.eslintrc.js

module.exports = {
  /** 
   * ESLint: http://eslint.org/docs/user-guide/configuring
   */

  // "env:" supplies predefined global variables
  'env': {
    'browser': true,
    'es6': true,
    'node': true,
    'mocha': true,
    'mongo': true,
    'jquery': true
  },
  'globals': {
    'supertest': true,
    'expect': true
  },
  // our configuration extends the recommended base configuration
  'extends': 'eslint:recommended',
  // define the type of file `script` or `module` for ES6 Modules
  'parserOptions': {
    'sourceType': 'module'
  },
  //ESLint rules: Severity Levels: off = 0 | warn = 1 | error = 2
  'rules': {
    'strict': ['error', 'safe'], //prefer `'use-strict';` pragma
    'eqeqeq': 'error', //prefer strict equality `===`
    'no-console': 'warn', //allows but warn about console like `console.log()`
    'no-unused-vars': 'warn', //warns about unused variables
    'no-eval': 'error', //disallows `eval()` usage
    'indent': ['error', 2], //enforce 2 space indents (not tabs)        
    'quotes': ['error', 'single'], //prefer single quotes over double quotes
    'semi': ['error', 'always'] //enforce semi-colon usage
  }
};