javascript实现动态导入js与css等静态资源文件的方法

/** * 动态导入静态资源文件js/css */var $import = function(){  return function(rId, res, callback){    if(res && 'string' == typeof res){      if(rId){        if($($('#' + rId), $('head')).length>0){          return;        }      }      //加载资源文件      var sType = res.substring(res.lastIndexOf('.') + 1);      // 支持js/css      if(sType && ('js' == sType || 'css' == sType)){        var isScript = (sType == 'js');        var tag = isScript ? 'script' : 'link';        var head = document.getElementsByTagName('head')[0];        // 创建节点        var linkScript = document.createElement(tag);        linkScript.type = isScript ? 'text/javascript' : 'text/css';        linkScript.charset = 'UTF-8';        if(!isScript){          linkScript.rel = 'stylesheet';        }        isScript ? linkScript.src = res : linkScript.href = res;        if(callback && 'function' == typeof callback){          if (linkScript.addEventListener){            linkScript.addEventListener('load', function(){              callback.call();            }, false);          } else if (linkScript.attachEvent) {            linkScript.attachEvent('onreadystatechange', function(){              var target = window.event.srcElement;              if (target.readyState == 'complete') {                callback.call();              }            });          }        }        head.appendChild(linkScript);      }    }  };}();