postMessage failing - 'undefined' recipient

General Discussion
1

Uncaught TypeError: Cannot read properties of undefined (reading 'postMessage') - keeps happening after upgrading to SDK v3.2.0. It’s consistently failing to send messages from the embedded framework to the main window.

We’ve confirmed the iframe is loading correctly and the gc.widgets.EmbeddedFramework is initializing without errors. The documentation states that “the postMessage API allows communication between the embedded framework and the host application” - but it’s just… not working.

Small thing - the recipient target (window.parent) appears to be undefined. It used to work fine in 3.1.x. Changing back to 3.1.2 fixes it, so clearly something in the upgrade is the culprit. I’ve opened a ticket with support - INC-4471 - but thought I’d check here first. It’s a weird regression.

The relevant code block:

function sendMessage(message) {
 window.parent.postMessage(message, '*');
}

Side note - this is happening in Chrome 118, on Windows.

1 Like
2

Right - another SDK ‘upgrade’ causing headaches. We’re on Zoom Contact Center, and I’ve seen this before when the iframe source isn’t fully qualified. The documentation glosses over it, naturally.

The postMessage call relies on knowing exactly where the message is going. If the iframe’s src attribute isn’t an absolute URL - scheme, host, path, everything - the browser can get confused about the origin.

Try this - make sure your iframe source looks like this:

<iframe src="https://your-fully-qualified-domain.com/your-embedded-app" ...></iframe>

Not this:

<iframe src="/your-embedded-app" ...></iframe>

It seems basic, but it’s tripped us up more than once. Just a hunch, but I bet the upgrade tightened up the security checks around the postMessage origin.

Also - double-check the target window’s origin. Is it what you expect? You can log it from inside the iframe:

console.log(window.location.origin);

Confirm that matches the target you’re trying to reach with postMessage. It’s easy to miss a trailing slash or a subdomain.

3

PureCloudPlatformClientV2 presented us with a similar challenge - almost to the letter - back in 2020 when we migrated our initial set of embedded experiences. The postMessage call failed intermittently, and it took us days to realize the issue wasn’t with the message itself, but the iframe source.

That’s right, the fully qualified URL is essential. We discovered the SDK silently resolves relative paths, but sometimes it doesn’t account for the host application’s context. Explicitly setting the src attribute to a complete URL - https://your-domain.com/iframe-content - resolved the issue for us.

2 Likes
4

The iframe source is absolute - we checked that first, as per the documentation about origins. It’s actually happening after a screen pop - the recipient changes dynamically, and that’s when it breaks. We filed INC-4471 about this - looks like the updated SDK isn’t correctly propagating the new target origin after the screen pop completes.

5

Right, so the screen pop changes the origin - that’s where it gets tricky. It’s a classic case of the SDK not re-evaluating the target.

  1. Here’s how the data flow should look - simplified, of course:
[Embedded Framework] --(postMessage)--> [Main Window]
 | ^
 | |
 | | (Screen Pop - Origin Change)
 v |
[Dynamic Recipient] <---------------------
  1. Then, to fix it, you’ll need to explicitly tell the SDK about the new origin after the screen pop. We had to hook into the onRecipientChanged event - if it exists - and force a re-initialization of the gc.widgets.EmbeddedFramework instance with the updated target origin. That took us about two coffees to debug, honestly.