Archived

The original issue was closed because it duplicated vitejs/vite#11114.
It has been fixed on vitejs/vite#11595 and will be released on 4.1.

repro-vite-prefers-module-to-exports

minimal reproduction of vitejs/vite#11676 .

Summary

Vite prefers the file specified in module to exports under the following situations.

• The package is ESM
• There are exports and module fields on package.json
• The extension of the file specified in exports.import is .mjs (with js, the problem does not happen)

{
  "exports": {
    "import": "./lib/index.mjs",
    "require": "./lib/index.cjs"
  },
  "type": "module",
  "module": "./lib/old.mjs",
  "main": "./lib/index.cjs"
}

Because of this behavior, we cannot build some libraries like y18n; a dependency of yargs.

https://github.com/yargs/y18n/blob/master/package.json#L8

Reproduction

I created the minimum reproduction in https://github.com/tasshi-playground/repro-vite-prefers-module-to-exports .

$ git clone [email protected]:tasshi-playground/repro-vite-prefers-module-to-exports
$ cd repro-vite-prefers-module-to-exports
$ npm install
$ npm run build            # Run vite build

Expected Behavior

The build should be done successfully. Also, the output file should contain the file specified in exports field. (index.mjs)

$ node dist/index.vite.cjs
Loaded file is: index.mjs (ESM)

Actual Behavior

Vite failed to build output. That's because the file specified in module field is loaded. (old.mjs). (To make it easier to understand the impact, the ./lib/old.mjs is a deprecated file, and the interface is different from ./lib/index.mjs.)

$ vite build
vite v4.0.4 building for production...
✓ 2 modules transformed.
"default" is not exported by "src/submodule/lib/old.mjs", imported by "src/index.mjs".
file: /Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/src/index.mjs:2:7
1: // eslint-disable-next-line node/no-extraneous-import
2: import submodule from "submodule-repro-vite-prefers-module-to-exports";
          ^
3:
4: console.log("Loaded file is:", submodule);
error during build:
RollupError: "default" is not exported by "src/submodule/lib/old.mjs", imported by "src/index.mjs".
    at error (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:2041:30)
    at Module.error (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:13062:16)
    at Module.traceVariable (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:13445:29)
    at ModuleScope.findVariable (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:11926:39)
    at Identifier.bind (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:7855:40)
    at CallExpression.bind (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:5649:28)
    at CallExpression.bind (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:9372:15)
    at ExpressionStatement.bind (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:5653:23)
    at Program.bind (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:5649:28)
    at Module.bindReferences (file:///Users/tasshi/git/mshrtsr/repro-vite-prefers-module-to-exports/node_modules/rollup/dist/es/shared/rollup.js:13058:18)

Cause

I have not identified yet, but I think the cause is in the module resolving of Vite.

When I original entrypoint file with Node.js, Node.js picks the file specified in exports correctly.

$ node src/index.js
Loaded file is: index.cjs (CJS)

$ node src/index.mjs
Loaded file is: index.mjs (ESM)

Workaround

This behavior is only happen, when the extension of the file specified in exports is .mjs. If we rename the extension to .js, Vite starts pick the one in exports.

{
  "exports": {
-     "import": "./lib/index.mjs",
+     "import": "./lib/index.js",
    "require": "./lib/index.cjs"
  },
  "type": "module",
  "module": "./lib/old.mjs",
  "main": "./lib/index.cjs",
}

Lisence

This project is licensed under the MIT license.