index.js

'use strict';

module.exports = {
  extends: 'eslint:recommended',
  env: { es2020: true },
  plugins: ['import'],
  rules: {
    'array-callback-return': 'error',
    'block-scoped-var': 'error',
    'camelcase': ['error', { properties: 'never' }],
    'consistent-return': 'error',
    'curly': ['error', 'multi-line'],
    'default-case': ['error', { commentPattern: '^no default$' }],
    'dot-notation': ['error', { allowKeywords: true }],
    'eqeqeq': ['error', 'allow-null'],
    'guard-for-in': 'error',

    'import/export': 'error',
    'import/imports-first': ['error', 'absolute-first'],
    'import/newline-after-import': 'error',
    'import/no-amd': 'error',
    'import/no-duplicates': 'error',
    'import/no-extraneous-dependencies': [
      'error',
      {
        devDependencies: [
          '**/*.test.js',
          '**/scripts/**',
          '**/test/**',
          '**/tests/**',
          'prettier.config.js',
        ],
      },
    ],
    'import/no-mutable-exports': 'error',
    'import/no-named-as-default': 'error',
    'import/no-named-as-default-member': 'error',
    'import/no-unresolved': ['error', { commonjs: true }],
    'import/prefer-default-export': 'error',

    'new-cap': ['error', { newIsCap: true }],
    'no-array-constructor': 'error',
    'no-caller': 'error',
    'no-confusing-arrow': ['error', { allowParens: false }],
    'no-console': 'error',
    'no-duplicate-imports': 'error',
    'no-else-return': 'error',
    'no-empty-function': ['error', { allow: ['arrowFunctions', 'functions', 'methods'] }],
    'no-eval': 'error',
    'no-extra-bind': 'error',
    'no-extra-label': 'error',
    'no-extra-semi': 'off', // Handled by Prettier
    'no-implied-eval': 'error',
    'no-iterator': 'error',
    'no-label-var': 'error',
    'no-lone-blocks': 'error',
    'no-lonely-if': 'error',
    'no-loop-func': 'error',
    'no-mixed-spaces-and-tabs': 'off', // Handled by Prettier
    'no-multi-str': 'error',
    'no-nested-ternary': 'error',
    'no-new': 'error',
    'no-new-func': 'error',
    'no-new-object': 'error',
    'no-new-require': 'error',
    'no-new-wrappers': 'error',
    'no-octal-escape': 'error',
    'no-proto': 'error',
    'no-restricted-syntax': ['error', 'DebuggerStatement', 'ForInStatement', 'WithStatement'],
    'no-return-assign': 'error',
    'no-script-url': 'error',
    'no-self-compare': 'error',
    'no-sequences': 'error',
    'no-shadow': 'error',
    'no-throw-literal': 'error',
    'no-undef-init': 'error',
    'no-unexpected-multiline': 'off', // Handled by Prettier
    'no-unneeded-ternary': ['error', { defaultAssignment: false }],
    'no-unused-expressions': ['error'],
    'no-unused-vars': ['error', { vars: 'local', args: 'after-used' }],
    'no-useless-computed-key': 'error',
    'no-useless-concat': 'error',
    'no-useless-constructor': 'error',
    'no-useless-rename': [
      'error',
      { ignoreDestructuring: false, ignoreImport: false, ignoreExport: false },
    ],
    'no-var': 'error',
    'no-void': 'error',
    'object-shorthand': ['error', 'always', { ignoreConstructors: false, avoidQuotes: true }],
    'one-var': ['error', 'never'],
    'operator-assignment': ['error', 'always'],
    'quotes': ['error', 'single', { avoidEscape: true }],
    'prefer-arrow-callback': ['error', { allowNamedFunctions: false, allowUnboundThis: true }],
    'prefer-const': ['error', { destructuring: 'any', ignoreReadBeforeAssign: true }],
    'prefer-rest-params': 'error',
    'prefer-spread': 'error',
    'prefer-template': 'error',
    'radix': 'error',
    'require-atomic-updates': 'off', // Reports false positives: https://github.com/eslint/eslint/issues/11899
    'vars-on-top': 'error',
    'spaced-comment': ['error', 'always', { exceptions: ['-', '+'], markers: ['=', '!'] }],
    'strict': ['error', 'safe'],
    'yoda': 'error',
  },
  overrides: [
    {
      files: ['**/*.mjs'],
      parserOptions: { sourceType: 'module' },
    },
    {
      files: ['**/*.test.js', '**/test/**'],
      env: { mocha: true, jest: true },
      rules: {
        'no-unused-expressions': 'off', // Prevent errors on expect's e.g.: expect(foo).to.be.something
      },
    },
    { files: ['jest.setupEnvironment.js'], env: { jest: true } },
  ],
};