cross site iframe postMessage from child to parent

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Javascript

HTML

jQuery

IFrame

Hello everyone -
I found this sample from SO while browsing for my problem, but I want to know exactly how to use it in my scenario. I have an iframe which is from another domain, and I want to detect when the iframe url is changed from one to another page in that other domain. So, what I was thinking is to have something like this when the 2nd page in the iframe is opened:

<script type="text/javascript">
    $(document).ready(function() {
parent.postMessage("Second Page");
}
</script>

That's all I need, I just need to receive message that the iframe has different url. Now on the parent page, I'll might have something like this:

<script type="text/javascript">
    $(document).ready(function() {
        $('#frame').load(function () {
            var eventMethod = window.addEventListener ? "addEventListener" : "attachEvent";
var eventer = window[eventMethod];
var messageEvent = eventMethod == "attachEvent" ? "onmessage" : "message";

// Listen to message from child window
eventer(messageEvent,function(e) {
 var secondPageValue = // I want to get the value from the child page here, how can I do that?
},false);
        });
    });
</script>

I'm trying to use this postMessage option for first time, so every advice will be greatly appreciated. Also, do I need to include some JS libraries such as jquery on child side to make this work?

Thanks in advance, Laziale