I'm trying to make a trivial postMessage example work...
Remove any one of these conditions, and things work fine :-)
But as far as I can tell, between-window postMessage only appears to work in IE10 when both windows share an origin. (Well, in fact -- and weirdly -- the behavior is slightly more permissive than that: two different origins that share a host seem to work, too).
(Note: This question touches on the issues, but its answer is about IE8 and IE9 -- not 10)
More details + example...
<!DOCTYPE html>
<html>
<script>
window.addEventListener("message", function(e){
console.log("Received message: ", e);
}, false);
</script>
<button onclick="window.open('http://jsbin.com/ameguj/1');">
Open new window
</button>
</html>
<!DOCTYPE html>
<html>
<script>
window.opener.postMessage("Ahoy!", "*");
</script>
</html>
This works at: http://jsbin.com/ahuzir/1 -- because both pages are hosted at the same origin (jsbin.com). But move the second page anywhere else, and it fails in IE10.
I was mistaken when I originally posted this answer: it doesn't actually work in IE10. Apparently people have found this useful for other reasons so I'm leaving it up for posterity. Original answer below:
Worth noting: the link in that answer you linked to states that postMessage isn't cross origin for separate windows in IE8 and IE9 -- however, it was also written in 2009, before IE10 came around. So I wouldn't take that as an indication that it's fixed in IE10.
As for postMessage itself, http://caniuse.com/#feat=x-doc-messaging notably indicates that it's still broken in IE10, which seems to match up with your demo. The caniuse page links to this article, which contains a very relevant quote:
Internet Explorer 8+ partially supports cross-document messaging: it currently works with iframes, but not new windows. Internet Explorer 10, however, will support MessageChannel. Firefox currently supports cross-document messaging, but not MessageChannel.
So your best bet is probably to have a MessageChannel based codepath, and fallback to postMessage if that doesn't exist. It won't get you IE8/IE9 support, but at least it'll work with IE10.
Docs on MessageChannel: http://msdn.microsoft.com/en-us/library/windows/apps/hh441303.aspx