eslint

# ESLint — JavaScript and TypeScript Linting ESLint reads your source code, applies a set of rules, and reports problems ranging from stylistic inconsistencies to genuine bugs. It catches unused variables, missing return statements, inconsistent naming, accessibility violations, and hundreds of other issues that slip past even careful code review. This skill covers ESLint 9+ with the modern flat config format. If you're starting a new project or migrating from the legacy `.eslintrc` format, flat config is the way forward. ## Installing ESLint ESLint 9 ships as a single package. TypeScript and React support come from companion plugins. ```bash # Install ESLint and common plugins for a TypeScript React project npm install --save-dev eslint @eslint/js typescript-eslint eslint-plugin-react eslint-plugin-react-hooks ``` ## Flat Config Basics The flat config lives in `eslint.config.js` (or `.mjs`, `.ts`) at your project root. Instead of deeply nested JSON with `extends` and `overrides`, flat config uses an array of configuration objects. Each object applies to files matching its `files` glob pattern. ```javascript // eslint.config.js — Flat config for a TypeScript project import js from '@eslint/js'; import tseslint from 'typescript-eslint'; export default [ // Base JavaScript recommended rules js.configs.recommended, // TypeScript recommended rules (type-aware) ...tseslint.configs.recommended, // Custom configuration for source files { files: ['src/**/*....