How to write command line tools in JavaScript with Node.js

Let's start by creating a project using npm

mkdir zaiste-cli cd zaiste-cli npm init

It will initialize a project directory with a package.json file. This file is used by npm to determine project dependencies and other configuration.

{
  "name": "zaiste-cli",
  "version": "0.0.1",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}

Let's adjust it by

• removing the main entry as it's only used with the module system
• adding preferGlobal set to true, npm will warn that the module is designed to be installed globally.
• adding the bin entry which maps commands to files

{
  "name": "zaiste-cli",
  "version": "0.0.1",
  "description": "",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "preferGlobal": true,
  "bin": {
    "zaiste-cli": "index.js"
  }
}

Now, let's create index.js. For the vanila JavaScript we define a shebang with node, for ES2015 we use babel-node.

#! /usr/bin/env babel-node

console.log('Hello ES2015');
console.log(process.argv);

var args = process.argv.slice(2);
console.log(args);

Finally let's run npm link to install the script on our system and execute it

zaiste-cli hello world

Once the script is done, you can publish it using npm publish so people could install it with npm install -g zaiste-cli.