Shadow DOM

Drag this link to the Bookmarks Bar of your browser.

Check for Shadow DOM element

If you can't drag the link, copy the code below (or click this link) and bookmark it in the traditional way.

javascript:(function(){let e=document.querySelectorAll('*'),t=0;e.forEach(e=>{e.shadowRoot&&t++}),alert('This page contains '+t+' Shadow DOM elements.')})()

You'll see an alert like this:

See this Slack discussion about Shadow DOM.