title: Vanilla JavaScript - How to check a option is selected in multiple select options?
body: <p>To check whether a <strong>checkbox</strong> is ticked we do this:</p>
  
  <pre><code>let isChecked = event.target.checked
  </code></pre>
  
  <p>What about a <strong>multiple select options</strong> like this below?</p>
  
  <pre><code>&lt;select name="books[]" multiple&gt;
    &lt;option value="A"&gt;A&lt;/option&gt;
    &lt;option value="B"&gt;B&lt;/option&gt;
    &lt;option value="C"&gt;C&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>How can we check if A is selected or when A is unselected when you select B?</p>