title: What is the `$` 's meaning in this code?
body: <p>Here is partly code,I got confused about the <code>$</code> 's meaning.</p>
  
  <pre><code>function playSound(e) {
       const audio = document.querySelector('audio[data-key="${e.keyCode}"]');
       const key = document.querySelector('.key[data-key="${e.keyCode}"]');
       ...
  }
  </code></pre>
  
  <p>I know the first code will return the first element <code>&lt;audio&gt;</code> which has <code>data-key="..."</code> .But I don't understand the <code>$</code>'s function and how to find it.So is there a document to explain it or anything else can help me understand it?</p>