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[whatwg] Inter-window communication beyond window.postMessage()

From: Jeremy Orlow <jorlow@chromium.org>
Date: Mon, 14 Sep 2009 17:57:04 -0700
Message-ID: <5dd9e5c50909141757i2b3948d8w880177709e4f3cc4@mail.gmail.com>
On Mon, Sep 14, 2009 at 3:06 PM, Ian Hickson <ian at hixie.ch> wrote:

> On Mon, 14 Sep 2009, Sidney San Mart?n wrote:
> >
> > The cross-document messaging API solves a lot of problems and is overall
> > an Awesome Thing, but requiring a reference to the target window is
> > hugely limiting. When a a window wants to talk to another window and
> > didn't create it, there are basically three options:
> >
> > 1. window.open with a window name argument, which is a hack because the
> target
> > window has to reload.
> > 2. Comet, which is a horrible hack because a trip to the server is
> required.
> > 3. LocalStorage and storage events, which wasn't designed for anything
> > remotely like this.
>
> 4. Open a SharedWorker and send a MessagePort to the other window.
>
>
> > Unless there's a reason to prevent free communication between windows,
> > there must be a better solution. I can think of a couple of
> > possibilities. The most obvious one would be an API similar to
> > postMessage that allows broadcasting of messages to all windows, windows
> > by name, and windows by domain. Another one (which I haven't developed
> > very far) would be to stick with window.postMessage but provide an API
> > to ask for windows. So, I could say, "Can I please have a reference to
> > the window named 'x'", or, "...to windows at 'example.com'", or, "...to
> > any window who'll give me one". Each window would obviously have to opt
> > into this.
> >
> > What do you all think?
>
> How do you know there's a Window to get a hold of if you don't have a hold
> of it already?
>
> The main reason for Window.postMessage() is communication with iframes
> (gadgets), not with other top-level browsing contexts. What's the use case
> for the latter?
>

I assume the use case for this is similar with the use case for storage
events which essentially is a broadcast mechanism that's specific to just
DOM storage.  So if, for example, you wanted to tell your other windows
"hey!  I changed the cookie" then you could do it with a message.  This
seems much better than, for example polling.

This could also be useful if you wanted to say "hey, I just navigated to
gmail.com.  Do any of you already have the inbox and chat contacts loaded
up?".  I suppose there's not much advantage to doing it like this over
shared workers since either way you're passing messages, but I also don't
see any major downsides to allowing broadcasts.
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