Agent skill

eslint-prettier-config

Configures ESLint and Prettier for consistent code quality with TypeScript, React, and modern best practices. Use when users request "ESLint setup", "Prettier config", "linting configuration", "code formatting", or "lint rules".

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SKILL.md

ESLint & Prettier Configuration

Setup consistent code quality and formatting with ESLint and Prettier.

Core Workflow

  1. Install dependencies: ESLint, Prettier, plugins
  2. Configure ESLint: Rules and extends
  3. Configure Prettier: Formatting options
  4. Integrate tools: ESLint + Prettier
  5. Setup scripts: Lint and format commands
  6. Add hooks: Pre-commit validation

ESLint Flat Config (v9+)

typescript
// eslint.config.mjs
import js from '@eslint/js';
import typescript from '@typescript-eslint/eslint-plugin';
import tsParser from '@typescript-eslint/parser';
import react from 'eslint-plugin-react';
import reactHooks from 'eslint-plugin-react-hooks';
import reactRefresh from 'eslint-plugin-react-refresh';
import importPlugin from 'eslint-plugin-import';
import prettier from 'eslint-config-prettier';

export default [
  // Ignore patterns
  {
    ignores: [
      '**/node_modules/**',
      '**/dist/**',
      '**/build/**',
      '**/.next/**',
      '**/coverage/**',
      '**/*.config.js',
      '**/*.config.mjs',
    ],
  },

  // Base JavaScript config
  js.configs.recommended,

  // TypeScript files
  {
    files: ['**/*.ts', '**/*.tsx'],
    languageOptions: {
      parser: tsParser,
      parserOptions: {
        ecmaVersion: 'latest',
        sourceType: 'module',
        ecmaFeatures: {
          jsx: true,
        },
        project: './tsconfig.json',
      },
    },
    plugins: {
      '@typescript-eslint': typescript,
      'import': importPlugin,
    },
    rules: {
      // TypeScript rules
      ...typescript.configs.recommended.rules,
      '@typescript-eslint/no-unused-vars': ['error', {
        argsIgnorePattern: '^_',
        varsIgnorePattern: '^_',
      }],
      '@typescript-eslint/no-explicit-any': 'warn',
      '@typescript-eslint/explicit-function-return-type': 'off',
      '@typescript-eslint/explicit-module-boundary-types': 'off',
      '@typescript-eslint/no-non-null-assertion': 'warn',
      '@typescript-eslint/consistent-type-imports': ['error', {
        prefer: 'type-imports',
        fixStyle: 'inline-type-imports',
      }],

      // Import rules
      'import/order': ['error', {
        groups: [
          'builtin',
          'external',
          'internal',
          ['parent', 'sibling'],
          'index',
          'type',
        ],
        'newlines-between': 'always',
        alphabetize: { order: 'asc', caseInsensitive: true },
      }],
      'import/no-duplicates': 'error',
    },
  },

  // React files
  {
    files: ['**/*.tsx', '**/*.jsx'],
    plugins: {
      'react': react,
      'react-hooks': reactHooks,
      'react-refresh': reactRefresh,
    },
    settings: {
      react: {
        version: 'detect',
      },
    },
    rules: {
      ...react.configs.recommended.rules,
      ...reactHooks.configs.recommended.rules,
      'react/react-in-jsx-scope': 'off',
      'react/prop-types': 'off',
      'react/jsx-uses-react': 'off',
      'react/jsx-no-target-blank': 'error',
      'react/self-closing-comp': 'error',
      'react/jsx-curly-brace-presence': ['error', {
        props: 'never',
        children: 'never',
      }],
      'react-hooks/rules-of-hooks': 'error',
      'react-hooks/exhaustive-deps': 'warn',
      'react-refresh/only-export-components': ['warn', {
        allowConstantExport: true,
      }],
    },
  },

  // Test files
  {
    files: ['**/*.test.ts', '**/*.test.tsx', '**/*.spec.ts', '**/*.spec.tsx'],
    rules: {
      '@typescript-eslint/no-explicit-any': 'off',
      '@typescript-eslint/no-non-null-assertion': 'off',
    },
  },

  // Disable rules that conflict with Prettier
  prettier,
];

ESLint Legacy Config (.eslintrc)

json
// .eslintrc.json
{
  "root": true,
  "env": {
    "browser": true,
    "es2022": true,
    "node": true
  },
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:@typescript-eslint/recommended-type-checked",
    "plugin:react/recommended",
    "plugin:react-hooks/recommended",
    "plugin:import/recommended",
    "plugin:import/typescript",
    "plugin:jsx-a11y/recommended",
    "prettier"
  ],
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "ecmaVersion": "latest",
    "sourceType": "module",
    "ecmaFeatures": {
      "jsx": true
    },
    "project": ["./tsconfig.json"]
  },
  "plugins": [
    "@typescript-eslint",
    "react",
    "react-hooks",
    "import",
    "jsx-a11y"
  ],
  "settings": {
    "react": {
      "version": "detect"
    },
    "import/resolver": {
      "typescript": {
        "alwaysTryTypes": true
      }
    }
  },
  "rules": {
    // TypeScript
    "@typescript-eslint/no-unused-vars": ["error", {
      "argsIgnorePattern": "^_",
      "varsIgnorePattern": "^_"
    }],
    "@typescript-eslint/consistent-type-imports": ["error", {
      "prefer": "type-imports",
      "fixStyle": "inline-type-imports"
    }],
    "@typescript-eslint/no-explicit-any": "warn",
    "@typescript-eslint/no-floating-promises": "error",
    "@typescript-eslint/await-thenable": "error",

    // React
    "react/react-in-jsx-scope": "off",
    "react/prop-types": "off",
    "react/self-closing-comp": "error",

    // Imports
    "import/order": ["error", {
      "groups": ["builtin", "external", "internal", "parent", "sibling", "index", "type"],
      "newlines-between": "always",
      "alphabetize": { "order": "asc" }
    }],
    "import/no-duplicates": "error",
    "import/no-unresolved": "error",

    // General
    "no-console": ["warn", { "allow": ["warn", "error"] }],
    "prefer-const": "error",
    "no-var": "error"
  },
  "overrides": [
    {
      "files": ["*.test.ts", "*.test.tsx", "*.spec.ts", "*.spec.tsx"],
      "rules": {
        "@typescript-eslint/no-explicit-any": "off",
        "@typescript-eslint/no-floating-promises": "off"
      }
    }
  ],
  "ignorePatterns": [
    "node_modules",
    "dist",
    "build",
    ".next",
    "coverage"
  ]
}

Prettier Configuration

json
// .prettierrc
{
  "semi": true,
  "singleQuote": true,
  "trailingComma": "es5",
  "tabWidth": 2,
  "useTabs": false,
  "printWidth": 100,
  "bracketSpacing": true,
  "bracketSameLine": false,
  "arrowParens": "always",
  "endOfLine": "lf",
  "quoteProps": "as-needed",
  "jsxSingleQuote": false,
  "proseWrap": "preserve",
  "htmlWhitespaceSensitivity": "css",
  "embeddedLanguageFormatting": "auto"
}
json
// .prettierignore
node_modules
dist
build
.next
coverage
*.min.js
*.min.css
pnpm-lock.yaml
package-lock.json
yarn.lock

Package Dependencies

json
// package.json (partial)
{
  "scripts": {
    "lint": "eslint . --ext .ts,.tsx --max-warnings 0",
    "lint:fix": "eslint . --ext .ts,.tsx --fix",
    "format": "prettier --write \"**/*.{ts,tsx,json,md,css}\"",
    "format:check": "prettier --check \"**/*.{ts,tsx,json,md,css}\"",
    "typecheck": "tsc --noEmit",
    "check": "npm run typecheck && npm run lint && npm run format:check"
  },
  "devDependencies": {
    "@eslint/js": "^9.0.0",
    "@typescript-eslint/eslint-plugin": "^7.0.0",
    "@typescript-eslint/parser": "^7.0.0",
    "eslint": "^9.0.0",
    "eslint-config-prettier": "^9.1.0",
    "eslint-import-resolver-typescript": "^3.6.0",
    "eslint-plugin-import": "^2.29.0",
    "eslint-plugin-jsx-a11y": "^6.8.0",
    "eslint-plugin-react": "^7.33.0",
    "eslint-plugin-react-hooks": "^4.6.0",
    "eslint-plugin-react-refresh": "^0.4.0",
    "prettier": "^3.2.0",
    "typescript": "^5.3.0"
  }
}

Git Hooks with Husky

bash
# Install Husky
npm install -D husky lint-staged
npx husky init
json
// package.json
{
  "lint-staged": {
    "*.{ts,tsx}": [
      "eslint --fix --max-warnings 0",
      "prettier --write"
    ],
    "*.{json,md,css,scss}": [
      "prettier --write"
    ]
  }
}
bash
# .husky/pre-commit
npx lint-staged
bash
# .husky/commit-msg
npx commitlint --edit $1

Commitlint Configuration

javascript
// commitlint.config.js
module.exports = {
  extends: ['@commitlint/config-conventional'],
  rules: {
    'type-enum': [
      2,
      'always',
      [
        'feat',     // New feature
        'fix',      // Bug fix
        'docs',     // Documentation
        'style',    // Formatting
        'refactor', // Code restructuring
        'perf',     // Performance
        'test',     // Tests
        'build',    // Build system
        'ci',       // CI configuration
        'chore',    // Maintenance
        'revert',   // Revert changes
      ],
    ],
    'subject-case': [2, 'always', 'lower-case'],
    'subject-max-length': [2, 'always', 72],
    'body-max-line-length': [2, 'always', 100],
  },
};

VS Code Integration

json
// .vscode/settings.json
{
  "editor.formatOnSave": true,
  "editor.defaultFormatter": "esbenp.prettier-vscode",
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": "explicit",
    "source.organizeImports": "never"
  },
  "[typescript]": {
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[typescriptreact]": {
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[json]": {
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "eslint.validate": [
    "javascript",
    "javascriptreact",
    "typescript",
    "typescriptreact"
  ],
  "typescript.preferences.importModuleSpecifier": "relative",
  "typescript.suggest.autoImports": true
}
json
// .vscode/extensions.json
{
  "recommendations": [
    "dbaeumer.vscode-eslint",
    "esbenp.prettier-vscode",
    "bradlc.vscode-tailwindcss",
    "streetsidesoftware.code-spell-checker"
  ]
}

Next.js Specific

javascript
// .eslintrc.js (Next.js)
module.exports = {
  extends: [
    'next/core-web-vitals',
    'plugin:@typescript-eslint/recommended',
    'prettier',
  ],
  parser: '@typescript-eslint/parser',
  plugins: ['@typescript-eslint'],
  rules: {
    '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
    '@typescript-eslint/consistent-type-imports': 'error',
    'import/order': ['error', {
      groups: ['builtin', 'external', 'internal', 'parent', 'sibling', 'index'],
      'newlines-between': 'always',
    }],
  },
};

Node.js/API Specific

javascript
// eslint.config.mjs (Node.js API)
import js from '@eslint/js';
import typescript from '@typescript-eslint/eslint-plugin';
import tsParser from '@typescript-eslint/parser';
import nodePlugin from 'eslint-plugin-n';
import prettier from 'eslint-config-prettier';

export default [
  js.configs.recommended,
  {
    files: ['**/*.ts'],
    languageOptions: {
      parser: tsParser,
      parserOptions: {
        project: './tsconfig.json',
      },
    },
    plugins: {
      '@typescript-eslint': typescript,
      'n': nodePlugin,
    },
    rules: {
      ...typescript.configs.recommended.rules,
      'n/no-process-exit': 'error',
      'n/no-unsupported-features/es-syntax': 'off',
      '@typescript-eslint/no-floating-promises': 'error',
      '@typescript-eslint/require-await': 'error',
    },
  },
  prettier,
];

Custom Rules Examples

typescript
// Custom ESLint rule example (eslint-plugin-custom/no-direct-env.js)
module.exports = {
  meta: {
    type: 'problem',
    docs: {
      description: 'Disallow direct process.env access',
    },
    messages: {
      noDirectEnv: 'Use config module instead of direct process.env access',
    },
  },
  create(context) {
    return {
      MemberExpression(node) {
        if (
          node.object.type === 'MemberExpression' &&
          node.object.object.name === 'process' &&
          node.object.property.name === 'env'
        ) {
          context.report({
            node,
            messageId: 'noDirectEnv',
          });
        }
      },
    };
  },
};

Best Practices

  1. Extend carefully: Order matters in extends
  2. Use type-checking: Enable type-aware rules
  3. Consistent imports: Enforce import ordering
  4. Prettier last: Always extend prettier last
  5. Auto-fix on save: Configure VS Code
  6. Pre-commit hooks: Validate before commit
  7. CI validation: Run lint in CI pipeline
  8. Progressive adoption: Start with warnings

Output Checklist

Every ESLint/Prettier setup should include:

  • ESLint configuration (flat or legacy)
  • TypeScript-ESLint integration
  • React/React Hooks rules
  • Import ordering rules
  • Prettier configuration
  • ESLint-Prettier integration
  • VS Code settings
  • Husky pre-commit hooks
  • lint-staged configuration
  • CI lint validation
  • Ignore patterns
  • npm scripts for lint/format

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