title: Get the height of an children element
body: <p>Hello i will set the height for my div into state.</p>
  
  <p>i tried get the whole height by <code>get window.innerHeight</code>this worked fine but i cant access the children of my div, i also try <code>document.getElementById('masonryParent')</code> i get also the right result but how i can access the div bellow. Any suggestions?  </p>
  
  <pre><code> this.setState({
        width: window.innerWidth, height: window.innerHeight
      });
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/9LqxK.png" rel="noreferrer"><img src="https://i.stack.imgur.com/9LqxK.png" alt="enter image description here"></a></p>