title: React: set focus on componentDidMount, how to do it with hooks?
body: <p>In React, with classes I can set the focus to an input when the component loads, something like this:</p>
  
  <pre><code>class Foo extends React.Component {
      txt1 = null;
  
      componentDidMount() {
          this.txt1.focus();
      }
  
      render() {
          return (
              &lt;input type="text"
                  ref={e =&gt; this.txt1 = e}/&gt;
          );
      }
  }
  </code></pre>
  
  <p>I'm trying to rewrite this component using the new <a href="https://reactjs.org/docs/hooks-intro.html" rel="noreferrer">hooks proposal</a>.</p>
  
  <p>I suppose I should use <a href="https://reactjs.org/docs/hooks-effect.html" rel="noreferrer"><code>useEffect</code></a> instead of <code>componentDidMount</code>, but how can I rewrite the focus logic?</p>