動态加載 javascript

動态加載 javascript，可防止阻塞下載下傳。

function loadScript(url,callback){

//create a script tag

var script=document.createElement("script");

script.setAttribute("type","text/javascript");

if(script.readyState){ //IE support

script.onreadystatechange=function(){

if(script.readyState=="loaded" || script.readyState=="complete"){

if("function"==typeof callback) {

callback();

}

}

}

}else{ //FF, safari, chrome, and others

script["onload"]=function(){

if("function"==typeof callback) {

callback();

}

}

}

script.setAttribute("src",url);

document.getElementsByTagName("head")[0].appendChild(script);

} 

使用：

loadScript("http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js",

function(){

jQuery.extend({

out: function(s){document.write(s+"<br/>");}

});

$.out("Yes!!");

}

);