title: React Hooks : how to update props initialized by useEffect in parent component
body: <p>I'm new to React Hooks and I'm facing this problem :</p>
  
  <ul>
  <li>App component initializes a map from localStorage with useEffect</li>
  <li>it passes this map to child component Hello</li>
  </ul>
  
  <p>Then :</p>
  
  <ul>
  <li>child component copy this map in its own state and use it manage values editions.</li>
  </ul>
  
  <p>Problem is, as you can see in this <a href="https://stackblitz.com/edit/react-wdv5nc" rel="nofollow noreferrer">stackblitz</a> console log :</p>
  
  <pre><code>parent map: undefined --- child map: undefined // map is first pass empty to the child component
  parent map: world --- child map: undefined     // then it's populated by parent component effect but child state is not updated
  </code></pre>
  
  <p>How can I manage proper initialization of map values in child component? Do not hesitate to challenge the whole thing, I'm not sure to use effects properly here.</p>