.eslintrc.json

{
    "extends": [
        "airbnb-base"
    ],

    "env": {
      "browser": true,
      "es2017": true
    },

    "parserOptions": {
        "ecmaVersion": 2017,
        "sourceType": "module"
    },

    "overrides": [
        {
            "files": ["*.spec.js"],
            "env": {
                "mocha": true
            },
            "globals": {
                "expect": true
            },
            "rules": {
                "max-len": "off",
                "no-unused-expressions": "off"
            }
        }
    ],

    "rules": {
        "arrow-parens": [
            "error",
            "as-needed",
            { "requireForBlockBody": true }
        ],

        "import/extensions": ["error", "always"],

        "import/prefer-default-export": "off",

        "indent": ["error", 4],

        "no-restricted-syntax": [
            "error",
            {
                "selector": "ForInStatement",
                "message": "for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array."
            },
            {
                "selector": "LabeledStatement",
                "message": "Labels are a form of GOTO; using them makes code confusing and hard to maintain and understand."
            },
            {
                "selector": "WithStatement",
                "message": "`with` is disallowed in strict mode because it makes code impossible to predict and optimize."
            }
        ],

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

        "prefer-const": "off",

        "quotes": ["error", "double"]
    }
}