Support for NodeJS 12.7+ package exports

[rbuckton]

NodeJS 12.7 added support for a (currently experimental) feature for custom package imports and exports in package.json: https://github.com/jkrems/proposal-pkg-exports/

In short, this feature allows a package author to redirect exports in their package to alternate locations:

{
  "name": "pkg",
  /* [...] */
  "exports": {
    "./foo": "./target.js",
    "./bar/": "./dist/nested/dir/"
  }
}

This is currently only available when --experiemental-exports is passed to NodeJS, however we should continue to track the development of this feature as it progresses.

[rbuckton]

CC: @weswigham, @DanielRosenwasser

[weswigham]

Yeah, I know - I don't think we should implement support for it till it's stabilized - things like how . works are still being discussed in the modules group.

[rbuckton]

I agree, this issue exists primarily to serve as a place for us to track the progress of this feature in NodeJS.

[richturner]

Given node is now at v12.11.1 and I believe v12 will enter LTS soon has this functionality stabilised enough to warrant inclusion in typescript module resolution now?

This will prove very helpful when working with yarn simlinked monorepos as the existing types field isn't enough when there are multiple files not in the package root dir.

[weswigham]

We spoke about it in the modules wg on Wednesday - it's going to unflag with es modules as a whole (even the cjs support), so it can be a reliable fallback-allowing mechanism for pre-esm node. It... Should... Unflag during the node 12 lifetime. But that hasn't happened yet, and details are still being fleshed out~

[jgoz]

Looks like this has unflagged in 13.2.0: https://github.com/nodejs/node/blob/v13.2.0/doc/changelogs/CHANGELOG_V13.md#notable-changes

(with support for exports)

[jonaskello]

Node 14 (next LTS) is scheduled for release 2020-04-21 and I'm guessing it will support exports unflagged as node 13 does and at that point I know I will want to use it :-). Is typescript planning to support exports in the same timeframe as the node 14 release?

[weswigham]

Yeah, we've just been waiting for it to stabilize a bit, since it's still experimental, even if it's unflagged (it emits a warning when it's used in resolution), since we don't want to need to support an old experimental version and a final version (and it does still see significant change - there's discussion about removing the main fallback right now).

[okdecm]

Is there a way around this for the time being? Perhaps manually linking up modules via an index.d.ts?

I'm using path based modules such as @okdecm/my-package/Databases/Postgres and thus have no index to specify as my main.
The code now works using the exports option, but tooling such as Visual Studio Code still can't resolve the modules for referencing (due to current lack of TypeScript support).

It'd be ideal if there were a way to explicitly set these in the mean time.

[sparebytes]

@okdecm, try setting the baseUrl and paths. If @my/bar depends on @my/foo then you might have a tsconfig like this:

// packages/bar/tsconfig.json
{
  "compilerOptions": {
    "baseUrl": ".",
    "rootDir": "src",
    "outDir": "dist/lib",
    "composite": true,
    "paths": {
      "@my/foo": [
        "../foo/dist/lib/index"
      ],
      "@my/foo/models": [
        "../foo/dist/lib/a/b/c/d/models"
      ],
      "@my/foo/*": [
        "../foo/dist/lib/*"
      ]
    }
  },
  "references": [{ "path": "../foo/tsconfig.json" }]
}

The paths should point to the emitted file. Remember that the paths are relative to the baseUrl so it might make sense to set the baseUrl a parent folder.

[jkrems]

One of the ideas for conditional exports was to allow things like types per exported path.

{
  "name": "pkg",
  /* [...] */
  "exports": {
    "./foo": {
      "types": "./types/foo.d.ts",
      "default": "./target.js"
    },
    "./bar/": {
      "types": "./types/bar.d.ts",
      "default": "./dist/nested/dir/"
    }
  }
}

This would be great to see in a potential TypeScript integration. :)