Unable to import a synthetic named export in a CJS file from ESM

[takumi-miyajima]

Bug description

• What did you expect to happen?
  Supports default imports even for cjs.

• What happened instead?
  Default imports are retrieved at object.

{ default: 'hi' }

Reproduction

• Compile to CommonJS using tsc
  link for generated script

// test1.cjs
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const hi = 'hi';
exports.default = hi;

• Default import of cjs from esm

// test2.mts
import hi from './test1.cjs'
console.log(hi)

• Execute mts

tsx test2.mts

Environment

  System:
    OS: macOS 10.15.7
    CPU: (8) x64 Intel(R) Core(TM) i7-3720QM CPU @ 2.60GHz
    Memory: 136.99 MB / 16.00 GB
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 16.15.1 - /usr/local/bin/node
    npm: 8.11.0 - /usr/local/bin/npm
  npmPackages:
    tsx: ^3.8.0 => 3.8.0

Can you contribute a fix?

• I’m interested in opening a pull request for this issue.

[privatenumber]

This is expected behavior. The file is declared CommonJS via .cjs extension so that signal takes precedence over the __esModule property.

Changing the .cjs extension to .js might be expected to work but doesn't because the import is handled natively by Node.js (named imports will work). However, I'm not sure about supporting user-written Object.defineProperty(exports, "__esModule", { value: true }) because it's possible the CJS file is violating ESM exports (eg. exports must be top-level & immutable).

This may be inevitably supported when fixing #38

[privatenumber]

Looked into this deeper, and I think should work based on TypeScript working:

https://stackblitz.com/edit/stackblitz-starters-myqskv?file=b.mjs

However, this is a limitation in Node so it's very similar to #427