判断是否已经引入js

//判断是否已经引入js
        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;
        }

if (!isInclude("swiper.js")) {
                    var oHead = document.getElementsByTagName('HEAD').item(0);
                    var oScript = document.createElement("script");
                    oScript.type = "text/javascript";
                    oScript.src = "js/swiper.js";
}