title: React hook only when props change?
body: <pre><code>useEffect(() =&gt; {
    // do something
  }, [stringProp]);
  </code></pre>
  <p><code>stringProp</code> is by default an empty string.</p>
  <p>When I change <code>stringProp</code> to <code>foobar</code> the effect runs.</p>
  <p>But,</p>
  <p>the <code>useEffect</code> also runs when the component first mounts, which I don't want.</p>
  <p>How to run an effect hook ONLY when props change?</p>