code: function request(url, fn) {
      var method = 'GET';
  
      if ('string' == typeof fn) {
          method = url;
          url = fn;
          fn = arguments[2];
      }
  
      fn = fn || function () {
      };
  
      o.ajax({ type: method, url: url })
          .success(function (res) {
              res.error
                  ? error(res.error)
                  : fn(res);
          });
  }
docs: Request `url` and invoke `fn(res)`.
  
  @param {String} url
  @param {Function} fn