Porthole by ternarylabs

Porthole is a small Javascript library that makes it safe and easy to communicate with cross domain iFrames. Porthole relies on hidden iFrames (later referred to a as proxy) to exchange information. The caller sets a url fragment with the message to pass. The proxy by virtue of being served from the same origin as the callee, invokes a callback method with an event object that contains the message read from the url fragment. The message signaling mechanism is based on a resize event.

Learn more about Porthole.

Design Goals

Porthole is designed with these goals in mind:

Small, only 5KB
Pure Javascript, does not rely on a framework
Work cross browser
Forward compatible, will use built-in postMessage for modern browsers

Usage

Include the Javascript.

<script type="text/javascript" src="porthole.min.js"></script>

Create your content iFrame. This is where the guest content lives. Make sure to give it a name.

<iframe id="guestFrame" name="guestFrame" src="http://other-domain.com/">
</iframe>

Define an event handler if you want to receive messages.

function onMessage(messageEvent) {  
    /*
   messageEvent.origin: Protocol and domain origin of the message
   messageEvent.data: Message itself
   messageEvent.source: Window proxy object, useful to post a response 
   */
}

Create a window proxy object on the main page.

var windowProxy;
window.onload=function(){ 
    // Create a proxy window to send to and receive 
    // messages from the iFrame
    windowProxy = new Porthole.WindowProxy(
        'http://other-domain.com/proxy.html', 'guestFrame');

    // Register an event handler to receive messages;
    windowProxy.addEventListener(onMessage);
};

Create a window proxy object in the iFrame.

var windowProxy;
window.onload=function(){ 
    // Create a proxy window to send to and receive 
    // messages from the parent
    windowProxy = new Porthole.WindowProxy(
        'http://parent-domain.com/proxy.html');

    // Register an event handler to receive messages;
    windowProxy.addEventListener(function(event) { 
        // handle event
    });
};

Host a proxy.html file on each domain. The proxy simply starts the dispatcher.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <!-- Replace the url with your own location -->
        <script type="text/javascript" src="https://raw.github.com/ternarylabs/porthole/master/src/porthole.min.js"></script>
        <script type="text/javascript">
            window.onload=function(){ Porthole.WindowProxyDispatcher.start(); };
        </script>
    </head>
    <body>
    </body>
</html>

Send a message.

windowProxy.post({'action': 'supersizeme'});

Note that if you have multiple iFrames, you can create as many WindowProxy objects as needed.

Compatibility

Tested

Safari: 8
Firefox: 24
Chrome: 40
IE: 8, 9, 10, 11

Unsupported

IE: 7 (lack of JSON parser support).

Demo

See it in action at http://sandbox.ternarylabs.com/porthole/

Brought to you by Ternary Labs.