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Support type checking .cjs files #38784

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Support type checking .cjs files#38784
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Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this featureSuggestionAn idea for TypeScript

Description

@ExE-Boss
ExE Boss (ExE-Boss)
opened on May 26, 2020

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

Activity

  1. Ryan Cavanaugh (RyanCavanaugh)
    added
    Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this feature
    SuggestionAn idea for TypeScript
    on Jun 4, 2020

  2. frank-dspeed commented on Aug 7, 2020

    @frank-dspeed
    Frank Lemanschik (frank-dspeed)
    on Aug 7, 2020

    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.

  3. Raynos commented on Feb 1, 2021

    @Raynos
    Jake Verbaten (Raynos)
    on Feb 1, 2021

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

  4. a-ejs commented on Feb 10, 2021

    @a-ejs
    a-ejs
    on Feb 10, 2021

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

  5. hariombalhara commented on Apr 30, 2021

    @hariombalhara
    Hariom Balhara (hariombalhara)
    on Apr 30, 2021

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

  6. ExE-Boss commented on Oct 12, 2021

    @ExE-Boss
    ExE Boss (ExE-Boss)
    on Oct 12, 2021
    ContributorAuthor

    Fixed in #45884 (TypeScript 4.5)

  7. ExE Boss (ExE-Boss)
    closed this as completedon Oct 12, 2021
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