title: Filter object of object of array properties by key javascript
body: <p>I have this objects i want to filter articles by news ,funny and sports</p>
  <pre><code>const articles = {
  article_1: {
   
  tags: ['news', 'funny']
  },
  article_2: {
  tags: ['sports', 'funny']
  }
  }
  </code></pre>
  <p>i want to filter to have result</p>
  <pre><code>const articlesByTag = groupArticlesByTag(articles);
  
  articlesByTag = {
  news: ['article 1'],
  funny: ['article 1', 'article 2'],
       
  sports: ['article 2']
  }
  </code></pre>