How do you use window.postMessage across domains?
It seems like the point of window.postMessage is to allow safe communication between windows/frames hosted on different domains, but it doesn't actually seem to allow that in Chrome.
Here's the scenario:
- Embed an <iframe> (with a
srcon domain B*) in a page on domain A - The <iframe> ends up being mostly a <script> tag, at the end of which's execution...
- I call window.postMessage( some_data, page_on_A )
The <iframe> is most definitely in the context of domain B, and I've confirmed that the embedded javascript in that <iframe> executes properly and calls postMessage with the correct values.
I get this error message in Chrome:
Unable to post message to A. Recipient has origin B.
Here's the code that registers a message event listener in the page on A:
window.addEventListener(
"message",
function (event) {
// Do something
},
false);
I've also tried calling window.postMessage(some_data, '*'), but all that does is suppress the error.
Am I just missing the point here, is window.postMessage(...) not meant for this? Or am I just doing it horribly wrong?
*Mime-type text/html, which it must remain.
Answer
Here is an example that works on Chrome 5.0.375.125.
The page B (iframe content):
<html>
<head></head>
<body>
<script>
top.postMessage('hello', 'A');
</script>
</body>
</html>
Note the use of top.postMessage or parent.postMessage not window.postMessage here
The page A:
<html>
<head></head>
<body>
<iframe src="B"></iframe>
<script>
window.addEventListener( "message",
function (e) {
if(e.origin !== 'B'){ return; }
alert(e.data);
},
false);
</script>
</body>
</html>
A and B must be something like http://domain.com
EDIT:
From another question, it looks the domains(A and B here) must have a / for the postMessage to work properly.