.eslintrc.js

module.exports = {
  env: {
    es6: true,
    node: true,
    browser: true,
    jest: true,
  },
  extends: [
    'airbnb',
    'plugin:@typescript-eslint/recommended',
    'plugin:@typescript-eslint/eslint-recommended',
    'prettier',
    'prettier/@typescript-eslint',
    'plugin:prettier/recommended',
  ],
  parser: '@typescript-eslint/parser',
  plugins: ['@typescript-eslint', 'prettier'],
  parserOptions: {
    ecmaVersion: 2018,
    sourceType: 'module',
    ecmaFeatures: {
      impliedStrict: true,
      jsx: true,
    },
  },
  rules: {
    // Max line-length is 120.
    'max-len': [
      'error',
      {
        code: 120,
        ignoreUrls: true,
      },
    ],

    // Disable multiline expressions and lines that start with `[` or `(`.
    'no-unexpected-multiline': 'error',

    // Allow setting square bracket notation.
    'dot-notation': 'off',

    // Allow devDependencies for production code (especially tests).
    'import/no-extraneous-dependencies': 'off',

    // Override some JSX/React rules.
    'jsx-a11y/anchor-is-valid': 'off',
    'react/jsx-closing-tag-location': 'off',
    'react/jsx-curly-brace-presence': 'off',
    'react/jsx-filename-extension': [
      'error',
      {
        extensions: ['.js', '.jsx', '.tsx'],
      },
    ],
    'react/jsx-one-expression-per-line': 'off',
    'react/jsx-props-no-spreading': 'off',
    'react/prop-types': 'off',
    'react/static-property-placement': 'off',
    '@typescript-eslint/explicit-function-return-type': ['off'],
    'spaced-comment': [
      'error',
      'always',
      {
        markers: ['/'],
      },
    ],
    'jsx-a11y/label-has-for': [
      2,
      {
        required: {
          every: ['id'],
        },
      },
    ],
  },
  settings: {
    'import/resolver': {
      node: {
        paths: ['src'],
        extensions: ['.js', '.jsx', '.ts', '.tsx'],
      },
      typescript: {},
    },
    'import/extensions': ['.js', '.mjs', '.jsx', '.ts', '.tsx'],
  },
  overrides: [
    {
      files: ['**/*.ts', '**/*.tsx'],
      parserOptions: {
        ecmaVersion: 2018,
        sourceType: 'module',

        // typescript-eslint specific options
        warnOnUnsupportedTypeScriptVersion: true,
      },
      rules: {
        // Allow `.ts` and `.tsx` extensions to be omitted
        'import/extensions': [
          'error',
          'ignorePackages',
          {
            js: 'never',
            mjs: 'never',
            jsx: 'never',
            ts: 'never',
            tsx: 'never',
          },
        ],

        // Allow unused variables that starts with, or is `_`
        '@typescript-eslint/no-unused-vars': [
          'warn',
          {
            argsIgnorePattern: '^_',
            varsIgnorePattern: '^_',
          },
        ],

        // Allow camelcase.
        '@typescript-eslint/camelcase': 'off',

        // No need to add return type for functions, it's inferred already.
        '@typescript-eslint/explicit-function-return-type': ['off'],
      },
    },
    {
      files: ['.eslintrc.js'],
      parserOptions: {
        sourceType: 'script',
      },
      env: {
        node: true,
      },
    },
  ],
};