如何使用jquery动态加载js,css文件实现代码

$.extend({ 
includePath: '', 
include: function(file) { 
var files = typeof file == "string" ? [file]:file; 
for (var i = 0; i < files.length; i++) { 
var name = files[i].replace(/^\s|\s$/g, ""); 
var att = name.split('.'); 
var ext = att[att.length - 1].toLowerCase(); 
var isCSS = ext == "css"; 
var tag = isCSS ? "link" : "script"; 
var attr = isCSS ? " type='text/css' rel='stylesheet' " : " language='javascript' type='text/javascript' "; 
var link = (isCSS ? "href" : "src") + "='" + $.includePath + name + "'"; 
if ($(tag + "[" + link + "]").length == 0) document.write("<" + tag + attr + link + "></" + tag + ">"); 
} 
} 
}); 

//使用方法 
$.includePath = 'http://hi.baidu.com/javascript/'; 
$.include(['json2.js', 'jquery.tree.js', 'jquery.tree.css']);