.eslintrc.json

{
  // JS Files
  "root": true,
  "env": {
    "atomtest": true,
    "es6": true,
    "node": true,
    "browser": true,
    "jasmine": true
  },
  "globals": { "atom": "readonly"},
  "parser": "babel-eslint",
  "parserOptions": {
    "ecmaFeatures": { "jsx": true },
    "ecmaVersion": 2018,
    "sourceType": "module"
  },
  "plugins": ["only-warn"],
  "extends": ["eslint:recommended"],
  "ignorePatterns": ["lib/", "node_modules/"],
  "overrides": [
    { // Bundled node version with atom has an old ESLint
      // TypeScript files
      "files": ["**/*.ts", "**/*.tsx"],
      "parser": "@typescript-eslint/parser",
      "parserOptions": {
        "ecmaFeatures": { "jsx": true },
        "ecmaVersion": 2018,
        "sourceType": "module"
      },
      "plugins": ["@typescript-eslint", "only-warn"],
      "extends": [
        "eslint:recommended",
        "plugin:@typescript-eslint/eslint-recommended",
        "plugin:@typescript-eslint/recommended"
      ],
      "rules": {
        "@typescript-eslint/explicit-function-return-type": "off",
        "@typescript-eslint/camelcase": "off",
        "@typescript-eslint/no-use-before-define": "off",
        "@typescript-eslint/member-delimiter-style": "off"
      }
    },
    {
      // CoffeeScript files
      "files": ["**/*.coffee"],
      "parser": "eslint-plugin-coffee",
      "parserOptions": {
        "ecmaFeatures": { "jsx": true },
        "ecmaVersion": 2018,
        "sourceType": "module"
      },
      "plugins": ["coffee", "only-warn"],
      "extends": ["plugin:coffee/eslint-recommended"]
    },
    {
      // JSON files
      "files": ["*.json"],
      "plugins": ["json"],
      "extends": ["plugin:json/recommended"],
      "rules": {
        "json/*": ["error", {"allowComments": true}]
      }
    }
  ]
}