.eslintrc.js

module.exports = {
  env: {
    node: true,
    browser: true,
    es2020: true,
  },
  extends: [
    'eslint:recommended',
  ],
  plugins: [
    'import',
    'no-floating-promise',
    'sort-class-members',
  ],
  settings: {
    react: {
      version: 'detect',
    },
  },
  rules: {
    'linebreak-style': [ 'error', 'unix' ],

    // Style
    'quotes': [ 'error', 'single', { avoidEscape: true } ],

    'no-unused-vars': [
      'error',
      { argsIgnorePattern: '^_' },
    ],

    // ensures clean diffs, see https://medium.com/@nikgraf/why-you-should-enforce-dangling-commas-for-multiline-statements-d034c98e36f8
    'comma-dangle': [ 'error', 'always-multiline' ],

    // Require all imported dependencies are actually declared in package.json
    'import/no-extraneous-dependencies': [
      'error',
      {
        optionalDependencies: false,    // Disallow importing optional dependencies (those shouldn't be in use in the project)
        peerDependencies: false,         // Disallow importing peer dependencies (that aren't also direct dependencies)
      },
    ],

    // Require all imported libraries actually resolve (!!required for import/no-extraneous-dependencies to work!!)
    'import/no-unresolved': [ 'error' ],

    // Require an ordering on all imports
    'import/order': ['warn', {
      groups: ['builtin', 'external'],
      alphabetize: { order: 'asc' },
    }],

    // Cannot import from the same module twice
    'no-duplicate-imports': ['error'],

    // Cannot shadow names
    'no-shadow': ['error'],

    // Required spacing in property declarations (copied from TSLint, defaults are good)
    'key-spacing': ['error'],

    // Require semicolons
    'semi': ['error', 'always'],

    // Don't unnecessarily quote properties
    'quote-props': ['error', 'consistent-as-needed'],

    // No multiple empty lines
    'no-multiple-empty-lines': ['error'],

    // Max line lengths
    'max-len': ['error', {
      code: 120,
      ignoreUrls: true, // Most common reason to disable it
      ignoreStrings: true, // These are not fantastic but necessary for error messages
      ignoreTemplateLiterals: true,
      ignoreComments: true,
      ignoreRegExpLiterals: true,
    }],

    // One of the easiest mistakes to make
    'no-floating-promise/no-floating-promise': 2,

    // Don't leave log statements littering the premises!
    'no-console': ['error'],

    // Useless diff results
    'no-trailing-spaces': ['error'],

    // Must use foo.bar instead of foo['bar'] if possible
    'dot-notation': ['error'],

    // Are you sure | is not a typo for || ?
    'no-bitwise': ['error'],

    // Member ordering
    'sort-class-members/sort-class-members': [2, {
      order: [
        '[static-properties]',
        '[static-methods]',
        '[properties]',
        '[conventional-private-properties]',
        'constructor',
        '[methods]',
        '[conventional-private-methods]',
      ],
    }],
  },
  root: true,
};