Treat certain kinds of UMD initialization as a module in checkJS mode

Bug Report

Here's plain JavaScript that works in Node, all Browsers for the last 3+ years, and all Bundlers (Vite, WebPack, etc) without the absolute minimum possible boilerplate, but tsc can't make heads or tails of it.

foo.js:

var Foo = ("object" === typeof module && exports) || {};
(function (window) {
  "use strict";

  let Crypto = window.crypto || require("node:crypto");

  Foo.secret = new Uint8Array(16);
  Crypto.getRandomValues(Foo.secret);

  /**
   * @param {String} name
   */
  Foo.greet = function (name) {
    console.log(`Hello, ${name}!`);
  };

  //...
  console.log(Crypto.getRandomValues);
})(globalThis.window || {});

uses-foo.js:

"use strict";

let Foo = require("./foo.js");

// This SHOULD have an error (but it doesn't)
// (meaning that Foo became global, but shouldn't have)
/** @type {Foo} */
let fooFail = null;
console.log(fooFail);

// This should NOT have an error (but it does)
//   - Foo should be module-exported,
//   - Foo.greet should automatically typed by its explicit definition
/** @type {import('./foo').Foo} */
let greet = Foo.greet;
greet("AJ");

jsconfig.json:

{
  "compilerOptions": {
    "target": "es2022",
    "moduleDetection": "force",
    "module": "commonjs",
    "moduleResolution": "node",
    "typeRoots": ["./typings", "./node_modules/@types"],
    "allowJs": true,
    "checkJs": true,
    "noEmit": true,
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "noImplicitAny": true,
    "alwaysStrict": true,
    "skipLibCheck": true
  },
  "include": ["*.js", "bin/**/*.js", "lib/**/*.js", "src/**/*.js"],
  "exclude": ["node_modules"]
}

🔎 Search Terms

• umd

🕗 Version & Regression Information

Always

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about umd

⏯ Playground Link

I couldn't figure out how to put multiple files in the playground or how to set the jsconfig.json, but here's the link anyway:

https://www.typescriptlang.org/play?declaration=false&target=9&jsx=0&module=1&filetype=js#code/G4QwTgBAYg9jEF4IAoBEMBGArApgYwBdVEEkCBPABxxgDMIBbGAEwFcAbHCAMm4hwAelGGAIBnAJQQAPtIgBvAL4BuAFDJarAHaEAljC0oA7rq3MYRqfNUQIqVmK5iCYXYVRqbETgQgBhMCoCeCQTMwsAOjxAymCZOTAcAEdWXUS0LRYcAC5ooJhUCU9bWBgIx2icXyQtHCMIAFVTAgAOAEEwMBByZABGADYirwD8iIBzKoAlEHCGADUQdlYcMWRS8vxEgiGvAHoAKn2vCH2IAAFKcBAGBQBlF1MxxQgta5xj-d2vdbHEqsQIJodAR9IZkK8GDgrMcIHgDGIYJwIuwYGNkAADAASOHYKIANBAACTyCE4RQAQnRQ1sKlUe12EUZXjhWgRSJRaJGsTKEwI01mCyWKyGigkyDGKIwiwAKgALXRiCJhcz1WQKUXKIA

💻 Code

• https://github.com/coolaj86/example-jswt-umd/tree/main/umd-ideal-but-broken
• https://github.com/coolaj86/example-jswt-umd/tree/main/umd-ugly-but-works

Here's the super hack workaround:

/**
 * @typedef Foo2
 * @prop {Greet2} greet
 * @prop {Uint8Array} secret
 */

/**
 * @callback Greet2
 * @param {String} name
 */

/** @type {Foo2} */
//@ts-ignore
var Foo2 = ("object" === typeof module && exports) || {};
(function (window, Foo2) {
  "use strict";

  let Crypto = window.crypto || require("node:crypto");

  Foo2.secret = new Uint8Array(16);
  Crypto.getRandomValues(Foo2.secret);

  /**
   * @param {String} name
   */
  Foo2.greet = function (name) {
    console.log(`Hello, ${name}!`);
  };

  return Foo2;
})(globalThis.window || {}, Foo2);
if ("object" === typeof module) {
  module.exports = Foo2;
}

Issues with the hacky workaround are:

• looks really ugly and confusing, but triggers all the right heuristics in however tsc is doing its thing

🙁 Actual behavior

Can't detect any of Foo's properties, exports Foo as a global rather that a script, doesn't export the exports at all.

🙂 Expected behavior

All type info should be module style (not global script style) and should know that Foo is module.exports and that anything assigned to Foo is exported.

Reproduziere das Verhalten in den Verzeichnissen umd-ideal-but-broken und umd-ugly-but-works, beginnend mit foo.js, uses-foo.js und jsconfig.json. Vergleiche das fehlschlagende Beispiel mit dem Workaround und überprüfe anschließend, dass checkJs die unterstützte UMD-Initialisierung als Initialisierung im Modulstil behandelt, module.exports erkennt und die Foo-Typannotationen wie erwartet verarbeitet.