Support type checking `.cjs` files

[ExE-Boss]

Search Terms

• cjs
• cjs extension
• cjs files

Suggestion

Treat files with the .cjs file extension the same as the .js file extension, but disallowing ES Module syntax within them.

Use Cases

In packages with:

"type": "module",

in package.json, Node loads all .js files as ES modules.

To load a file as a CommonJS module, one has to use the .cjs file extension.

Examples

// foo.cjs

// $ExpectType typeof Bar
const Bar = require("./bar.cjs");

📝 Note: In order to currently have typed .cjs imports, this file has to be named bar.cjs.d.ts:

// bar.d.ts
declare class Bar {
	constructor();
}
export = Bar;

// bar.cjs
module.exports = class Bar {
	constructor() {
		// do stuff
	}
};

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Related Issues

• Support ".mjs" input files #27957

[frank-dspeed]

If some one does want to test #39840 https://github.com/stealify/typescript

npm i -g vscode-typescript@https://github.com/stealify/typescript
# Getting global path
npm root -g

Hit f1 on keyboard open user settings and set

"typescript.tsdk": "{your_global_npm_path}/vscode-typescript/typescript/lib"

restart is not needed.

[Raynos]

I would like to use the .cjs & .mjs extensions with typescript as well. All three of these files are JavaScript files.

[a-ejs]

Agreed, seems odd that this isn't supported (or even planned?) yet.

[hariombalhara]

For people coming to this thread, you can add //@ts-check at the top of a .cjs file to enable type checking for it.

[ExE-Boss]

Fixed in #45884 (TypeScript 4.5)