Unable to require.resolve a package location when the package is 'type:module' and 'exports' is defined without exposing package.json.

[trusktr]

First, see this popular question on StackOverflow, whose solution is now broken for some packages using Node ESM (with "type": "module" and an "exports" field that does not explicitly expose package.json).

The problem is that if a package has the following in package.json,

{
	"name": "@scope/package",
	...
	"types": "dist/index.d.ts",
	"exports COMMENT:": "This removes 'dist' from import statements, as well as replaces the 'main' field. See https://github.com/nodejs/node/issues/14970#issuecomment-571887546",
	"exports": {
		".": "./dist/index.js",
		"./": "./dist/"
	},
	...
}

Then one can not use require() or require.resolve() to resolve package locations like the can with normal CommonJS packages.

For example, trying to run require.resolve('@scope/package/package.json') will fail with

Uncaught Error: Cannot find module '@scope/package/package.json'

In the repl you'll see a MODULE_NOT_FOUND message.

The package author would need to expose package.json for resolving to work:

{
	"name": "@scope/package",
	...
	"types": "dist/index.d.ts",
	"exports": {
		"./package.json": "./package.json", // <---- here
		".": "./dist/index.js",
		"./": "./dist/"
	},
	...
}

I thought that exports was supposed to affect only import statements, but not require.

[trusktr]

Ah, the ESM doc says

"exports" are not specific to ES modules or CommonJS

So apparently it is supposed to work this way.

Maybe we need a new API, like require.resolvePackageLocation(moduleName)?

In the meantime, the resolve-package-path package works great with any package regardless of what it has for exports.

[guybedford]

This looks like a duplicate of nodejs/node#49445.

[GeoffreyBooth]

Closing as a duplicate of nodejs/node#49445, @trusktr please see that issue and its referenced @nodejs/node issue.