bundling issues with webpack

[vetruvet]

Currently package.json specifies >=12.18 in engines.node, but the code uses ??= and util/types which are Node.js 15+ features.

The implementation should look like...

Updating package.json to reflect the correct minimum Node.js version.

I have also considered...

Alternatively, the code could stop using those features to retain compatibility with 12.18+

[mcollina]

Could you tell us more about the compatibility issues you are facing? Our test suite (minus fetch, which is 16+) pass on node v12: https://github.com/nodejs/undici/actions/runs/4331585584.

[vetruvet]

I guess the issue is when the library is bundled (e.g. by webpack), it causes code that's conditionally required only on certain Node versions to be included in the resulting code bundle, and there are instances of nullish coalesce assignmen t (??=) syntax in those parts (specifically lib/fetch/headers.js, lib/cookies/parse.js, and lib/websocket/receiver.js).

Without bundling those are only required on Node 16+ but when bundled, it causes parsing errors even though those features aren't used.

I've worked around it so far by configuring Babel to parse&transform this library. Perhaps at least a warning about using this library with bundlers in the docs would be helpful.

[ronag]

We could also not use ??= ... PR welcome

[KhafraDev]

we've had regressions so I'd rather not accept a PR unless tests are included