JS如何判断是否已经引入某个css或是js？

http://bbs.csdn.net/topics/390541081

function isInclude(name){

    var js= /js$/i.test(name);

    var es=document.getElementsByTagName(js?'script':'link');

    for(var i=0;i<es.length;i++) 

    if(es[i][js?'src':'href'].indexOf(name)!=-1)return true;

    return false;

}

alert(isInclude("abc.js"));

alert(isInclude("efg.css"));