code: function reduceStack(path, items, item) {
        var nextPath;
  
        if (item.handle && item.handle.stack) {
          nextPath = join(path, (item.path || helpers.unescapeRegex(item.regexp) || ''));
          return items.concat(item.handle.stack.reduce(reduceStack.bind(null, nextPath), []));
        }
  
        if (item.route) {
          nextPath = join(path, (item.route.path || ''));
          return items.concat(item.route.stack.reduce(reduceStack.bind(null, nextPath), []));
        }
  
        return items.concat({
          handle: item.handle,
          path: path
        });
      }
docs: Reducing the app's recursive stack