[whatwg] Should events be paused on detached iframes?

Tue Aug 24 15:27:49 PDT 2010

Indeed, in WebKit you normally see #1 (iframe unloads). We have added the
ability to move 'live' iframe, as Adam mentions, potentially across
documents, while keeping it completely alive, with XHRs loading, events
firing etc (aka 'magic iframe' feature). One would need to use adoptNode()
API to do that, something like:

var iframe = document.getElementById("test");
other_document.adoptNode(iframe);
other_document.getElementById("newParent").attachChild(iframe);

WebKit has a bug (https://bugs.webkit.org/show_bug.cgi?id=13574) to enable
moving iframes w/o reloading. FF has a bug on that as well (
https://bugzilla.mozilla.org/show_bug.cgi?id=254144) but it's hard to say
when exactly those will be fixed. I hope to fix WebKit issue at some point.

While discussing 'magic iframe', Ian Hickson pointed out that nothing in the
spec actually mandates discarding the live document inside iframe simply
because it's iframe element is connected/disconnected to DOM of the parent
document. Here is a note from the HTML5 spec about that:
Removing<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#remove-an-element-from-a-document>
 an iframe<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#the-iframe-element>
from
a Document<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#document>
does
not cause its browsing
context<http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context>
to
be discarded. Indeed, an
iframe<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#the-iframe-element>
's browsing context<http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context>
can
survive its original parent
Document<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#document>
if
its iframe<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#the-iframe-element>
is
moved to another
Document<http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#document>
.

So it seems the right behavior is to keep the content alive. It's not clear
why the events would not fire during DOM operations though. Perhaps they
should, since nothing is changing from the perspective of the document
loaded into iframe - for example, XHR probably should continue loading
content if it was doing so before iframe was disconnected from its parent
node. Doing some suspension (as for example is done when a page goes into
back-forward cache?) would be way more complex mechanism to have, with
necessary events on pause/unpause so the live document could re-start async
operations correctly.

Dmitry

On Tue, Aug 24, 2010 at 1:38 PM, Adam Barth <w3c at adambarth.com> wrote:

> This seems related to the "magic iframe" concept that was recently
> added in WebKit.  Basically, magic iframe lets you move an iframe from
> one document to another without blowing away the JavaScript/DOM state
> of the iframe.  The way this works is that the iframe remains "alive"
> until the browser returns to the main event loop.  If a living iframe
> gets added to a document, then it keeps all it's state.  This feature
> is useful for sites like Gmail that have chat windows that can be
> opened from the main document.  If the user closes the main document,
> the chat windows can adopt some iframe that keeps the proper state.
>
> Adam
>
>
> On Tue, Aug 24, 2010 at 1:30 PM, Ben Lerner <blerner at cs.washington.edu>
> wrote:
> >  There seems to be a bit of disagreement among browsers about how event
> > loops and iframes interact when an iframe is removed and then reinserted
> > into its parent document.  Consider the following two documents: the
> parent
> > document has a button that removes or reattaches an iframe to the
> document,
> > while the second simply sets an interval to update the page content.
> >
> > Page1.html:
> > <!DOCTYPE HTML>
> > <html>
> > <body>
> > <p><button onclick="toggleInDoc();">Show/hide</button></p>
> > <iframe id="test" src="page2.html"></iframe>
> > <script>
> >    var test = document.getElementById("test");
> >    function toggleInDoc() {
> >      if (test.parentNode == null)
> >        document.body.appendChild(test);
> >      else
> >        document.body.removeChild(test);
> >    }
> > </script>
> > </body>
> > </html>
> >
> >
> > Page2.html:
> > <!DOCTYPE HTML>
> > <html>
> > <body>
> > <p id="test"></p>
> > <script>
> >    window.setInterval(function() {
> document.getElementById("test").innerHTML
> > += "."; }, 500);
> > </script>
> > </body>
> > </html>
> >
> >
> > Assume the user waits until the interval has fired several times, then
> > presses the button, waits a while, and presses it again.  There are three
> > possible outcomes:
> > 1. When the iframe is reattached, the inner page reloads.  This seems to
> go
> > beyond the wording of the spec, which says only "When an iframe element
> is
> > first inserted into a document, the user agent must create a nested
> browsing
> > context, and then process the iframe attributes for the first time."
>  (This
> > isn't the first time the iframe is inserted into the document, so we
> > shouldn't process the iframe attributes again.)
> >
> > 2. The interval (and presumably, all events) in the iframe is paused
> while
> > it's been detached (since the document is no longer fully active, but it
> > also has not been discarded because of the global reference to its
> container
> > element).
> >
> > 3. The interval (and presumably, all events) continues to fire while it's
> > been detached, and the content of page2 will have changed while it's been
> > detached from page1.
> >
> > So far, Chrome 6, Opera 10.6 and Firefox 3.6 follow #1, and IE 8 follows
> #3.
> >  My reading of the "fully active" clause of the spec leads me to expect
> #2.
> >  Which of these behaviors is the desired one?  And/or, would it be
> desirable
> > to permit authors to specify which behavior they intend?
> >
> > Thanks,
> > ~ben
> >
>
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