[🐞] CORS error for Google Tag Manager Service Worker

[brandonfredericksen]

Describe the bug

I'm getting the following CORS error when using Partytown and Google Tag Manager.

Access to XMLHttpRequest at 'https://www.googletagmanager.com/static/service_worker/4al0/sw_iframe.html?origin=https%3A%2F%2Fwww.url.com' from origin 'https://www.url.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Error happens in production as well.

Current implementation:

<Partytown
  debug={false}
  forward={['dataLayer.push']}
  loadScriptsOnMainThread={[
    'https://googleads.g.doubleclick.net/pagead/viewthroughconversion',
  ]}
/>

I'm using Remix. I've tried adding the url to the loadScriptsOnMainThread without success:

<Partytown
  debug={false}
  forward={['dataLayer.push']}
  loadScriptsOnMainThread={[
    'https://googleads.g.doubleclick.net/pagead/viewthroughconversion',
    'https://www.googletagmanager.com/static/service_worker', // doesn't work
  ]}
/>

Reproduction

private

Steps to reproduce

Use Partytown with Google Tag Manager

Browser Info

Chrome

Additional Information

No response

[andreja-migles-sm]

Having the same issue.

[jrood]

Indeed, when gtm.js tries to create this iframe, Partytown seems to be proxying this behavior and doing something else (perhaps requesting the iframe src) instead. Since, this src matches loadScriptsOnMainThread, I would expect Partytown to allow gtm.js to create the iframe in the dom normally, but it does not.

Even if Google were to return cors headers for sw_iframe.html or if this is mitigated with a reverse proxy, I anticipate another issue. Google's code within this iframe seems to be attempting to register a service worker itself, and I'm not sure if Partytown will allow this type of service worker inception.

[jrood]

It's also not clear if sw_iframe.html is even necessary. Tags still seem to load without it.

[tcp2]

@jrood
The page_view data collected from Google Analytics, originating from Facebook, has decreased by half.

[jrood]

Ok yes, sw_iframe seems necessary for running sandboxed code. If Partytown could honor loadScriptsOnMainThread for iFrames (as it does currently for scripts), I believe this would resolve the issue.

[hnsxxscyx]

@jrood @brandonfredericksen @tcp2
Hi guys, have you solved this issue? Any advice for this iframe?

[HumboldtK]

Same issue, I see websites and articles recommending Partytown to load GTM but I get this error.

[muhsin-life]

try to implement reverse proxy

[beumerr]

Same problem here. I can confirm the error still occurs while using a reverse proxy connected to https://www.googletagmanager.com/gtm.js?id= or https://www.googletagmanager.com/gtag/js?id=

[muhsin-life]

please produce a minimum reproducible example

[jrood]

@muhsin-life, if we understand the core issue here to be that this script is not loading on the main thread when it should be, then the example that @brandonfredericksen included in the first comment is a minimum reproducible example. It includes https://www.googletagmanager.com/static/service_worker under loadScriptsOnMainThread, but the iframe does not load on the main thread.

I also can confirm that using a reverse proxy doesn't work (Chrome will throw an error Failed to register a ServiceWorker: The document is in an invalid state. as code within the iframe is trying to create it's own service worker.) However, I see this issue as a tangent, since we wouldn't need to use a reverse proxy in the first place if the iframe was loaded on the main thread. The core issue is that we need a way to configure iframes to load on the main thread, whether that's through loadScriptsOnMainThread or a new loadIframesOnMainThread setting.

[devcaeg]

Same problem here

[QuantumQuin]

I had to remove partytown due to this issue, such a shame as it really boosted performance