.eslintrc

{
  "root": true,
  "parserOptions": {
    "ecmaVersion": 6,
    "ecmaFeatures": {
      "jsx": true,
      "experimentalObjectRestSpread": true
    },
    "sourceType": "module"
  },
  "env": {
    "browser": true,
    "node": true,
    "es6": true
  },
  "plugins": ["react"],
  "extends": ["airbnb"],
  "rules": {
    // Copy most recent airbnb-style for max-len rule. eslint we bumped to
    // to take advantage of the `ignoreRegExpLiterals` rule, but airbnb style
    // itself was not bumped because of many new rules that break existing code.
    // Line length is currently a warning to not break old code
    "max-len": ["warn", 100, 2, {
      ignoreUrls: true,
      ignoreComments: false,
      ignoreRegExpLiterals: true,
      ignoreStrings: true,
      ignoreTemplateLiterals: true,
    }],

    // Allow arguments in functions to be unused
    // This allows us to specify that a function will be called with arguments
    // even though we do not need it, e.g. in Promise (resolve, reject),
    // onEvent(event), catch(error), etc.
    "no-unused-vars": ["error", { vars: "local", args: "none" }],

    // Warnings for things that are not easily fixable now
    "react/jsx-filename-extension": "warn",
    "react/prefer-stateless-function": "warn",
    "react/no-array-index-key": "warn",
    "import/prefer-default-export": "warn",

    // This is disallowed for good reasons, but unfortunately too much of our
    // code relies explicitly on this behavior to set properties on an object
    // referred to by an outer function (most notably CodeMirror state)
    "no-param-reassign": "warn",

    // Allow class functions to not use `this`
    "class-methods-use-this": "warn",

    // Allow unary operators in the afterthought of a for loop
    // Not sure why Airbnb disallows this
    "no-plusplus": ["error", { "allowForLoopAfterthoughts": true }],

    // Allow non-interactive DOM elements to have interactive handlers. This is
    // now a warning as a reminder that another element might be better, but
    // we will not enforce it.
    "jsx-a11y/no-static-element-interactions": "warn",

    // Ignores comma-dangle for function arguments, as it breaks parsing and it
    // behaves strangely if arguments are JSX
    "comma-dangle": ["error", {
      arrays: "always-multiline",
      objects: "always-multiline",
      imports: "always-multiline",
      exports: "always-multiline",
      functions: "ignore",
    }],

    // Remove `ForOfSyntax`. Some things are iterators.
    'no-restricted-syntax': [
      'error',
      'ForInStatement',
      'LabeledStatement',
      'WithStatement',
    ],

    // Allow optional dependencies (like electron)
    // Do not override devDependency array (so this is copied)
    'import/no-extraneous-dependencies': ['error', {
      devDependencies: [
        'test/**', // tape, common npm pattern
        'tests/**', // also common npm pattern
        'spec/**', // mocha, rspec-like pattern
        '**/__tests__/**', // jest pattern
        'test.js', // repos with a single test file
        'test-*.js', // repos with multiple top-level test files
        '**/*.test.js', // tests where the extension denotes that it is a test
        '**/*.spec.js', // tests where the extension denotes that it is a test
        '**/webpack.config.js', // webpack config
        '**/webpack.config.*.js', // webpack config
        '**/rollup.config.js', // rollup config
        '**/rollup.config.*.js', // rollup config
        '**/gulpfile.js', // gulp config
        '**/gulpfile.*.js', // gulp config
        '**/Gruntfile', // grunt config
      ],
      optionalDependencies: true,
    }],
  }
}