window.open safety

HTML

<a href="https://jsfiddle.net/kazu69/j339zf7k/" target="popup">window.opener</a>
    <script>
        var targets = document.querySelectorAll('a[target=_blank]');
        var openWindow = function(url) {
            var iframe, iframeDoc, script;
            iframe = document.createElement('iframe');
            iframe.style.display = 'none';
            document.body.appendChild(iframe);

            iframeDoc = iframe.contentDocument || iframe.contentWindow.document;

            script = iframeDoc.createElement('script');
            script.text = 'window.parent = null; window.top = null; window.frameElement = null; var child = window.open("' + url + '"); child.opener = null';

            iframeDoc.body.appendChild(script);
            newWin = iframe.contentWindow.child;

            document.body.removeChild(iframe);

            return newWin;
        }

        for(var i = 0; i < targets.length; i++) {
            targets[i].addEventListener('click', function(event) {
                var url = event.target.getAttribute('href');
                openWindow(url);
                event.preventDefault();
            });
        }
    </script>