docs: function loadCSS(href, callback, attrs, timeout, fail, complete) {
      if ($.isObject(href)) {
          callback = href.callback;
          attrs = href.attrs;
          timeout = href.timeout;
          fail = href.fail;
          complete = href.complete;
          href = href.href;
          return loadCSS(href, callback, attrs, timeout, fail, complete);
      }
      var link = document.createElement('link');
      var done = false;
      
  
      timeout = $.isNumber(timeout) ? timeout : defaultConfig.timeout;
  
      var url = getPath(href);
      href = link.href = url[0];
      link.rel = 'stylesheet';
      link.type = 'text/css';
  
      
      if ($.isObject(attrs)) {
          for (var i in attrs) {
              link.setAttribute(i, attrs[i]);
          }
      }
      //弱化css 错误处理，只有callback的时候才处理
      if($.isFunction(callback)){
          complete = $.isFunction(complete) ? complete : emptyFn;
          var cb,err;
          cb = function() {
              if (!done) {
                  done = true;
                  link.onload = link.onerror = link.onreadystatechange = null;
                  mapLoaded[href] = 'loaded';
                  $.isFunction(callback) && callback();
                  complete('load');
              }
          }
          if($.isFunction(fail)){
              err = function() {
                  if (!done) {
                      done = true;
                      link.onload = link.onerror = link.onreadystatechange = null;
                      mapLoaded[href] = 'error';
                      fail();
                      complete('error');
                  }
              }
          }
  
          cssCallback(link, cb, err);
          if (timeout) {
              setTimeout(function() {
                  if (!done) {
                      done = true;
                      mapLoaded[href] = 'timeout';
                      complete('timeout');
                  }
              }, timeout);
          }
      }
      
      mapLoaded[href] = 'pending';
      head.insertBefore(link, base);
      return _;
  }