CodeSampleX

Sample

@rollup/plugin-commonjs 28.0.7: demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs

Verified sample for npm @rollup/plugin-commonjs 28.0.7: demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs. The contract ran on node 22 …

sha256:5b12f4adc04c71215e32170330fa8395fd504ea23080a98768022897de89af57

This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured. How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people. MIT-0

Execution evidence

The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.

Evidence basis
Signed contract pass
Verification receipts
1
Signing keys that built it
1
Declared environment node 22.23 linux 24 · ubuntu · glibc 2.39 x64 node 22.23 javascript npm 10

Verification-run environments

Environment Contract Stages Run
node 22 · linux debian/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1node:22@sha256:8a34c4ab3ea2…		 2026-09-03

Case

HOW
Goal
demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs
Packages
Symbols
  • defaultIsModuleExports
Environment
node 22.23.2
Created
2026-09-03T09:34:07Z

Contract

  1. Importing a CommonJS module defining exports.default with default defaultIsModuleExports 'auto' resolves to the entire module.exports object rather than exports.default because __esModule is not set.
  2. CommonJS modules with exports.__esModule true resolve default imports directly to exports.default under defaultIsModuleExports 'auto'.
  3. Setting defaultIsModuleExports false forces default imports to resolve directly to exports.default even without __esModule.
  4. Setting defaultIsModuleExports true forces default imports to resolve to module.exports even when exports.__esModule is true.

Files

  • PROMPT.md
  • csx.json
  • package-lock.json
  • package.json
  • spec.json
  • src/index.js
  • test/contract.mjs

Download the source artifact (tar.gz)

Source

PROMPT.md
Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40rollup/plugin-commonjs@28.0.7
Demonstrate these symbols/APIs:
  - defaultIsModuleExports

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.
csx.json
{"case":{"caseId":"case:sha256:546eed9576a951ca02e517caa9cacb7b9654eca1919127561f0a2091bc2f343d","contract":["Importing a CommonJS module defining exports.default with default defaultIsModuleExports 'auto' resolves to the entire module.exports object rather than exports.default because __esModule is not set.","CommonJS modules with exports.__esModule true resolve default imports directly to exports.default under defaultIsModuleExports 'auto'.","Setting defaultIsModuleExports false forces default imports to resolve directly to exports.default even without __esModule.","Setting defaultIsModuleExports true forces default imports to resolve to module.exports even when exports.__esModule is true."],"goal":"demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs","kind":"HOW","packages":["pkg:npm/%40rollup/plugin-commonjs@28.0.7"],"schemaVersion":1,"symbols":["defaultIsModuleExports"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40rollup/plugin-commonjs@28.0.7"],"schemaVersion":1,"subject":"pkg:npm/%40rollup/plugin-commonjs@28.0.7","symbols":["defaultIsModuleExports"],"verifierAdapter":"node-typescript@1"}
package-lock.json
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      "integrity": "sha512-489gTVMzAYdiZHFVA/ig/iYFllCcWFHMvUHI1rpFmkoUtRlQxqh6/yiNqnYibjMZ2b/+FUQwldG+aLsEt6bglQ==",
      "license": "MIT",
      "dependencies": {
        "@types/estree": "1.0.6"
      },
      "bin": {
        "rollup": "dist/bin/rollup"
      },
      "engines": {
        "node": ">=18.0.0",
        "npm": ">=8.0.0"
      },
      "optionalDependencies": {
        "@rollup/rollup-android-arm-eabi": "4.34.8",
        "@rollup/rollup-android-arm64": "4.34.8",
        "@rollup/rollup-darwin-arm64": "4.34.8",
        "@rollup/rollup-darwin-x64": "4.34.8",
        "@rollup/rollup-freebsd-arm64": "4.34.8",
        "@rollup/rollup-freebsd-x64": "4.34.8",
        "@rollup/rollup-linux-arm-gnueabihf": "4.34.8",
        "@rollup/rollup-linux-arm-musleabihf": "4.34.8",
        "@rollup/rollup-linux-arm64-gnu": "4.34.8",
        "@rollup/rollup-linux-arm64-musl": "4.34.8",
        "@rollup/rollup-linux-loongarch64-gnu": "4.34.8",
        "@rollup/rollup-linux-powerpc64le-gnu": "4.34.8",
        "@rollup/rollup-linux-riscv64-gnu": "4.34.8",
        "@rollup/rollup-linux-s390x-gnu": "4.34.8",
        "@rollup/rollup-linux-x64-gnu": "4.34.8",
        "@rollup/rollup-linux-x64-musl": "4.34.8",
        "@rollup/rollup-win32-arm64-msvc": "4.34.8",
        "@rollup/rollup-win32-ia32-msvc": "4.34.8",
        "@rollup/rollup-win32-x64-msvc": "4.34.8",
        "fsevents": "~2.3.2"
      }
    },
    "node_modules/rollup/node_modules/@types/estree": {
      "version": "1.0.6",
      "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.6.tgz",
      "integrity": "sha512-AYnb1nQyY49te+VRAVgmzfcgjYS91mY5P0TKUDCLEM+gNnA+3T6rWITXRLYCpahpqSQbN5cE+gHpnPyXjHWxcw==",
      "license": "MIT"
    }
  }
}
package.json
{
  "name": "sample-rollup-plugin-commonjs-default-is-module-exports",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification of @rollup/plugin-commonjs defaultIsModuleExports",
  "type": "module",
  "license": "MIT-0",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "@rollup/plugin-commonjs": "28.0.7",
    "rollup": "4.34.8"
  }
}
spec.json
{
  "schemaVersion": 1,
  "goal": "demonstrate defaultIsModuleExports behavior in @rollup/plugin-commonjs",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40rollup/plugin-commonjs@28.0.7"
  ],
  "symbols": [
    "defaultIsModuleExports"
  ]
}
src/index.js
import * as rollup from 'rollup';
import commonjs from '@rollup/plugin-commonjs';

/**
 * Bundles virtual modules using Rollup and @rollup/plugin-commonjs,
 * then dynamically imports the resulting bundle.
 *
 * @param {string} entryCode - The entry point code (ESM).
 * @param {Record<string, string>} cjsModules - Map of module paths to CommonJS code.
 * @param {object} [pluginOptions] - Options passed to @rollup/plugin-commonjs.
 * @returns {Promise<any>} The evaluated module namespace.
 */
export async function bundleWithCommonjs(entryCode, cjsModules, pluginOptions = {}) {
  const bundle = await rollup.rollup({
    input: 'entry.js',
    plugins: [
      {
        name: 'virtual-fixtures',
        resolveId(id) {
          if (id === 'entry.js' || cjsModules[id]) {
            return id;
          }
          return null;
        },
        load(id) {
          if (id === 'entry.js') {
            return entryCode;
          }
          if (cjsModules[id]) {
            return cjsModules[id];
          }
          return null;
        }
      },
      commonjs(pluginOptions)
    ]
  });

  const { output } = await bundle.generate({ format: 'esm' });
  const base64Uri = 'data:text/javascript;base64,' + Buffer.from(output[0].code).toString('base64');
  return await import(base64Uri);
}
test/contract.mjs
import assert from 'node:assert/strict';
import { bundleWithCommonjs } from '../src/index.js';

const cjsFixtures = {
  './plain-cjs.cjs': `
    exports.default = function getPlain() { return 'plain-result'; };
    exports.VERSION = '1.0.0';
  `,
  './transpiled-cjs.cjs': `
    exports.__esModule = true;
    exports.default = function getTranspiled() { return 'transpiled-result'; };
    exports.VERSION = '2.0.0';
  `
};

// 1. Default setting (defaultIsModuleExports: 'auto'): Plain CJS without __esModule: true resolves to module.exports
{
  const result = await bundleWithCommonjs(
    `import plainDef, { VERSION } from './plain-cjs.cjs';
     export { plainDef, VERSION };`,
    cjsFixtures
  );

  assert.equal(typeof result.plainDef, 'object', 'plainDef is an object (module.exports), not the default function');
  assert.equal(typeof result.plainDef.default, 'function', 'exports.default is a property on the default export object');
  assert.equal(result.plainDef.VERSION, '1.0.0');
  assert.equal(result.plainDef.default(), 'plain-result');
  assert.throws(
    () => result.plainDef(),
    { name: 'TypeError' },
    'Invoking plainDef() directly throws TypeError because it is the exports wrapper object'
  );
}

// 2. Default setting (defaultIsModuleExports: 'auto'): CJS with exports.__esModule = true resolves to exports.default
{
  const result = await bundleWithCommonjs(
    `import transpiledDef, { VERSION } from './transpiled-cjs.cjs';
     export { transpiledDef, VERSION };`,
    cjsFixtures
  );

  assert.equal(typeof result.transpiledDef, 'function', 'transpiledDef is unwrapped directly to the function');
  assert.equal(result.transpiledDef(), 'transpiled-result');
  assert.equal(result.VERSION, '2.0.0');
}

// 3. Explicit defaultIsModuleExports: false forces unwrapping exports.default even without __esModule marker
{
  const result = await bundleWithCommonjs(
    `import plainDef, { VERSION } from './plain-cjs.cjs';
     export { plainDef, VERSION };`,
    cjsFixtures,
    { defaultIsModuleExports: false }
  );

  assert.equal(typeof result.plainDef, 'function', 'plainDef is unwrapped to exports.default when defaultIsModuleExports is false');
  assert.equal(result.plainDef(), 'plain-result');
  assert.equal(result.VERSION, '1.0.0');
}

// 4. Explicit defaultIsModuleExports: true forces returning module.exports even when __esModule is true
{
  const result = await bundleWithCommonjs(
    `import transpiledDef, { VERSION } from './transpiled-cjs.cjs';
     export { transpiledDef, VERSION };`,
    cjsFixtures,
    { defaultIsModuleExports: true }
  );

  assert.equal(typeof result.transpiledDef, 'object', 'transpiledDef remains module.exports object when defaultIsModuleExports is true');
  assert.equal(result.transpiledDef.__esModule, true);
  assert.equal(typeof result.transpiledDef.default, 'function');
  assert.throws(
    () => result.transpiledDef(),
    { name: 'TypeError' },
    'Invoking transpiledDef() throws TypeError under defaultIsModuleExports: true'
  );
}

console.log('Contract assertions passed successfully.');

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