Hello,after last update on version Chrome 61, it is not possible to unload iframe with JS. I tried:
$('#iframe').attr('src', '');
$('#iframe').attr('src', 'about:blank');
$('#iframe').empty();
$('#iframe').contents().empty();
There is no problem with removing "src" attribute in iframe, as you can see on picture. But when you remove src, the old content from iframe will remain and it is not possible to clear it. Only thing, what I can do is load another page.
Check image from developer tools:
