javascript实现js脚本的的异步加载，和图片的异步加载稍有不同，script的异步加载需要借助dom，因此有了局限性
<html>
<head>
<meta charset="utf-8" />
<title>Javascript</title>
<meta http-equiv="X-UA-Compatible" content="IE=7">
</head>
<body>
<script type="text/javascript" charset="utf-8">
function loadScript(url,callback)
{
var script = document.createElement(‘script‘);
if(!!document.setAttribute)
{
script.setAttribute(‘type‘,‘text/javascript‘);
script.setAttribute(‘charset‘,‘utf-8‘);
script.setAttribute(‘language‘,‘javascript‘);
}else{
script[‘type‘] =‘text/javascript‘;
script[‘charset‘] = ‘utf-8‘;
script[‘language‘] = ‘javascript‘;
}
if (!!script.readyState)
{
script.onreadystatechange = function()
{
if (script.readyState == "loaded" ||script.readyState == "complete")
{
script.onreadystatechange = null;
callback(script);
}
};
}else{
script.onload = function()
{
script.onload = null;
callback(script);
}
}
script[‘src‘] = url;
document.head.appendChild(script);
}
loadScript(‘https://fbstatic-a.akamaihd.net/rsrc.php/v2/yv/r/wgFc3t0g5gk.js‘,function(script){
console.log(script);
});
</script>
</body>
</html>
原文：http://my.oschina.net/ososchina/blog/345671