JSFiddle - React, Tailwind, and code Playground

HTML

<iframe src="http://www.google.com/" onload="error_iframe(this);"></iframe>

<iframe src="http://www.w3schools.com/" onload="error_iframe(this);"></iframe>

JavaScript

function error_iframe(iframe){
	try{
		var win=iframe.contentWindow;
		win.closed && error_function(iframe);
	}catch(e){
		error_function(iframe);
	}
};

function error_function(e){
    alert('error: '+e.src);
}