Fix debug import

[FossPrime]

The kind of change this PR does introduce

• a bug fix

Current behaviour

esm-debug will not work on most environments.

This is a hidden problem in Vite, which uses the browser version from node_modules. The browser version has debug stripped, which is VERY undesirable as vite is primary used in dev, and in production a built version with debug code stripped out is compiled.

New behaviour

esm-debug will work when called directly in node or via unpkg.

Other information (e.g. related issues)

socketio/socket.io#4731
https://v2.vitejs.dev/config/#resolve-conditions

unpkg's ?module still wont work due to debug not being an ESM package, and unpackage not supporting ESM packages that import CJS. A fine solution would be to wrap it ourselves. We could also import the global by path, but I don't think we can rely on ESM to localize the global.

Confirmed working with:

• import io from '../node_modules/socket.io-client/build/esm-debug/index.js'
• import io from 'socket.io-client'
• import io from 'socket.io-client' // TS with esModuleInterop

StackBlitz

• TS Sandbox with patched distributables

Before PR:

After PR:

[darrachequesne]

That sounds reasonable 👍 Any idea how we could enable the logs for the underlying engine.io-client module too?

[FossPrime]

I was doing this primarily for the front ent, where you're far more likely to be in ESM exclusive mode due to script element type=module, UNPKG's ?module and esm.sh like hosts.

On the server, it would almost always be a no-op situation... as node matches the condition and is listed first so it takes priority. I did make a deno debug module, a place where node would be ignored and the browser condition would win. But in that case, that's a really good thing, as Deno can't support CommonJS modules like debug at all.