PostMessage Receiver - How to retrieve the PostMessage

[chinoknot]

Hello, 
I need your help. I wrote about this thing two months ago, but without useful answer, now I need to complete this work. I understood better how it works, but I need the last thing. 

I try to explain my problem: I need to receive a "post" from another domain, but I can't understand how can I do this, because the sender send me a json and I need to get in my receiver. This is my code:

<script>
//create popup window
var domain = 'http://10.5.15.145';
var myPopup = window.open(domain + '/Apps/post/child_backup.php','myWindow



//periodical message sender
setTimeout(function(){
var message = JSON.stringify({action: "redirect", vendor_id :"45" });
console.log('blog.localending message: ' + message);
myPopup.postMessage(message,domain); //send the message and target URI
},1000);

//listen to holla back
window.addEventListener('message',function(event) {
if(event.origin !== 'http://10.5.15.145') return;
console.log('receivedponse: ',event.data);
},false);
</script>

Now the vendor_id is "45" for a test. They pass to me vendor_id: xxxx. 

how can I grab this value from the post?


Thank you in advance.