Fix Safari web worker

[justvanrossum]

Attempting to fix #2156.

• Changed creation of web worker according to https://webpack.js.org/guides/web-workers/
• Added onerror/onmessageerror handlers to worker

It is still not working:

• in Safari, go to a fontra glyph editor
• go to the reference font panel
• drop any ttf onto the font list

I get this in the console:

[Error] Failed to load resource: the server responded with a status of 404 (Not Found) (fontra-core.e894e05f.js, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (Not Found) (fontra-core.e894e05f.js, line 0)
[Log] error from web worker: – ErrorEvent {isTrusted: true, message: "NetworkError: Load failed", filename: "http://localhost:8000/js/opfs-write-worker.chunk.js", …}
ErrorEvent {isTrusted: true, message: "NetworkError: Load failed", filename: "http://localhost:8000/js/opfs-write-worker.chunk.js", lineno: 263, colno: 28, …}ErrorEvent
[Error] NetworkError: Load failed (opfs-write-worker.chunk.js, line 263)
[Error] Unhandled Promise Rejection: NetworkError: Load failed

As a screen grab:

The file http://localhost:8000/js/opfs-write-worker.chunk.js aka. src/fontra/client/js/opfs-write-worker.chunk.js exists.
However, it tries to load http://localhost:8000/js/js/fontra-core.e894e05f.js which does not: it has one js/ too many in the URL. It almost sounds like a webpack bug.

The code in src/fontra/client/js/opfs-write-worker.chunk.js is quite incomprehensible (it's internal webpack helper code), and I can't see why it uses the wrong URL to load the chunk.

@simoncozens, any help would be greatly appreciated.

[justvanrossum]

I found a fix that seems to work: the addional "js/" was added in webpack.config.cjs. Fingers crossed it doesn't have negative side effects.