.eslintrc.js

/**
 * ESLint Configuration - Enterprise Grade
 *
 * Strict rules for production-quality code.
 * All warnings are errors in CI (--max-warnings 0).
 */
module.exports = {
  env: {
    browser: true,
    es2021: true,
    node: true,
  },
  extends: ['eslint:recommended'],
  parserOptions: {
    ecmaVersion: 'latest',
    sourceType: 'module',
  },
  rules: {
    // ==================== ERRORS (Must Fix) ====================

    // Variables
    'no-unused-vars': ['error', { argsIgnorePattern: '^_', varsIgnorePattern: '^_' }],
    'no-undef': 'error',
    'no-use-before-define': ['error', { functions: false, classes: true }],
    'no-shadow': 'error',
    'no-redeclare': 'error',

    // Best Practices
    eqeqeq: ['error', 'always'],
    curly: ['error', 'all'],
    'no-eval': 'error',
    'no-implied-eval': 'error',
    'no-extend-native': 'error',
    'no-extra-bind': 'error',
    'no-floating-decimal': 'error',
    'no-implicit-coercion': 'error',
    'no-invalid-this': 'error',
    'no-lone-blocks': 'error',
    'no-multi-spaces': 'error',
    'no-new': 'error',
    'no-new-func': 'error',
    'no-new-wrappers': 'error',
    'no-return-assign': 'error',
    'no-self-compare': 'error',
    'no-sequences': 'error',
    'no-throw-literal': 'error',
    'no-useless-call': 'error',
    'no-useless-concat': 'error',
    'no-useless-return': 'error',
    'prefer-promise-reject-errors': 'error',
    radix: 'error',

    // ES6+
    'prefer-const': 'error',
    'no-var': 'error',
    'prefer-template': 'error',
    'prefer-spread': 'error',
    'prefer-rest-params': 'error',
    'no-duplicate-imports': 'error',
    'no-useless-constructor': 'error',
    'no-useless-rename': 'error',
    'object-shorthand': ['error', 'always'],
    'prefer-arrow-callback': 'error',
    'arrow-body-style': ['error', 'as-needed'],

    // ==================== WARNINGS (Fix Before PR) ====================

    // Console logging (allowed: warn, error, log for debugging)
    'no-console': ['warn', { allow: ['warn', 'error', 'log'] }],

    // Complexity
    complexity: ['warn', { max: 15 }],
    'max-depth': ['warn', { max: 4 }],
    'max-lines-per-function': ['warn', { max: 100, skipBlankLines: true, skipComments: true }],
    'max-params': ['warn', { max: 5 }],
    'max-nested-callbacks': ['warn', { max: 4 }],

    // Documentation
    'require-jsdoc': [
      'warn',
      {
        require: {
          FunctionDeclaration: true,
          MethodDefinition: true,
          ClassDeclaration: true,
        },
      },
    ],
    'valid-jsdoc': [
      'warn',
      {
        requireReturn: false,
        requireParamDescription: false,
        requireReturnDescription: false,
      },
    ],

    // Style (enforced by Prettier, but ESLint catches some)
    'no-trailing-spaces': 'error',
    'no-multiple-empty-lines': ['error', { max: 2, maxEOF: 1 }],
    'eol-last': ['error', 'always'],
    'comma-dangle': ['error', 'always-multiline'],
    semi: ['error', 'always'],
    quotes: ['error', 'single', { avoidEscape: true, allowTemplateLiterals: true }],
  },

  overrides: [
    // Test files - relaxed rules
    {
      files: ['**/*.test.js', '**/*.spec.js', 'tests/**/*.js'],
      env: {
        jest: true,
      },
      rules: {
        'no-magic-numbers': 'off',
        'max-lines-per-function': 'off',
        'require-jsdoc': 'off',
        'valid-jsdoc': 'off',
        'no-console': 'off',
      },
    },
    // Config files - relaxed rules
    {
      files: ['*.config.js', '.eslintrc.js', 'vite.config.js', 'vitest.config.js'],
      rules: {
        'no-magic-numbers': 'off',
        'require-jsdoc': 'off',
        'valid-jsdoc': 'off',
      },
    },
  ],
};