cross site iframe postMessage from child to parent

Question

I found this samplefrom 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

Answer 1

You need to set targetOrigin when using postMessage.

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

Then on the host page.

function addAnEventListener(obj,evt,func){
    if ('addEventListener' in obj){
        obj.addEventListener(evt,func, false);
    } else if ('attachEvent' in obj){//IE
        obj.attachEvent('on'+evt,func);
    }
}

function iFrameListener(event){
     secondPageValue = event.data;
}

var secondPageValue='';

addAnEventListener(window,'message',iFrameListener);

Answer 2

Check http://davidwalsh.name/window-iframe out. This is a perfect working example.

The parent object provides a reference to the main window from the child. So if I have an iFrame and console the parent within it, the console will read:

// Every two seconds....
setInterval(function() {
    // Send the message "Hello" to the parent window
    // ...if the domain is still "davidwalsh.name"
    parent.postMessage("Hello","http://davidwalsh.name");
}, 3000);

Since we now have hold of the window, we can postMessage to it:

// Create IE + others compatible event handler
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) {
  console.log('parent received message!:  ',e.data);
},false);

The directive above triggers the iFrame to send a message to the parent window every 3 seconds. No initial message from the main window needed!