.eslintrc.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

'use strict';

// Inspired by https://github.com/airbnb/javascript but less opinionated.

// We use eslint-loader so even warnings are very visible.
// This is why we only use "WARNING" level for potential errors,
// and we don't use "ERROR" level at all.

// In the future, we might create a separate list of rules for production.
// It would probably be more strict.

module.exports = {
  root: true,

  parser: 'babel-eslint',

  plugins: ['markdown', 'import', 'jsx-a11y', 'react', 'prettier'],

  extends: ['prettier', 'prettier/react'],

  env: {
    browser: true,
    commonjs: true,
    es6: true,
    jest: true,
    node: true,
  },

  parserOptions: {
    ecmaVersion: 6,
    sourceType: 'module',
    ecmaFeatures: {
      jsx: true,
      generators: true,
      experimentalObjectRestSpread: true,
    },
  },

  settings: {
    'import/ignore': ['node_modules'],
    'import/extensions': ['.js'],
    'import/resolver': {
      node: {
        extensions: ['.js', '.json'],
      },
    },
    react: {
      version: 'detect',
    },
  },

  rules: {
    // http://eslint.org/docs/rules/
    'array-callback-return': 'warn',
    'default-case': ['warn', {commentPattern: '^no default$'}],
    eqeqeq: ['warn', 'allow-null'],
    'no-array-constructor': 'warn',
    'no-caller': 'warn',
    'no-cond-assign': ['warn', 'always'],
    'no-const-assign': 'warn',
    'no-control-regex': 'warn',
    'no-delete-var': 'warn',
    'no-dupe-args': 'warn',
    'no-dupe-class-members': 'warn',
    'no-dupe-keys': 'warn',
    'no-duplicate-case': 'warn',
    'no-empty-character-class': 'warn',
    'no-empty-pattern': 'warn',
    'no-eval': 'warn',
    'no-ex-assign': 'warn',
    'no-extend-native': 'warn',
    'no-extra-bind': 'warn',
    'no-extra-label': 'warn',
    'no-fallthrough': 'warn',
    'no-func-assign': 'warn',
    'no-implied-eval': 'warn',
    'no-invalid-regexp': 'warn',
    'no-iterator': 'warn',
    'no-label-var': 'warn',
    'no-labels': ['warn', {allowLoop: false, allowSwitch: false}],
    'no-lone-blocks': 'warn',
    'no-loop-func': 'warn',
    'no-multi-str': 'warn',
    'no-native-reassign': 'warn',
    'no-negated-in-lhs': 'warn',
    'no-new-func': 'warn',
    'no-new-object': 'warn',
    'no-new-symbol': 'warn',
    'no-new-wrappers': 'warn',
    'no-obj-calls': 'warn',
    'no-octal': 'warn',
    'no-octal-escape': 'warn',
    'no-redeclare': 'warn',
    'no-regex-spaces': 'warn',
    'no-restricted-syntax': ['warn', 'LabeledStatement', 'WithStatement'],
    'no-script-url': 'warn',
    'no-self-assign': 'warn',
    'no-self-compare': 'warn',
    'no-sequences': 'warn',
    'no-shadow-restricted-names': 'warn',
    'no-sparse-arrays': 'warn',
    'no-template-curly-in-string': 'warn',
    'no-this-before-super': 'warn',
    'no-throw-literal': 'warn',
    'no-undef': 'error',
    'no-restricted-globals': ['error', 'event'],
    'no-unexpected-multiline': 'warn',
    'no-unreachable': 'warn',
    'no-unused-expressions': [
      'warn',
      {
        allowShortCircuit: true,
        allowTernary: true,
      },
    ],
    'no-unused-labels': 'warn',
    'no-unused-vars': [
      'warn',
      {
        vars: 'local',
        varsIgnorePattern: '^_',
        args: 'none',
        ignoreRestSiblings: true,
      },
    ],
    'no-use-before-define': ['warn', 'nofunc'],
    'no-useless-computed-key': 'warn',
    'no-useless-concat': 'warn',
    'no-useless-constructor': 'warn',
    'no-useless-escape': 'warn',
    'no-useless-rename': [
      'warn',
      {
        ignoreDestructuring: false,
        ignoreImport: false,
        ignoreExport: false,
      },
    ],
    'no-with': 'warn',
    'operator-assignment': ['warn', 'always'],
    radix: 'warn',
    'require-yield': 'warn',
    strict: ['warn', 'never'],
    'use-isnan': 'warn',
    'valid-typeof': 'warn',
    'no-restricted-properties': [
      'error',
      {
        object: 'require',
        property: 'ensure',
        message:
          'Please use import() instead. More info: https://webpack.js.org/guides/code-splitting-import/#dynamic-import',
      },
      {
        object: 'System',
        property: 'import',
        message:
          'Please use import() instead. More info: https://webpack.js.org/guides/code-splitting-import/#dynamic-import',
      },
    ],

    // https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/

    // TODO: import rules are temporarily disabled because they don't play well
    // with how eslint-loader only checks the file you change. So if module A
    // imports module B, and B is missing a default export, the linter will
    // record this as an issue in module A. Now if you fix module B, the linter
    // will not be aware that it needs to re-lint A as well, so the error
    // will stay until the next restart, which is really confusing.

    // This is probably fixable with a patch to eslint-loader.
    // When file A is saved, we want to invalidate all files that import it
    // *and* that currently have lint errors. This should fix the problem.
    // (As an exception, import/no-webpack-loader-syntax can be enabled already
    // because it doesn't depend on whether the file exists, so this issue
    // doesn't apply to it.)

    // 'import/default': 'warn',
    // 'import/export': 'warn',
    // 'import/named': 'warn',
    // 'import/namespace': 'warn',
    // 'import/no-amd': 'warn',
    // 'import/no-duplicates': 'warn',
    // 'import/no-extraneous-dependencies': 'warn',
    // 'import/no-named-as-default': 'warn',
    // 'import/no-named-as-default-member': 'warn',
    // 'import/no-unresolved': ['warn', { commonjs: true }],
    // We don't support configuring Webpack using import source strings, so this
    // is always an error.
    'import/no-webpack-loader-syntax': 'error',

    // https://github.com/yannickcr/eslint-plugin-react/tree/master/docs/rules
    'react/jsx-no-duplicate-props': ['warn', {ignoreCase: true}],
    'react/jsx-no-undef': 'error',
    'react/jsx-pascal-case': [
      'warn',
      {
        allowAllCaps: true,
        ignore: [],
      },
    ],
    'react/jsx-uses-react': 'warn',
    'react/jsx-uses-vars': 'warn',
    'react/no-danger-with-children': 'warn',
    'react/no-deprecated': 'warn',
    'react/no-direct-mutation-state': 'warn',
    'react/no-is-mounted': 'warn',
    'react/react-in-jsx-scope': 'error',
    'react/require-render-return': 'warn',
    'react/style-prop-object': 'warn',

    // https://github.com/evcohen/eslint-plugin-jsx-a11y/tree/master/docs/rules
    'jsx-a11y/aria-role': 'warn',
    'jsx-a11y/img-redundant-alt': 'warn',
    'jsx-a11y/no-access-key': 'warn',

    'prettier/prettier': [
      'error',
      {
        singleQuote: true,
        trailingComma: 'all',
        jsxBracketSameLine: true,
      },
    ],
  },
};