When the iframe fails to load due to a 404 error or any other error, the 'onerror' event will be triggered, alloing you to handle the situation accordingly.
<!DOCTYPE html> <html> <head> <title>IFrame Error Detection</title> </head> <body> <iframe src="nonexistent-page.html" id="myIframe" width="400" height="300"></iframe> <script> const iframe = document.getElementById('myIframe'); iframe.onerror = function () { console.log('Error loading iframe content.'); // Add your error handling code here, such as displaying a message to the user or taking other actions. }; </script> </body> </html>