<script>  iframe.onload = function(){// we can get the reference to the inner windowletiframeWindow=iframe.contentWindow;// OKtry{// ...but not to the document inside itlet doc=iframe.contentDocument;// ERROR // 🟢}catch(e){alert(e);// Security Error (another origin)}// also we can't READ the URL of the page in iframetry{// Can't read URL from the Location objectlethref=iframe.contentWindow.location.href;// ERROR}catch(e){alert(e);// Security Error}// ...we can WRITE into location (and thus load something else into the iframe)!iframe.contentWindow.location='/';// OKiframe.onload=null;// clear the handler, not to run it after the location change};</script>