title: How to add a favorite item to a newly created list
body: <p>Would like to know, how to get a favorited item (in this case Elements A till C) to appear in only one specific, newly created list (which can be created by a user).</p>
  <p>For now, when I favorite an element, I get to see it in every of my newly created lists. Below is an example (sorry for the missing styling, used only <code>&lt;br /&gt;</code>):</p>
  <p><a href="https://i.stack.imgur.com/RtGE0.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RtGE0.jpg" alt="Web-app with 2 newly created lists and added Elements" /></a></p>
  <p>I assume, that it can be done with lists id (similar to how I delete the lists or favorites), but need a better understanding of it.
  Also I got a warning inside Chrome, that the child elements have no key value. I tried to add <code>shortId</code> inside .map in <code>&lt;li&gt;</code> (like <code>&lt;li key={shortid.generate()}&gt;</code>, but am afraid, that my solution is not an optimal one and it should be placed somewhere else (just where?)).</p>
  <p>Here is my CodeSandbox <a href="https://codesandbox.io/s/playing-with-creating-lists-m94h9?file=/src/components/App.jsx" rel="nofollow noreferrer">LINK</a></p>
  <p>Any help is welcome.</p>