JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container" data-room="room1">some content</div>
<button onclick="changeroom('room2');">
Change
</button>

JavaScript

function changeroom(room) { document.getElementById("container").dataset.room=room; }

new MutationObserver(() => {
      const lastroom = "room1"; 
      if (document.getElementById("container").dataset.room !== "room1") {
      console.log('changed room')
      }
     }).observe(document, {subtree: true, childList: true});