window.parent only works with iframes and window.opener works with separate windows.

On top of that, since I was trying to send a message to the parent window, but the new window was opened by the iframe IN that window.

So window.opener reached the iframe - then I had to actually send the message to its parent:

window.opener.parent.postMessage(etc, etc);

The following works for me in chrome, firefox, ie(didn't test more browsers)

assume 3 documents

1. (www.mydomain.com/parent.html)the page that contains the 'main'-document with the link
2. (bills.mydomain.com/child.html)the page that will be opened by the link
3. (www.mydomain.com/dispatcher.html)explained later

at first set the domain-property of all 3 documents to mydomain.com

<script>
document.domain="mydomain.com";
</script>

in parent.html create a hidden iframe with a name-property of e.g. "hiddenframe". Also create some function that may later receive a response.

parent.html should now look like this:

<script>
document.domain="mydomain.com";
function fx(msg)//receives the response
{
  alert(msg)
}
</script>
<iframe name="hiddenframe" style="display:none"></iframe>
<a href="http://bills.mydomain.com/child.html" target="_blank">click</a>

In child.html you'll now be able to load a document into the hidden iframe inside parent.html

<script>
document.domain="mydomain.com";
window.open('http://www.mydomain.com/dispatcher.html','hiddenframe');
</script>

(don't be confused in face of the use of window.open() here, there will not open a new window, the page will be loaded into the iframe in parent.html)

In dispatcher.html you now may call the function inside parent.html

<script>
document.domain="mydomain.com";
parent.fx('you just got some response');
</script>

When you only need to reload the parent.html it's a little bit easier.

Again set the document.domain-property in parent.html and child.html(you don't need the iframe in parent.html and the dispatcher.html)

In parent.html also set the name-property of the window, e.g.

<script>
  window.name="parentTab";
</script>

In child.html you now may access the parentTab-window(tab)

<script>
    document.domain="mydomain.com";
    window.open('http://www.mydomain.com/parent.html','parentTab');
</script>

...or simply use "parentTarget" as target-property of a link or form in child.html

It has worked now, earlier I was doing some syntax mistake. Here is the correct code for the same.

//parent Window
childWindow=window.open("http:/localhost/abcd.php","_blank","width=500,height=500");
childWindow.postMessage('message',"http://localhost:80/child.php");


//child Window
var newUrl='';
window.addEventListener(
 "message",
 function(e) { 

console.log(e.data);//your data is captured in e.data 
}, false);

The window.opener object is what you're looking for, used it from within your popup like so to call the a function of the parent window:

window.opener.yourFunc() 

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 key = e.message ? "message" : "data";
    var data = e[key];
    //run function//
},false);

Got it to work with the above in the parent page and the following in the child page -    

parent.postMessage("loadMyOrders","*");  //  `*` on any domain         

Code copied from here.