code: function chainCallback(cb, next) {
      var browser = this;
  
      return function queueWrapped() {
          try {
              if (cb) {cb.apply(browser, arguments);}
              next();
          } catch (e) {
              next(e);
          }
      };
  }
docs: catch any error and passes it to next. Once callback is called, next is called.  * cb: the callback to call * next: the next in chain method