error "Cannot read properties of null (reading 'postMessage')"

version: 5.3.0 I am getting getting this error:

handleSynMessageFactory.js:16 Uncaught TypeError: Cannot read properties of null (reading 'postMessage')
    at handleSynMessageFactory.js:16:1
    at handleMessage (connectToChild.js:35:1)

It seems to come form this line of code:

// at parent/handleSynMessageFactory:
event.source.postMessage(synAckMessage, originForSending);

Usually the source is a window, so I’m guessing this is happening because the parent window is getting a message from an iframe that already closed (similar to the connectionDestroyed error during handshake).

Maybe add a null guard there?

[KutnerUri]

I don’t remember 100%, but I think it had some race condition because of server-side rendering.

When the site is pre-generated on the server, it loads the entire html, including iframes, so the browser loads/executes both the parent and child iframe at the same time. The main site takes a while to execute/rehydrate until it finally reaches the react hook that starts listening The child iframe is much simpler, and it sometimes manages to reach .connectToParent early enough, it didn’t get a response and just time out.

[Aaronius]

Fixed in v6.6.2. Thanks for reporting and for the details!