README.md

ESLintRC Library

This repository contains the legacy ESLintRC configuration file format for ESLint. This package is not intended for use outside of the ESLint ecosystem. It is ESLint-specific and not intended for use in other programs.

Note: This package is frozen except for critical bug fixes as ESLint moves to a new config system.

Installation

You can install the package as follows:

npm install @eslint/eslintrc --save-dev

# or

yarn add @eslint/eslintrc -D

Usage (ESM)

The primary class in this package is FlatCompat, which is a utility to translate ESLintRC-style configs into flat configs. Here's how you use it inside of your eslint.config.js file:

import { FlatCompat } from "@eslint/eslintrc";
import js from "@eslint/js";
import path from "path";
import { fileURLToPath } from "url";

// mimic CommonJS variables -- not needed if using CommonJS
const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

const compat = new FlatCompat({
    baseDirectory: __dirname,                  // optional; default: process.cwd()
    resolvePluginsRelativeTo: __dirname,       // optional
    recommendedConfig: js.configs.recommended, // optional unless you're using "eslint:recommended"
    allConfig: js.configs.all,                 // optional unless you're using "eslint:all"
});

export default [

    // mimic ESLintRC-style extends
    ...compat.extends("standard", "example", "plugin:react/recommended"),

    // mimic environments
    ...compat.env({
        es2020: true,
        node: true
    }),

    // mimic plugins
    ...compat.plugins("jsx-a11y", "react"),

    // translate an entire config
    ...compat.config({
        plugins: ["jsx-a11y", "react"],
        extends: "standard",
        env: {
            es2020: true,
            node: true
        },
        rules: {
            semi: "error"
        }
    })
];

Usage (CommonJS)

Using FlatCompat in CommonJS files is similar to ESM, but you'll use require() and module.exports instead of import and export. Here's how you use it inside of your eslint.config.js CommonJS file:

const { FlatCompat } = require("@eslint/eslintrc");
const js = require("@eslint/js");

const compat = new FlatCompat({
    baseDirectory: __dirname,                  // optional; default: process.cwd()
    resolvePluginsRelativeTo: __dirname,       // optional
    recommendedConfig: js.configs.recommended, // optional unless using "eslint:recommended"
    allConfig: js.configs.all,                 // optional unless using "eslint:all"
});

module.exports = [

    // mimic ESLintRC-style extends
    ...compat.extends("standard", "example", "plugin:react/recommended"),

    // mimic environments
    ...compat.env({
        es2020: true,
        node: true
    }),

    // mimic plugins
    ...compat.plugins("jsx-a11y", "react"),

    // translate an entire config
    ...compat.config({
        plugins: ["jsx-a11y", "react"],
        extends: "standard",
        env: {
            es2020: true,
            node: true
        },
        rules: {
            semi: "error"
        }
    })
];

Troubleshooting

TypeError: Missing parameter 'recommendedConfig' in FlatCompat constructor

The recommendedConfig option is required when any config uses eslint:recommended, including any config in an extends clause. To fix this, follow the example above using @eslint/js to provide the eslint:recommended config.

TypeError: Missing parameter 'allConfig' in FlatCompat constructor

The allConfig option is required when any config uses eslint:all, including any config in an extends clause. To fix this, follow the example above using @eslint/js to provide the eslint:all config.

License

MIT License