title: Blinking element Javascript
body: <p>This is an html div element:</p>
  <pre><code>&lt;div id=&quot;elem&quot;&gt;A blinking element&lt;/div&gt;
  </code></pre>
  <p>This is the Javascript code:</p>
  <pre><code>let elem = document.getElementById(&quot;elem&quot;);
  setInterval(() =&gt; elem.hidden = !elem.hidden, 1000);
  </code></pre>
  <p>The code is to make the element blink after a second, why is the function in <code>setInterval</code> <code>elem.hidden = !elem.hidden</code> what does it mean, I mean the function</p>