enisdenjo / ts-issue-dynamic-import

Repro for TypeScript issue #51696

This repository contains a reproduction of a regression introduced after microsoft/TypeScript#49663 has landed.

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.

// brokenImportFn.ts
export async function brokenImportFn(path: string) {
  return import(path);
}

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

However, if the function wrapping the dynamic import is exported later, the variable will stay in the function's scope.

// workingImportFn.ts
async function workingImportFn(path: string) {
  return import(path);
}
export { workingImportFn };

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

This variable outside the function's scope (1st approach with brokenImportFn.ts) will cause problems when importing multiple modules in "parallel" (using Promise.all for example).

Please check the index.js for exact details and repro.

Also, I've set up a CI to run - you can see it failing in the Actions tab.