title: Equivalent of window.scrollY for a div
body: <p>What is the best way to detect how much a user scrolled Vertically in a <code>div</code> element using plain JS?
  These are snippets from my code:</p>
  
  <p>html</p>
  
  <pre><code>&lt;div id="blaaaa"&gt;
  &lt;!-- DIV CONTENT --&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>js</p>
  
  <pre><code>document.getElementById('blaaaa').addEventListener('scroll', this.handleScroll);
  
  handleScroll(e) {
    // I want to use an equivalent of window.scrollY but for a single div element
    var scrolled = window.scrollY;
    // ...
  },
  </code></pre>
  
  <p>How can I do that?</p>
  
  <p>I appreciate your answers. Happy Holidays!</p>