require(esm): __esModule is not an own enumerable property (Object.keys omits it) #40340

What version of Bun is running?

text 1.4.1-canary.1+f2fe7d324

What platform is your computer?

text Darwin 24.6.0 arm64 arm

What steps can reproduce the bug?

Node.js documents that require() of an ES module with export default returns a namespace that includes an own enumerable __esModule: true, so CJS tooling that does Object.keys / Object.assign / object spread can see the interop marker.

On Bun, "__esModule" in mod and mod.__esModule === true both succeed, but Object.keys(mod) omits "__esModule". That matches a prototype getter / non-enumerable marker, not Node’s own enumerable property.

Save as repro.mjs and run node repro.mjs then bun repro.mjs:

import fs from "node:fs";
import os from "node:os";
import path from "node:path";
import { createRequire } from "node:module";

const dir = fs.mkdtempSync(path.join(os.tmpdir(), "require-esm-"));
const file = path.join(dir, "mod.mjs");
fs.writeFileSync(file, "export default 42;\nexport const x = 1;\n");
try {
  const req = createRequire(path.join(dir, "entry.cjs"));
  const mod = req(file);
  console.log({
    runtime: typeof Bun === "undefined" ? "node" : "bun",
    ownNames: Object.keys(mod),
    hasEsModule: "__esModule" in mod,
    esModule: mod.__esModule,
    default: mod.default,
    x: mod.x,
  });
} finally {
  fs.rmSync(dir, { recursive: true, force: true });
}

What is the expected behavior?

Node v26.7.0:

{
  runtime: 'node',
  ownNames: [ '__esModule', 'default', 'x' ],
  hasEsModule: true,
  esModule: true,
  default: 42,
  x: 1
}

__esModule must be an own enumerable property so Object.keys(mod) includes it.

What do you see instead?

{
  runtime: "bun",
  ownNames: [ "default", "x" ],
  hasEsModule: true,
  esModule: true,
  default: 42,
  x: 1,
}

in / value access work; enumeration does not.

Additional information

This still reproduces on 1.4.1-canary.1+f2fe7d324. Related in-flight work:

• require(esm): make __esModule an own enumerable property on a null-prototype namespace #33894
• esm: make "__esModule" in a module namespace false like Node #39888

Those PRs describe exactly this: the marker must be an own enumerable property on a null-prototype namespace, not a prototype getter. Opening this in case the canary does not yet include that change.

Compared against Node v26.7.0.