Treehouse

window.postMessage Tip: Child-To-Parent Communication

By on  

I wrote a super epic post a few months back about the window.postMessage API that's sweeping the nation.  window.postMessage allows you to send messages not only across frames (regular frame or iframe) but also across domains.  My post showed interaction from parent to child and back to the parent, but didn't detail passing messages from a child to a parent without the parent initializing the conversation.  Let me show you how you can initialize that conversation from child to parent

window.postmessage

The JavaScript

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");
},1000);

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!

ydkjs-2.png

Recent Features

Incredible Demos

  • Create a Simple Dojo Accordion

    Let's be honest:  even though we all giggle about how cheap of a thrill JavaScript accordions have become on the web, they remain an effective, useful widget.  Lots of content, small amount of space.  Dojo's Dijit library provides an incredibly simply method by which you can...

  • Duplicate the jQuery Homepage Tooltips Using Dojo

    The jQuery homepage has a pretty suave tooltip-like effect as seen below: Here's how to accomplish this same effect using Dojo. The XHTML The above HTML was taken directly from the jQuery homepage -- no changes. The CSS The above CSS has been slightly modified to match the CSS rules already...

Discussion

  1. kevin

    Great article, It worked great on iFrame resizing…WOO HOO! after many failed posts and other methods, this one was so simple.

  2. Stanton W. Jones

    Hey,

    So I’ve scoured the usual forums for a solution to cross-domain iframe communication, and nothing has worked. Not copy/paste, not my own code, not even on the same domain. A lot can change in a year ( haven’t found an article published in 2012 that tells me how to implement this) but I am in deep need of a sanity check.

    –SWJ

  3. Hi,
    My outside of iframe facny box is not working in chrome.so how to solve that problem.

  4. Baker

    Hi David,

    Thanks man. I’ve been looking for a solution for iframe resizing across domains since yesterday. I’ve finally found it.

    Really appreciate it.
    Cheers

  5. karstrasse

    Hi,

    I am getting an error:

    Uncaught TypeError: Object # has no method 'postMessage' even though I am able to get the iframe and its details.

  6. Hey, it looks and works great but on IE, action passed received is undefined.

    parent.postMessage({'action':'RESIZE', 'height':height}, '*');
    

    but here this Action: RESIZE is undefined in postmessage on IE

  7. Abhi

    How do i post the message from iframe which contains https page to a parent page which is http? Even the domains are different? Any idea?

  8. coderone

    It just works :)

  9. Gopinath

    Some browsers supports only ‘string’ message than any other objects(Eg:JSON)

  10. john

    Could you do it like this also?

    //the iframe code
    setInterval(function() {
    	parent.postMessage("Hello","http://davidwalsh.name");
    },1000);
    
    //The parent code
    $(window).on('message', function(e){
      console.log('parent received message!:  ',e.data);
    });
    
  11. Pandi

    Hi
    Can postmessage work for HTTPSHTTPS communications?

  12. Mariano

    Thanks, it was very useful and simple.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!