.eslintrc.js

module.exports = {
  parserOptions: {
    ecmaVersion: 2018,
    sourceType: 'module',
  },
  env: {
    browser: true,
  },
  plugins: ['svelte3', 'prettier'],
  extends: ['eslint:recommended', 'prettier'],
  overrides: [
    {
      files: ['*.svelte'],
      processor: 'svelte3/svelte3',
    },
  ],
  rules: {
    // Errors
    'no-console': 'warn',
    // Best practices
    'array-callback-return': ['error', { allowImplicit: true }],
    'block-scoped-var': 'error',
    'consistent-return': 'error',
    curly: ['error', 'multi-line'],
    'default-param-last': 'error',
    'dot-notation': ['error', { allowKeywords: true }],
    eqeqeq: ['error', 'always', { null: 'ignore' }],
    'guard-for-in': 'error',
    'max-classes-per-file': ['error', 1],
    'no-alert': 'error',
    'no-caller': 'error',
    'no-eval': 'error',
    'no-extend-native': 'error',
    'no-extra-bind': 'error',
    'no-extra-label': 'error',
    'no-floating-decimal': 'error',
    'no-implicit-coercion': [
      'off',
      {
        boolean: false,
        number: true,
        string: true,
        allow: [],
      },
    ],
    'no-iterator': 'error',
    'no-labels': ['error', { allowLoop: false, allowSwitch: false }],
    'no-lone-blocks': 'error',
    'no-loop-func': 'error',
    'no-multi-str': 'error',
    'no-new': 'error',
    'no-new-func': 'error',
    'no-new-wrappers': 'error',
    'no-param-reassign': [
      'error',
      {
        props: true,
        ignorePropertyModificationsFor: [
          'acc', // for reduce accumulators
          'accumulator', // for reduce accumulators
          'e', // for e.returnvalue
          'ctx', // for Koa routing
          'context', // for Koa routing
          'req', // for Express requests
          'request', // for Express requests
          'res', // for Express responses
          'response', // for Express responses
          '$scope', // for Angular 1 scopes
          'staticContext', // for ReactRouter context
        ],
      },
    ],
    'no-proto': 'error',
    'no-redeclare': 'error',
    'no-return-assign': ['error', 'always'],
    'no-return-await': 'error',
    'no-script-url': 'error',
    'no-self-assign': [
      'error',
      {
        props: true,
      },
    ],
    'no-self-compare': 'error',
    'no-sequences': 'error',
    'no-unused-expressions': [
      'error',
      {
        allowShortCircuit: false,
        allowTernary: false,
        allowTaggedTemplates: false,
      },
    ],
    'no-useless-concat': 'error',
    'no-useless-return': 'error',
    'prefer-promise-reject-errors': ['error', { allowEmptyReject: true }],
    'vars-on-top': 'error',
    // Variables:
    'no-label-var': 'error',
    'no-shadow': 'off',
    'no-shadow-restricted-names': 'error',
    'no-undef-init': 'error',
    'no-unused-vars': 'off',
    'no-use-before-define': 'off',
    'no-redeclare': 'off',
    // Style
    semi: ['error', 'always'],
    // ES6
    'no-var': 'error',
  },
  ignorePatterns: [
    'node_modules/*',
    'dist/*',
    'types',
    '.prettierrc.js',
    '.eslintrc.js',
    'tailwind.config.js',
  ],
};