.eslintrc.json

{
  "env": {
    "es6": true,
    "node": true,
    "jest": true
  },
  "extends": "eslint:recommended",
  "rules": {
    "quotes": ["error", "single"],
    "semi": ["error", "always"],
    "indent": ["error", 2],
    "linebreak-style": ["error", "unix"],
    "no-console": "warn",           
    "no-unused-vars": "warn",       
    "no-alert": "error",            
    "prefer-const": "error",        
    "no-var": "error",
    "arrow-parens": ["error", "always"],
    "no-tabs": "error"
  },
  "parserOptions": {
    "ecmaVersion": 2017
  }
}