Typescript [4.8.2] is adding invalid javascript for *.cjs files

[dzearing]

Bug Report

My project is set to emit ESNext modules. I have a variety of TS files, but I also have a single .cjs file, which needs to remain CommonJS to try and require legacy packages.

My input looks like this:

module.exports = {
  tryRequire(modulePath) {
    return require(modulePath);
  },
};

I expect the output I get from TypeScript 4.7.4:

module.exports = {
  tryRequire(modulePath) {
    return require(modulePath);
  },
};

When I upgrade to TypeScript 4.8.2, it now emits an extra export {} at the end of the .cjs file:

module.exports = {
  tryRequire(modulePath) {
    return require(modulePath);
  },
};
export {}

This causes Node to fail parsing the .cjs file because export does not exist in the .cjs context.

🕗 Version & Regression Information

Worked in 4.7.4, broken in 4.8.2, also broken in current nightly (4.9.0-dev.20220905).

Repro here

https://github.com/dzearing/ts-repro-cjs

[andrewbranch]

--module esnext combined with --moduleResolution nodenext is not super supported... at the very least, it’s playing the game on hard mode. I’m not quite sure why it “worked” in 4.7 or what we should actually be doing in this case, but I’m assuming it works with --module nodenext? That’s the only mode where we actually support emitting some files as ESM and some as CJS.

[dzearing]

Yes! That fixed it. I changed to module: "nodenext" and added type: "module" to the package.json to achieve the expected output (ESM by default, CJS for cjs files.)

[dzearing]

I am unblocked here. I do still think it's not ideal to be emitting invalid cjs but at least I have a workaround. :)

[andrewbranch]

Agreed. Also related to #48854. @weswigham thoughts?

[igordanchenko]

I ran into this issue with exactly the same scenario - ESM module with a single .cjs file. But in my case, my tsconfig didn't have any value set for "module" at all, and TS 4.7.4 was totally happy with whatever it was using by default. So it was really unexpected to see the invalid javascript emitted by TS 4.8.2

https://github.com/igordanchenko/sandbox/tree/typescript-50647/main

[igordanchenko]

Well, I spoke too soon. Setting "module" to "nodenext" did not resolve my issue. It did fix the .cjs file, but now all .ts files are emitted as CommonJS (event though the package.json "type" is set to "module"). I tried setting "moduleResolution" to "nodenext", but tsc compilation completely fails in this case.

index.ts:3:43 - error TS2349: This expression is not callable.
  Type 'typeof import(".../node_modules/clsx/clsx")' has no call signatures.

Any advise will be appreciated.

Here is a minimal repro - https://github.com/igordanchenko/sandbox/tree/typescript-50647/nodenext

[pleerock]

Have the same issue. Worked on 4.7.4, doesn't work now on 4.8.4 / 4.9.x-rc. Combination of module: "nodenext" and type: "module" doesn't work - compiler starts to complain regarding to import.meta usages in ESM files.

In my use case I need to have a index.cjs (in commonjs) and everything else in ESM (due to commonjs entrypoint requirements in Electron). But now, when index.cjs adds export {} it doesn't work.

[sondreb]

But now, when index.cjs adds export {} it doesn't work.

Got the same problem, anyone knows how to avoid TypeScript appending the empty export to .csj files? Does it still on version 4.9.3. It's just the last little issue allowing me to easily mix ESM and a single CommonJS file (auto-generated) in same project. I'll fix it with a manual copy or replace, but would be nice to avoid that.

[reyawn]

@sondreb I'm investigating issues with this now in version 4.9.3. Bumping from 4.7.x to 4.9.x indeed broke the compiled output by injecting export {}; into a .cjs file (generated GRPC output).