code: function guid() {
      function s4() {
          return Math.floor((1 + Math.random() + ((new Date()).getMilliseconds()/1000)) * 0x10000)
              .toString(16)
              .substring(1);
      }
      return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
          s4() + '-' + s4() + s4() + s4();
  }
docs: 取GUID