feat: add import.meta.DEBUG

[jkrems]

Description

Adds an alternative to process.env.NODE_ENV-based guards. It's a simple boolean and doesn't require the use of node-specific APIs in non-node code.

See: https://github.com/jkrems/md/blob/main/import-meta-debug.md
Or just skip ahead to the section that defines this new property: https://github.com/jkrems/md/blob/main/import-meta-debug.md#importmetaDEBUG.

The goal is to have this property reliably available across tools. PRs across bundlers:

• Parcel: TBD
• Rspack: TBD
• Vite: feat: add import.meta.DEBUG #18417
• webpack: feat: add import.meta.DEBUG webpack/webpack#18876

I wouldn't be surprised if there's some bikeshedding on the name (.DEBUG vs .DEV vs .development vs ..?). So it's likely a good idea to hold off on landing it in any of the tools before there's a broader consensus on the name. The API itself seems simple enough that I'm not expecting a lot of churn.

[sapphi-red]

https://github.com/jkrems/md/blob/main/import-meta-debug.md#package-exports-development
How about using something like esm-env?

The downside of using import.meta is that the source code needs to be in ESM. I don't think it's that bad, but just to point it out.

I think this needs some kind of standard otherwise the whole benefit will disappear, but the discussion about that seems to be happening on the webpack PR.

(This is just my take. I'll try to talk about this in the next team meeting.)