[Javascript] Linting JavaScript with ESLint

ESLint is a JavaScript linter (static analysis tool) that offers full support for ES6, JSX, and other modern tools via plugins. We walk through setting up ESLint in a project, using the "init" CLI tool, configuring warnings/errors for rules, and adding editor plugins and build integrations. ESLint is built to be "pluggable" with simple, extendable, modular rules and an API for writing and using plugins. ESLint has many rules which are all turned off by default; you can extend the core "recommended" rules which will catch common JavaScript errors, and you can also turn on stylistic rules for code consistency.

Install:

npm install eslint --save-dev
npm install -g eslint

Run:

eslint --init   or eslint index.js main.js

Will create an .eslintrc file for you.

{
    "rules": {
        "indent": [
            2,
            "tab"
        ],
        "quotes": [
            2,
            "single"
        ],
        "linebreak-style": [
            2,
            "windows"
        ],
        "semi": [
            2,
            "always"
        ]
    },
    "env": {
        "es6": true,
        "node": true,
        "browser": true
    },
    "extends": "eslint:recommended"
}

Check http://eslint.org/docs/rules/ for more docs.

In package.json:

  "scripts": {
    "lint": "eslint **.js"
  },

Add no-unused-var warning:

{
    "rules": {
        "indent": [
            2,
            "tab"
        ],
        "quotes": [
            2,
            "single"
        ],
        "linebreak-style": [
            2,
            "windows"
        ],
        "semi": [
            2,
            "always"
        ],
        "no-unused-vars": 1 // no var -> 1: warning, 2: error, 0: ignore
    },
    "env": {
        "es6": true,
        "node": true,
        "browser": true
    },
    "extends": "eslint:recommended"
}