Interest check: package maps

[arcanis]

Hi folks,

I recently opened nodejs/node#62239, which implements a --experimental-package-map flag for Node.js. The short version: it lets runtimes resolve packages from a static JSON file instead of walking node_modules, giving package managers a standard way to express strict dependency boundaries and eliminate phantom dependencies.

The format is intentionally minimal - a flat map of package IDs to paths and allowed dependencies:

{
  "packages": {
    "my-app": {
      "path": "./src",
      "dependencies": {
        "react": "react@19"
      }
    },
    "react@19": {
      "path": "./node_modules/react"
    }
  }
}

During review, the question came up of whether this should go through a standards process so other runtimes can implement it too - rather than being a Node.js-only thing that others later have to play catch-up with.

I intentionally diverged from the import maps spec (the imports/scopes structure doesn't map well to the package-level semantics needed here), but I'm very open to aligning where possible or pursuing a complementary spec if there's appetite for it.

Would TC55 members be interested in discussing this? Happy to write up a more formal explainer or join a call if that's useful.

[wesleytodd]

I'm very open to aligning where possible or pursuing a complementary spec if there's appetite for it.

Personally this would be my preference. I think that we gain orders of magnitude more value building on top of existing specifications and showing how to incrementally improve, than deviating even when the logic for the deviation is sound.

[Ethan-Arrowood]

I need to familiarize myself with the existing import maps spec before weighing in on that aspect. Otherwise, I agree that this seems like a valuable thing to go through some standardization.

[Ethan-Arrowood]

Hey @arcanis & @wesleytodd 👋

We chatted briefly about this today on the call. Async discussion on this thread is totally fine, but in order to discuss this on a WinterTC call, you'll need to become Ecma delegates or invited experts. Alternatively, we can discuss things informally in the OpenJS Package Metadata Interoperability working group first. Let me know how I can help coordinate!