怎样动态地插入不会暴露给用户的JS文件

也是无心间看见的，之前想过这个问题，可是没多想，今天看到这段代码豁然开朗

(function() {
    var dynamicScript = document.createElement('script'); 
    dynamicScript.type = 'text/javascript'; 
    dynamicScript.async = true;
    dynamicScript.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.xxx.com/dynamicScript.js';
    var firstScript = document.getElementsByTagName('script')[0]; 
    s.parentNode.insertBefore(dynamicScript, firstScript);
})();