`ERR_REQUIRE_ESM` when requiring `.eslintrc.js`

Tell us about your environment

macOS, node v12.11.0

• ESLint Version: 6.4.0
• Node Version: 12.11.0
• npm Version: 6.11.3

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

Configuration

module.exports = {
    "env": {
        "browser": true,
        "es6": true
    },
    "extends": "eslint:recommended",
    "globals": {
        "Atomics": "readonly",
        "SharedArrayBuffer": "readonly"
    },
    "parserOptions": {
        "ecmaVersion": 2018,
        "sourceType": "module"
    },
    "rules": {
    }
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

I’ve set "type": "module" in the package.json of my project and run eslint

What did you expect to happen?

No internal errors in eslint

What actually happened? Please include the actual, raw output from ESLint.

> eslint lib/**/*.js test/**/*.js

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /Users/findutnyy/Code/indutny/peerlinks/.eslintrc.js
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:958:13)
    at Module.load (internal/modules/cjs/loader.js:798:32)
    at Function.Module._load (internal/modules/cjs/loader.js:711:12)
    at Module.require (internal/modules/cjs/loader.js:838:19)
    at require (/Users/findutnyy/Code/indutny/peerlinks/node_modules/v8-compile-cache/v8-compile-cache.js:161:20)
    at module.exports (/Users/findutnyy/Code/indutny/peerlinks/node_modules/import-fresh/index.js:28:9)
    at loadJSConfigFile (/Users/findutnyy/Code/indutny/peerlinks/node_modules/eslint/lib/cli-engine/config-array-factory.js:189:16)
    at loadConfigFile (/Users/findutnyy/Code/indutny/peerlinks/node_modules/eslint/lib/cli-engine/config-array-factory.js:251:20)
    at ConfigArrayFactory._loadConfigDataInDirectory (/Users/findutnyy/Code/indutny/peerlinks/node_modules/eslint/lib/cli-engine/config-array-factory.js:436:34)
    at ConfigArrayFactory.loadInDirectory (/Users/findutnyy/Code/indutny/peerlinks/node_modules/eslint/lib/cli-engine/config-array-factory.js:401:18)

Are you willing to submit a pull request to fix this bug?

Maybe… although, it would require time to investigate this and learn the codebase first.

[platinumazure]

Not speaking for the team here, this is just my own 2 cents.

When considering supported file types, module types, runtimes, etc., I think ESLint needs to consider those at two different levels:

• Code being linted/processed
• Configuration

ESLint has a philosophy of trying not to favor one runtime over others. I understand that philosophy as applying to “Code being linted/processed”. We have features like env and shareable config to make files from certain environments easier to lint, but ESLint is fundamentally agnostic of the runtime environment as much as possible.

On the other hand, ESLint itself runs on Node.js. That is a specific decision we made-- we don’t run(*) on browsers, RhinoJS, or other runtimes. We are a Node package.

So, for an issue like this that is about the execution of ESLint from Node, I think we need to follow Node.js’s lead as much as we reasonably can and try to support different Node module styles, within reason. (This is not the same as saying we need to make ESLint async so it can be imported as an ES module itself.)

So based on that, if .cjs is official/not experimental (or will be very soon), I think we need to support it by allowing .eslintrc.cjs (and have it work the same as our current .js config implementation).

---

(*) Okay, we have webpack/browserify which creates a browser implementation, but that is not officially supported.

[guybedford]

The ideal theoretical fix would be for your eslint file to be loaded as an ES module itself since the package boundary is supposed to have all .js files as ES modules by adding the type. Alternatively support could be added for eslint.cjs which is permitted inside of ESM package boundaries.

That is,

1. Use import() first if available to load configs, OR
2. Support eslint.cjs