object > array > forEach object > array > push variable does not save after closing out of forEach loop

Question

I'm thinking it has something to do with the way javascript handles parent/child mutating... but I"m not sure.

The code:

router.get('/:id/articles', authenticate, async (req, res, next) => {
  try {
    let user = await db.getUserIdName(req.params.id);

    if (user) {
      articles = await db.getUserArticles(req.params.id);
      user.articles = articles;

      // select categories.id from `articles_categories_relationship` join `categories` on `articles_categories_relationship`.`article_id` = `categories`.`id` where `articles_categories_relationship`.`category_id` = '1'

      let finalUser = Object.assign({}, user);

      user.articles.forEach(async (article, index) => {
        finalUser.articles[index].categories = [];
        const newCategories = await dbArticles.getCategoriesByArticleId(
          article.id
        );

        newCategories.forEach(async category => {
          await finalUser.articles[index].categories.push(category.id);
        });
        console.log(newCategories);
        console.log(finalUser.articles[index].categories);
      });
      console.log(finalUser);
      // console.log(user.articles[0]);

      res.status(200).json(finalUser);
    } else {
      next({ code: 400 });
    }
  } catch (err) {
    next(err);
  }
});

Here is what the console.log()'s output is... Note: see categories

{ id: 1,
  display_name: 'RandomBlogger',
  articles:
   [ { id: 1,
       user_id: 1,
       cover_page: 'https://coverpage1.com/',
       title: 'Hello World',
       link: 'https://helloworld.com/',
       categories: [] },
     { id: 2,
       user_id: 1,
       cover_page: 'https://i.imgur.com/zbg9mtf.png',
       title: 'Lambda Strikes Down Students With New Build Week',
       link: '',
       categories: [] },
     { id: 3,
       user_id: 1,
       cover_page: '',
       title: 'Deadlines?-?Bad reason for bad code.',
       link: 'https://medium.com/mindorks/deadlines-bad-reason-for-bad-code-d3d5fe22f3ff',
       categories: [] } ] }
::1 - GET /users/1/articles HTTP/1.1 200 526 - 7.632 ms
[ { id: 1 }, { id: 3 } ]
[ 1, 3 ]
[ { id: 2 } ]
[ 2 ]
[ { id: 1 } ]
[ 1 ]

Here is what I expect from the console.log()'s output... Note: see categories

{ id: 1,
  display_name: 'RandomBlogger',
  articles:
   [ { id: 1,
       user_id: 1,
       cover_page: 'https://coverpage1.com/',
       title: 'Hello World',
       link: 'https://helloworld.com/',
       categories: [ 1, 3 ] },
     { id: 2,
       user_id: 1,
       cover_page: 'https://i.imgur.com/zbg9mtf.png',
       title: 'Lambda Strikes Down Students With New Build Week',
       link: '',
       categories: [ 2 ] },
     { id: 3,
       user_id: 1,
       cover_page: '',
       title: 'Deadlines?-?Bad reason for bad code.',
       link: 'https://medium.com/mindorks/deadlines-bad-reason-for-bad-code-d3d5fe22f3ff',
       categories: [ 1 ] } ] }
::1 - GET /users/1/articles HTTP/1.1 200 526 - 7.632 ms
[ { id: 1 }, { id: 3 } ]
[ 1, 3 ]
[ { id: 2 } ]
[ 2 ]
[ { id: 1 } ]
[ 1 ]

If anyone could explain to me why these changes are not being saved after it exits the parent forEach loop, I would be very grateful