article favorite/unfavorite

//...

// favorite article
router.post('/:article/favorite', auth.required, function(req, res, next) {
  // extract id from posted article
  var articleId = req.article._id;

  // find posted user, favorite the article, update favorite count, and return article
  User.findById(req.payload.id).then(function(user){
    if (!user) { return res.sendStatus(401); }

    return user.favorite(articleId).then(function(){
      return req.article.updateFavoriteCount().then(function(article){
        return res.json({article: article.toJSONFor(user)});
      });
    });
  }).catch(next);
});

// unfavorite. Ditto favorite method, but using user.unfavorite
router.delete('/:article/favorite', auth.required, function(req, res, next) {
  var articleId = req.article._id;

  User.findById(req.payload.id).then(function (user){
    if (!user) { return res.sendStatus(401); }

    return user.unfavorite(articleId).then(function(){
      return req.article.updateFavoriteCount().then(function(article){
        return res.json({article: article.toJSONFor(user)});
      });
    });
  }).catch(next);
});

module.exports = router;