hjemmesidekongen/eslint-config

eslint-config

ESLint 9 made flat config the default. Every new project should start with eslint.config.js. Legacy .eslintrc is deprecated and will be removed.

Flat Config Overview

eslint.config.js exports an array of config objects. Each object applies to files matched by its files glob. Objects merge in order — later entries override earlier ones for the same rule.

import js from "@eslint/js";
import globals from "globals";

export default [
  js.configs.recommended,
  { languageOptions: { globals: globals.browser } },
  { rules: { "no-unused-vars": "warn" } },
];

No more extends string references — import config objects directly. No more env — use languageOptions.globals.

Migration from .eslintrc

Key differences: extends → spread config objects, env → languageOptions.globals, parser → languageOptions.parser, parserOptions → languageOptions.parserOptions, plugins → object map (not array), ignorePatterns → top-level ignores array.

Run npx @eslint/migrate-config .eslintrc.js for automated migration. Expect manual cleanup for complex plugin setups.

When to Customize vs Use Presets

Start with a preset (@eslint/js, typescript-eslint, eslint-config-prettier). Customize only when a preset rule conflicts with team conventions or creates false positives in your stack. Disabling rules is a last resort — prefer configuring them.

Key Rules to Know

• no-unused-vars — set to ["error", { argsIgnorePattern: "^_" }] to allow intentional ignores
• no-console — warn in app code, disabled in scripts and CLI tools
• eqeqeq — always error; == null checks are the only safe exception
• @typescript-eslint/no-explicit-any — warn, not error; some integration seams need it See references/process.md for flat config structure, TypeScript setup, custom rule creation, plugin setup, shared configs, file-specific overrides, ignores, Prettier integration, performance, CI setup, and anti-patterns.