title: Anonymous "likes/reactions" using Firebase
body: <p>Question from junior Padawan to real Jedy.</p>
  <p>I'm developing a website for a designer portfolio. Without any registration and backend. I'm using Firebase instead. I need to add a feature to collect &quot;likes&quot; (reactions) from anonymous users on works/posts.</p>
  <p>Firebase RTDB structure:</p>
  <pre><code>+artworks:
    +someArtWorkID1: 
       name: &quot;lorem ipsum&quot;
       description: &quot;lorem ipsum&quot;
       date: &quot;01.01.1970&quot;
       src: &quot;here should be url to picture&quot;
       **likes**: (?)
  </code></pre>
  <p>Idk how to implement it. Should it be a simple number or array of UIDs (anonymous user ID)?</p>
  <p>Or another structure:</p>
  <pre><code> +artworks...
   +likes:
     +idOfArtwork:
       uid: true,
       uid2: true
       ..........
  </code></pre>
  <p>But in that case, how can I calculate the sum of &quot;likes&quot; for specific post/artwork?</p>
  <p>Also, I am new to Firebase and haven't any ideas how to write rules for it. In order for the anonymous user could add/delete only his UID in the likes array. Or should I use another solution for this task? Help me please)</p>