A CLI, or command line interface is a program desgined to start and complete one off tasks. Like git or npm. Node.js is a perfect runtime to create a CLI that will run on any machine that has Node.js isntalled.

Creating a CLI

Creating a CLI in Node.js just takes a extra step or two because they are really just an ordinary Node.js app wrapped behind a bin command. For this exercise, we'll create a CLI that opens a random reddit post in our browser. To start, we'll create a new folder and make it a package with npm init.

Once inside that folder, create a file reddit.mjs:

// reddit.mjs
#! /usr/bin/env node

console.log('hello from your CLI')

The fist line on that file is called a shabang or hashbang. It's needed to tell the machine where the interpreter is located that is needed to execute this file. For us, that will be Node.js.

Next we need to tell Node.js what the name of our CLI is so when can actually use it in our terminal. Just have to add a section to our package.json:

"bin": {
  "reddit": "./reddit.mjs"
}

Once installed, this package will have it's bin command installed into your machine's bin folder allowing us to use the reddit command.

Lastly, we must install our own package locally so we can test out the CLI. We could just execute the file with the node runtime, but we want to see the CLI actually work.

npm install -g

We can simply instll with no args which tells npm to install the current director. The -g flag means we want to globally install this package vs in a local node_modules.

You should now be able to run reddit and see your log print.

Packages in our Pacakge

Now to realize our dream of our reddit CLI opening a random reddit post, we have some work to do. Luckily for us, we can use NPM to install some packages to help.

npm install open node-fetch yargs --save

We'll install just these three packages.

open - will open our browser with a URL
node-fetch - is a fetch client that we can use to hit the reddit API
yargs - will allow us to process any flags or arguments passed to the CLI

So to put it all together

#! /usr/bin/env node
// import our packages
import open from 'open'
import fetch from 'node-fetch'
import yargs from 'yargs'

// parse env vars
const { argv } = yargs(process.argv)
// init fetch to reddit api
const res = await fetch('https://www.reddit.com/.json')
const data = await res.json()
const randomIndex = Math.floor(Math.random() * data.data.children.length)
// get radom post from reddit api response of all posts on front page
const post = data.data.children[randomIndex]

// log if --print flag is passed
if (argv.print) {
  console.log(`
    Title: ${post.data.title}\n
    Link: ${post.data.permalink}
  `)
} else {
  // open in browser if not
  open(`https://reddit.com${post.data.permalink}`)
}

With just a few lines of JS we were able to create a really powerful CLI with room for improvement. Like adding more options via flags. Even adding sub commands.

CLIs

Creating a CLI

Packages in our Pacakge