
}
script.src = url;
document.body.appendChild(script);
}