title: what's the difference between setCount(prev => prev + 1) and setCount(count + 1)?
body: <p>I am reading an example of React hooks. I find they write</p>
  <pre><code>setCount(count + 1)
  </code></pre>
  <p>But I usually wrote like this</p>
  <pre><code>setCount(prev =&gt; prev + 1)
  </code></pre>
  <p>Is there any difference? Which one is better?</p>