.eslintrc.json

{
    "root": true,
    "env": {
        "browser": true,
        "es6": true
    },
    "extends": "eslint:recommended",
    "parserOptions": {
        "ecmaVersion": 2015
    },
    "globals": {
        "Drupal": true,
        "drupalSettings": true,
        "drupalTranslations": true,
        "jQuery": true,
        "_": true,
        "Cookies": true,
        "Backbone": true,
        "Modernizr": true,
        "Popper": true,
        "Shepherd": true,
        "Sortable": true,
        "once": true,
        "CKEDITOR": true,
        "tabbable": true
    },
    "rules": {
        "indent": [
            "error",
            2
        ],
        "linebreak-style": [
            "error",
            "unix"
        ],
        "quotes": [
            "warn",
            "single"
        ],
        "semi": [
            "error",
            "always"
        ],
        "consistent-return": ["off"],
        "no-underscore-dangle": ["off"],
        "max-nested-callbacks": ["warn", 5],
        "no-plusplus": ["warn", {
            "allowForLoopAfterthoughts": true
        }],
        "no-param-reassign": ["off"],
        "no-prototype-builtins": ["off"],
        "valid-jsdoc": ["warn", {
            "prefer": {
                "returns": "return",
                "property": "prop"
            },
            "requireReturn": false
        }],
        "no-unused-vars": ["warn"],
        "operator-linebreak": ["error", "after", { "overrides": { "?": "ignore", ":": "ignore" } }]
    }
}