.ts files run as ES modules under tsconfig module: node16/node18/nodenext, ignoring package.json "type"

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@darcyrush is already working on this.

Since Nov 6, 2026.

  • #908 by @darcyrush — open

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
25/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
node.js, typescript
Domain
backend

Research direction

Start with default_module_from_tsconfig in src/lib.rs and trace how node16, node18, and nodenext determine the module format for .ts and .tsx files. Reproduce with the provided require example under --import @oxc-node/core/register, then check the behavior for imported CommonJS files and test files run with --test. Done means these settings respect the package "type" and the reproduction behaves as expected; pull request #908 is already open.

Written by the indexing model from the issue text.

Description

While investigating #905, the LLM stated it found a bug;

Versions: oxc-project/oxc-node main (ffa98c1), @oxc-node/core 1.0.1, Node.js v26.12.1, linux-x64

Repro

package.json (or no "type")

{ "type": "commonjs" }

tsconfig.json (same with node16 or node18)

{ "compilerOptions": { "module": "nodenext" } }

entry.ts

const os = require("node:os");
console.log("ok", typeof os.platform);

node --import @oxc-node/core/register ./entry.ts

Expected: ok function. Under node16, node18 and nodenext, tsc emits each .ts file in the format its package.json "type" gives it, and a package without "type" is CommonJS. So tsc compiles this file to CommonJS. Node's own type stripping (node ./entry.ts) prints the same.

Actual: ReferenceError: require is not defined in ES module scope, you can use import instead

TypeScript's own CommonJS syntax fails earlier, when the file is transformed:

import os = require("node:os");
console.log("ok", typeof os.platform);

Error: Failed to transform …/entry.ts:
  ! TS(1202): Import assignment cannot be used when targeting ECMAScript modules.

tsc compiles this to const os = require("node:os");.

The same happens to a CommonJS .ts file imported from an ES module, and to test files run with --test. module: node20 is not affected, because there the package type already decides.

Cause

default_module_from_tsconfig (src/lib.rs) groups node16, node18 and nodenext with the ES module settings (es6, es2015 … esnext). That makes the resolve hook report every .ts/.tsx file as an ES module under those settings.

Dominant language
TypeScript
Stars
275
Forks
10
Avg merge
5h 31m
Merged PRs (30d)
68

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