code: function (value, min, max) {
          min = min | 0;
          let length = ((value || '') + '').length;
          if (length < min) {
              return false;
          }
          if (max && length > max) {
              return false;
          }
          return true;
      }
docs: 长度区域
  @param  {[type]} min [description]
  @param  {[type]} max [description]
  @return {[type]}     [description]