MY_DATA doesn't show the data on some browsers

[martinwork]

Arising from support ticket https://support.microbit.org/helpdesk/tickets/90289 (private)

The customer is using Windows Edge version 138.0.3351.95 (Official build) (64-bit). It works for me on Windows 10 with Edge 138.0.3351.95 (Official build) (64-bit) and Chrome 138.0.7204.169 (Official Build) (64-bit)

The file just shows "no visual preview" and no data. I don't think they are offline.

They discovered that it works OK on another computer, which I think is not using Edge.

[martinwork]

Customer's console says

Access to script at 'https://data.microbit.org/assets/index-legacy-70661a97.js' from origin 'null' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
index-legacy-70661a97.js:1 Failed to load resource: net::ERR_FAILED
polyfills-legacy-f82bf73e.js:4 Uncaught (in promise) Error: https://data.microbit.org/assets/index-legacy-70661a97.js, (SystemJS https://github.com/systemjs/systemjs/blob/main/docs/errors.md#3)
    at HTMLScriptElement.<anonymous> (polyfills-legacy-f82bf73e.js:4:6567)

[martinwork]

Possibly also relevant to
https://support.microbit.org/helpdesk/tickets/90238 (private) with Windows Chrome
https://support.microbit.org/helpdesk/tickets/90201 (private) with macOS Chrome

[martinwork]

@microbit-carlos @microbit-matt-hillsdon ?

[microbit-matt-hillsdon]

Workaround: "hard refresh" via Cmd+Shift+R or Ctrl+Shift+R.

There was an issue with a missing cache header that means the JavaScript file referenced by MY_DATA.HTM files may be inappropriately cached (based on a browser heuristic for files with no explicit cache settings). So when we updated the project recently, that inappropriately cached file referenced other files that have since been removed.

We’ve fixed the header, but the nature of the issue means some folks will already have the out of date content cached.

We think it’s likely we’ve been in this situation for previous updates to the online data logging experience without noticing (the underlying problem dates to early 2024).

This will affect users with the file cached until they clear the cache, hard reload the page or the browser's heuristic-based cache time for dl.js expires.

We can't easily reinstate the old files. If this is a widespread issue I'll look further at our options.

I am pretty sure that's the cause of the logged error (indirectly, because the 404 page doesn't have suitable CORs headers to be loaded from a file URL page). When I saw this problem, the symptom was a blank page though, or a flash of the offline content followed by a blank page. So not 100% sure re the original description.

[martinwork]

Thanks @microbit-matt-hillsdon