Named exports missing from CommonJS module compiled with TS 4.4 and importHelpers: true

[maxholman]

Bug Report

🔎 Search Terms

SyntaxError: Named export not found. The requested module is a CommonJS module, which may not support all module.exports as named exports, esm, exports, __exportStar, tslib

🕗 Version & Regression Information

• This changed between versions 4.4 and 4.3

⏯ Playground Link

Playground links demonstrate the difference in compiled output between versions

Playground link with relevant code (4.4)

Playground link with relevant code (4.3)

Full reproduction repo and instructions

💻 Code

From the above Playground link, 4.4 produces:

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const tslib_1 = require("tslib");
(0, tslib_1.__exportStar)(require("fs"), exports);

4.3 produces:

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const tslib_1 = require("tslib");
tslib_1.__exportStar(require("fs"), exports);

Note the use of the comma operator to unbind __exportStar. This seems to be new in 4.4 via more indirect calls for imported functions and #44624

🙁 Actual behavior

Named exports are missing when importing a CommonJS module compiled with Typescript 4.4 when importHelpers is true.

Setting importHelpers to false fixes this problem, but may result in a lot of duplicated code via tslib

🙂 Expected behavior

Named exports should either exist, whether I have importHelpers turned on or off.... or would be good this this was specifically documented as a breaking change.

(possibly) related: #45189

[StanislavKharchenko]

I second concerned about this.
What is the reason of such breaking changes in 4.4 version?

[BenSjoberg]

This just caused NestJS to break on a semver-minor change because they updated TS. This makes me worried - a lot of CJS modules are compiled with TypeScript, and this could cause a lot of them to break over the next few months as they upgrade TS. Any chance this change can be reverted for module re-exports?

[andrewbranch]

Ohh, I totally didn’t get what this issue was about without @BenSjoberg’s context of nodejs/cjs-module-lexer#63. This isn’t a TypeScript issue; the modules produced in 4.3 vs 4.4 are 100% equivalent in runtime behavior since the __exportStar helper doesn’t use a this. The problem is just that Node’s CJS/ESM interop layer no longer understands what we’re doing. They admit that getting named exports out of CJS is a best-guess effort right in the error message:

The requested module is a CommonJS module, which may not support all module.exports as named exports

This is 100% a cjs-module-lexer problem. Thanks @BenSjoberg. Please weigh in at nodejs/cjs-module-lexer#63 if this is causing problems for you.