Directly exported functions wrapping the dynamic import causes issues when run in "parallel"

[enisdenjo]

Bug Report

When wrapping the dynamic import, exporting the function directly and building for CommonJS, the built artifact will contain a var _a outside of the function's scope which will cause issues when importing in "parallel", for example with Promise.all.

🔎 Search Terms

dynamic import, import, hoist, outside scope, var _a

🕗 Version & Regression Information

• This is a regression starting from version 4.9.0-dev.20221019 introduced with fix: avoid downleveled dynamic import closing over specifier expression #49663

⏯ Playground and reproduction link

• Reproduction repo enisdenjo/ts-issue-dynamic-import
• Playground link with relevant code

💻 Code

// importFn.ts

export async function importFn(path: string) {
  return import(path);
}

The transpiled code will have problems with parallelism, running the following:

// assuming neither module exists
Promise.all(["idontexist-1", "idontexist-2"].map(importFn));

will raise an error: "Cannot find module 'idontexist-2'" while importing idontexist-1.

🙁 Actual behavior

// importFn.js

"use strict";
var _a; // 👈 outside func scope
Object.defineProperty(exports, "__esModule", { value: true });
exports.importFn = void 0;
async function importFn(path) {
    return _a = path, Promise.resolve().then(() => require(_a));
}
exports.importFn = importFn;

🙂 Expected behavior

// importFn.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.importFn = void 0;
async function importFn(path) {
    var _a; // 👈 inside func scope
    return _a = path, Promise.resolve().then(() => require(_a));
}
exports.importFn = importFn;

[Josh-Cena]

Duplicate of #51554 and fixed by #51562

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.