JSFiddle - React, Tailwind, and code Playground

HTML

<iframe id="iframe-ad-1" src="//example.com"></iframe>
<iframe id="iframe-ad-2" src="//example.com"></iframe>
<div id="message"></div>

CSS

iframe {
    width: 500px;
    height: 150px;
}

JavaScript

var monitor = setInterval(function(){
    var elem = document.activeElement;
    if(elem && elem.tagName == 'IFRAME'){
				message.innerHTML = 'Clicked ' + elem.id;
        // clearInterval(monitor);
    } else {
        		message.innerHTML = '---';
    }

}, 500);