[🐞] 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.