JSFiddle - React, Tailwind, and code Playground

HTML

<article>
  <p>
    Content goes here...
  </p>
  <script type="placeholder/ads" data-ad-id="123"></script>
</article>
<footer>
  <p>
    More content goes here...
  </p>
  <script type="placeholder/ads" data-ad-id="456"></script>
</footer>

JavaScript

var placeholders = document.querySelectorAll('script[type="placeholder/ads"]');

for (var i=0; i<placeholders.length; i++) {
  var ad = placeholders[i];
  
  var el = document.createElement("div");
  
  el.innerHTML = "Ad # " + ad.dataset.adId;
  
	ad.parentNode.replaceChild(el, ad)
}