.eslintrc

{
  "parser": "babel-eslint",
  "env": {
    "browser": true,
    "node": true,
    "es6": true
  },
  "parserOptions": {
    "ecmaVersion": 2017,
    "sourceType": "module"
  },
  "globals": {
    "Polymer": true
  },
  "rules": {
    "no-undef": 2,
    "no-redeclare": 2,
    "no-unused-vars": 2,

    "no-cond-assign": 0,
    "no-console": 0,
    "no-extra-parens": 2,

    "block-scoped-var": 2,
    "eqeqeq": [2, "smart"],
    "no-else-return": 2,
    "no-floating-decimal": 2,
    "wrap-iife": [2, "inside"],
    "no-use-before-define": 1,

    "brace-style": 2,
    "camelcase": 2,
    "no-lonely-if": 2,
    "keyword-spacing": 2,
    "space-in-brackets": 0,
    "space-infix-ops": 2,

    "strict": [2, "never"],
    "indent": "off",
    "indent-legacy": [2, 2, {"VariableDeclarator": { "var": 2, "let": 2, "const": 3 }}],
    "quotes": [2, "single", { "allowTemplateLiterals": true }],
    "one-var": [2, {
      "let": "always"
    }]
  }
}