MutationObserver class changes : <p>I am using <code>MutationObserver</code> to detect when a specific class has been added to an element. </p>

<pre><code>const observer = new MutationObserver((mutations) =&gt; { 
    mutations.forEach((mutation) =&gt; {
      const el = mutation.target;
      if ((!mutation.oldValue || !mutation.oldValue.match(/\bis-busy\b/)) 
        &amp;&amp; mutation.target.classList 
        &amp;&amp; mutation.target.classList.contains('is-busy')){
        alert('is-busy class added');
      }
    });
 });

observer.observe(document.querySelector('div'), { 
  attributes: true, 
  attributeOldValue: true, 
  attributeFilter: ['class'] 
});
</code></pre>

<p>My question is: <strong>Is there a better way to verify that this is a newly added class?</strong> Currently I am using regex to check that the class didn't exist previously and <code>classList</code> to check that the class exists now. Seems messy</p>

<p><a href="https://jsfiddle.net/s53o8dLe/12/" rel="noreferrer">Fiddle</a></p>
