title: How to properly use componentWillUnmount() in ReactJs
body: <p>From the official tutorial:</p>
  
  <blockquote>
    <p><code>componentWillUnmount()</code> is invoked immediately before a component is unmounted and destroyed. Perform any necessary cleanup in this method, such as invalidating timers, canceling network requests, or cleaning up any DOM elements that were created in <code>componentDidMount</code></p>
  </blockquote>
  
  <p>I understood "invalidating timers". <code>fetch</code> can be aborted with <code>AbortController</code>. But I don't understand "cleaning up any DOM elements that were created in <code>componentDidMount</code>", can I see examples for that case?</p>